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\n  \n 2024\n \n \n (6)\n \n \n
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\n \n\n \n \n \n \n \n Two-dimensional photonic crystal cavities in ZnSe quantum well structures.\n \n \n \n\n\n \n Qiao, S., den Driesch, N. v., Chen, X., Trellenkamp, S., Lentz, F., Krause, C., Bennemann, B., Brazda, T., LeBeau, J. M, & Pawlis, A.\n\n\n \n\n\n\n . February 2024.\n \n\n\n\n
\n\n\n\n \n\n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Qiao2024-ta,\n  title         = "Two-dimensional photonic crystal cavities in {ZnSe} quantum\n                   well structures",\n  author        = "Qiao, Siqi and den Driesch, Nils von and Chen, Xi and\n                   Trellenkamp, Stefan and Lentz, Florian and Krause, Christoph\n                   and Bennemann, Benjamin and Brazda, Thorsten and LeBeau,\n                   James M and Pawlis, Alexander",\n  abstract      = "ZnSe and related materials like ZnMgSe and ZnCdSe are\n                   promising II-VI host materials for optically mediated\n                   quantum information technology such as single photon sources\n                   or spin qubits. Integrating these heterostructures into\n                   photonic crystal (PC) cavities enables further improvements,\n                   for example realizing Purcell-enhanced single photon sources\n                   with increased quantum efficiency. Here we report on the\n                   successful implementation of two-dimensional (2D) PC\n                   cavities in strained ZnSe quantum wells (QW) on top of a\n                   novel AlAs supporting layer. This approach overcomes typical\n                   obstacles associated with PC membrane fabrication in\n                   strained materials, such as cracks and strain relaxation in\n                   the corresponding devices. We demonstrate the attainment of\n                   the required mechanical stability in our PC devices,\n                   complete strain retainment and effective vertical optical\n                   confinement. Structural analysis of our PC cavities reveals\n                   excellent etching anisotropy. Additionally, elemental\n                   mapping in a scanning transmission electron microscope\n                   confirms the transformation of AlAs into AlOx by post-growth\n                   wet oxidation and reveals partial oxidation of ZnMgSe at the\n                   etched sidewalls in the PC. This knowledge is utilized to\n                   tailor FDTD simulations and to extract the ZnMgSe dispersion\n                   relation with small oxygen content. Optical characterization\n                   of the PC cavities with cross-polarized resonance scattering\n                   spectroscopy verifies the presence of cavity modes. The\n                   excellent agreement between simulation and measured cavity\n                   mode energies demonstrates wide tunability of the PC cavity\n                   and proves the pertinence of our model. This implementation\n                   of 2D PC cavities in the ZnSe material system establishes a\n                   solid foundation for future developments of ZnSe quantum\n                   devices.",\n  month         =  feb,\n  year          =  2024,\n  keywords      = "PECASE 2023-2024;LeBeau Group",\n  archivePrefix = "arXiv",\n  eprint        = "2402.15349",\n  primaryClass  = "cond-mat.mtrl-sci",\n  arxivid       = "2402.15349"\n}\n\n
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\n ZnSe and related materials like ZnMgSe and ZnCdSe are promising II-VI host materials for optically mediated quantum information technology such as single photon sources or spin qubits. Integrating these heterostructures into photonic crystal (PC) cavities enables further improvements, for example realizing Purcell-enhanced single photon sources with increased quantum efficiency. Here we report on the successful implementation of two-dimensional (2D) PC cavities in strained ZnSe quantum wells (QW) on top of a novel AlAs supporting layer. This approach overcomes typical obstacles associated with PC membrane fabrication in strained materials, such as cracks and strain relaxation in the corresponding devices. We demonstrate the attainment of the required mechanical stability in our PC devices, complete strain retainment and effective vertical optical confinement. Structural analysis of our PC cavities reveals excellent etching anisotropy. Additionally, elemental mapping in a scanning transmission electron microscope confirms the transformation of AlAs into AlOx by post-growth wet oxidation and reveals partial oxidation of ZnMgSe at the etched sidewalls in the PC. This knowledge is utilized to tailor FDTD simulations and to extract the ZnMgSe dispersion relation with small oxygen content. Optical characterization of the PC cavities with cross-polarized resonance scattering spectroscopy verifies the presence of cavity modes. The excellent agreement between simulation and measured cavity mode energies demonstrates wide tunability of the PC cavity and proves the pertinence of our model. This implementation of 2D PC cavities in the ZnSe material system establishes a solid foundation for future developments of ZnSe quantum devices.\n
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\n \n\n \n \n \n \n \n Antiferroelectric Nanodomains Stabilized by Chemical Disorder at Anti-phase Boundaries.\n \n \n \n\n\n \n Zhu, M., Xu, M., Yun, Y., Wu, L., Shafir, O., Gilgenbach, C., Martin, L. W, Grinberg, I., Spanier, J. E, & LeBeau, J. M\n\n\n \n\n\n\n . March 2024.\n \n\n\n\n
\n\n\n\n \n\n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Zhu2024-rv,\n  title         = "Antiferroelectric Nanodomains Stabilized by Chemical\n                   Disorder at Anti-phase Boundaries",\n  author        = "Zhu, Menglin and Xu, Michael and Yun, Yu and Wu, Liyan and\n                   Shafir, Or and Gilgenbach, Colin and Martin, Lane W and\n                   Grinberg, Ilya and Spanier, Jonathan E and LeBeau, James M",\n  abstract      = "Antiferroelectric perovskite oxides exhibit exceptional\n                   dielectric properties and high structural/chemical\n                   tunability, making them promising for a wide range of\n                   applications from high energy-density capacitors to\n                   solid-state cooling. However, tailoring the\n                   antiferroelectric phase stability through alloying is\n                   hampered by the complex interplay between chemistry and the\n                   alignment of dipole moments. In this study, correlations\n                   between chemical order and the stability of the\n                   antiferroelectric phase are established at anti-phase\n                   boundaries in \\textbackslashce\\{Pb2MgWO6\\}. Using multislice\n                   ptychography, we reveal the three-dimensional nature of\n                   chemical order at the boundaries and show that they exhibit\n                   a finite width of chemical intermixing. Furthermore, regions\n                   at and adjacent to the anti-phase boundary exhibit\n                   antiferroelectric displacements in contrast to the overall\n                   paraelectric film. Combining spatial statistics and density\n                   functional theory simulations, local antiferroelectric\n                   distortions are shown to be confined to and stabilized by\n                   chemical disorder. Enabled by the three-dimensional\n                   information of multislice ptychography, these results\n                   provide insights into the interplay between chemical order\n                   and electronic properties to engineer antiferroelectric\n                   material response.",\n  month         =  mar,\n  year          =  2024,\n  keywords      = "LeBeau Group",\n  archivePrefix = "arXiv",\n  eprint        = "2403.04904",\n  primaryClass  = "cond-mat.mtrl-sci",\n  arxivid       = "2403.04904"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Antiferroelectric perovskite oxides exhibit exceptional dielectric properties and high structural/chemical tunability, making them promising for a wide range of applications from high energy-density capacitors to solid-state cooling. However, tailoring the antiferroelectric phase stability through alloying is hampered by the complex interplay between chemistry and the alignment of dipole moments. In this study, correlations between chemical order and the stability of the antiferroelectric phase are established at anti-phase boundaries in ȩ\\Pb2MgWO6\\. Using multislice ptychography, we reveal the three-dimensional nature of chemical order at the boundaries and show that they exhibit a finite width of chemical intermixing. Furthermore, regions at and adjacent to the anti-phase boundary exhibit antiferroelectric displacements in contrast to the overall paraelectric film. Combining spatial statistics and density functional theory simulations, local antiferroelectric distortions are shown to be confined to and stabilized by chemical disorder. Enabled by the three-dimensional information of multislice ptychography, these results provide insights into the interplay between chemical order and electronic properties to engineer antiferroelectric material response.\n
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\n \n\n \n \n \n \n \n Perovskite‐derived layered crystal structure in SrCo$_{0.26}$Fe$_{0.74}$O$_{3‐δ}$ thin films.\n \n \n \n\n\n \n Cho, E., Kumar, A., Ning, S., LeBeau, J. M, & Ross, C. A\n\n\n \n\n\n\n Adv. Mater. Interfaces. January 2024.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
\n
@ARTICLE{Cho2024-pm,\n  title     = "Perovskite‐derived layered crystal structure in\n               {SrCo$_{0.26}$Fe$_{0.74}$O$_{3‐\\delta}$} thin films",\n  author    = "Cho, Eunsoo and Kumar, Abinash and Ning, Shuai and LeBeau, James\n               M and Ross, Caroline A",\n  abstract  = "AbstractOxygen coordination and vacancy ordering play an\n               important role in dictating the functionality of complex oxides.\n               In this work, an unconventional layering of oxygen ions in a\n               mixed conductor SrCo1‐xFexO3‐$\\delta$ (SCFO) thin film grown\n               epitaxially on SrTiO3 (STO) is reported. Scanning transmission\n               electron microscopy (STEM) reveals alternating layers of oxygen\n               deficiency along the growth direction, with the oxygen‐rich\n               layer correlated with the neighboring Co,Fe‐site intensity, and\n               contraction of the Sr--Sr distance. Density functional theory\n               (DFT) calculations and STEM image simulations support the\n               emergence of periodic (Co,Fe)O6 and (Co,Fe)O4/(Co,Fe)O5 layers,\n               an ordering that is also sensitive to the Co:Fe ratio.",\n  journal   = "Adv. Mater. Interfaces",\n  publisher = "Wiley",\n  month     =  jan,\n  year      =  2024,\n  keywords  = "LeBeau Group",\n  copyright = "http://creativecommons.org/licenses/by/4.0/",\n  language  = "en",\n  issn      = "2196-7350",\n  doi       = "10.1002/admi.202300807"\n}\n\n
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\n AbstractOxygen coordination and vacancy ordering play an important role in dictating the functionality of complex oxides. In this work, an unconventional layering of oxygen ions in a mixed conductor SrCo1‐xFexO3‐$δ$ (SCFO) thin film grown epitaxially on SrTiO3 (STO) is reported. Scanning transmission electron microscopy (STEM) reveals alternating layers of oxygen deficiency along the growth direction, with the oxygen‐rich layer correlated with the neighboring Co,Fe‐site intensity, and contraction of the Sr–Sr distance. Density functional theory (DFT) calculations and STEM image simulations support the emergence of periodic (Co,Fe)O6 and (Co,Fe)O4/(Co,Fe)O5 layers, an ordering that is also sensitive to the Co:Fe ratio.\n
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\n \n\n \n \n \n \n \n Composition-dependent transformation-induced plasticity in Co-based complex concentrated alloys.\n \n \n \n\n\n \n Oh, H. S., Xu, M., Wei, S., Worsnop, F. F, LeBeau, J. M, & Tasan, C C.\n\n\n \n\n\n\n Acta Mater., 262: 119349. January 2024.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
\n
@ARTICLE{Oh2024-tc,\n  title    = "Composition-dependent transformation-induced plasticity in\n              Co-based complex concentrated alloys",\n  author   = "Oh, Hyun Seok and Xu, Michael and Wei, Shaolou and Worsnop,\n              Felicity F and LeBeau, James M and Tasan, C Cem",\n  abstract = "While the mechanically-induced martensitic transformation and\n              transformation-induced plasticity (TRIP) effects have various\n              known benefits, transformation of blocky martensite can also\n              accelerate ductile damage nucleation and growth. Some\n              complex-concentrated alloys (CCAs) with negative stacking-fault\n              energy (SFE) demonstrate a rare faulting plasticity behavior with\n              high strain hardening capability, that sets them apart from\n              conventional low, positive SFE alloys that exhibit the TRIP\n              effect. This study investigates the influence of dilute nitrogen\n              on the TRIP mechanisms in a Co-rich CoCrNi CCA, and reveals,\n              among other findings, that nitrogen interstitials can effectively\n              reduce the extension of stacking faults and deformation-induced\n              phase transformation, resulting in higher strain hardenability at\n              early deformation levels and ductility. Thermodynamic\n              calculations are coupled to various experimental analyses based\n              on atom-probe tomography, scanning transmission electron\n              microscopy, electron backscattered diffraction,\n              electron-channeling contrast imaging, in situ high-energy\n              synchrotron X-ray diffraction, and stress relaxation testing, to\n              explore the origins of the observation. This work provides\n              insights into the future design of CCAs with desirable TRIP,\n              faulting plasticity, and mechanical properties.",\n  journal  = "Acta Mater.",\n  volume   =  262,\n  pages    = "119349",\n  month    =  jan,\n  year     =  2024,\n  keywords = "Complex concentrated alloy; Negative stacking fault energy;\n              Nitrogen; Faulting-induced plasticity; Transformation-induced\n              plasticity;LeBeau Group",\n  issn     = "1359-6454",\n  doi      = "10.1016/j.actamat.2023.119349"\n}\n\n
\n
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\n While the mechanically-induced martensitic transformation and transformation-induced plasticity (TRIP) effects have various known benefits, transformation of blocky martensite can also accelerate ductile damage nucleation and growth. Some complex-concentrated alloys (CCAs) with negative stacking-fault energy (SFE) demonstrate a rare faulting plasticity behavior with high strain hardening capability, that sets them apart from conventional low, positive SFE alloys that exhibit the TRIP effect. This study investigates the influence of dilute nitrogen on the TRIP mechanisms in a Co-rich CoCrNi CCA, and reveals, among other findings, that nitrogen interstitials can effectively reduce the extension of stacking faults and deformation-induced phase transformation, resulting in higher strain hardenability at early deformation levels and ductility. Thermodynamic calculations are coupled to various experimental analyses based on atom-probe tomography, scanning transmission electron microscopy, electron backscattered diffraction, electron-channeling contrast imaging, in situ high-energy synchrotron X-ray diffraction, and stress relaxation testing, to explore the origins of the observation. This work provides insights into the future design of CCAs with desirable TRIP, faulting plasticity, and mechanical properties.\n
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\n \n\n \n \n \n \n \n Frictional ignition of dispersion-strengthened Ni-Cr alloys.\n \n \n \n\n\n \n Jimenez, A. G., Wabel, T., Bendana, F. A, DeSain, J. D, Xu, M., LeBeau, J. M, & Cordero, Z. C\n\n\n \n\n\n\n Tribol. Int.,109370. February 2024.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
\n
@ARTICLE{Jimenez2024-kn,\n  title    = "Frictional ignition of dispersion-strengthened {Ni-Cr} alloys",\n  author   = "Jimenez, Andres Garcia and Wabel, Timothy and Bendana, Fabio A\n              and DeSain, John D and Xu, Michael and LeBeau, James M and\n              Cordero, Zachary C",\n  abstract = "Frictional heating of metals at reciprocating or sliding contacts\n              in high-pressure oxygen environments can result in catastrophic\n              metal fires. This process of frictional ignition has been linked\n              to several high-profile failures in oxidizer-rich turbopumps, and\n              it remains an ongoing challenge in the development of\n              next-generation reusable rocket engines. In early NASA studies on\n              frictional ignition of candidate turbine materials, oxide\n              dispersion-strengthened Ni-base superalloys were found to be\n              exceptionally ignition-resistant. Here we have assessed the\n              tribological phenomena that impart this behavior through\n              high-speed sliding, frictional ignition experiments on binary\n              Ni-Cr alloys and the oxide dispersion-strengthened Ni-Cr alloys\n              MA754 and MA758. The rubbing surfaces on recovered non-ignited\n              samples were coated with oxide tribolayers that formed in situ\n              during sliding. An order of magnitude decrease in friction\n              coefficient during the early stages of sliding resulted from\n              tribolayer growth. An abrupt increase in friction coefficient\n              before ignition was linked to tribolayer breakdown, which exposed\n              the hot underlying metal to high-pressure oxygen. The oxide\n              dispersion-strengthened alloy MA754 was the only material that\n              did not ignite under any test conditions. Its specific content of\n              Cr and Y2O3 dispersoids synergistically promote rapid growth of a\n              thick, adherent oxide tribolayer strengthened by refractory\n              Ni2CrO4 precipitates. These features collectively mitigate\n              tribolayer breakdown, suppressing ignition. The present results\n              highlight the importance of tribolayer stability in frictional\n              ignition resistance and suggest alloy design strategies for\n              tailoring oxidational wear behaviors to achieve intrinsically\n              ignition-resistant materials.",\n  journal  = "Tribol. Int.",\n  pages    = "109370",\n  month    =  feb,\n  year     =  2024,\n  keywords = "tribochemistry; alloy design; oxidation; sliding wear; metal\n              combustion;LeBeau Group",\n  issn     = "0301-679X",\n  doi      = "10.1016/j.triboint.2024.109370"\n}\n\n
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\n Frictional heating of metals at reciprocating or sliding contacts in high-pressure oxygen environments can result in catastrophic metal fires. This process of frictional ignition has been linked to several high-profile failures in oxidizer-rich turbopumps, and it remains an ongoing challenge in the development of next-generation reusable rocket engines. In early NASA studies on frictional ignition of candidate turbine materials, oxide dispersion-strengthened Ni-base superalloys were found to be exceptionally ignition-resistant. Here we have assessed the tribological phenomena that impart this behavior through high-speed sliding, frictional ignition experiments on binary Ni-Cr alloys and the oxide dispersion-strengthened Ni-Cr alloys MA754 and MA758. The rubbing surfaces on recovered non-ignited samples were coated with oxide tribolayers that formed in situ during sliding. An order of magnitude decrease in friction coefficient during the early stages of sliding resulted from tribolayer growth. An abrupt increase in friction coefficient before ignition was linked to tribolayer breakdown, which exposed the hot underlying metal to high-pressure oxygen. The oxide dispersion-strengthened alloy MA754 was the only material that did not ignite under any test conditions. Its specific content of Cr and Y2O3 dispersoids synergistically promote rapid growth of a thick, adherent oxide tribolayer strengthened by refractory Ni2CrO4 precipitates. These features collectively mitigate tribolayer breakdown, suppressing ignition. The present results highlight the importance of tribolayer stability in frictional ignition resistance and suggest alloy design strategies for tailoring oxidational wear behaviors to achieve intrinsically ignition-resistant materials.\n
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\n \n\n \n \n \n \n \n Modeling Temperature-Dependent Electron Thermal Diffuse Scattering via Machine-Learned Interatomic Potentials and Path-Integral Molecular Dynamics.\n \n \n \n\n\n \n Kim, D. S, Xu, M., & LeBeau, J. M\n\n\n \n\n\n\n Phys. Rev. Lett., 132(8): 086301. February 2024.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Kim2024-qi,\n  title     = "Modeling {Temperature-Dependent} Electron Thermal Diffuse\n               Scattering via {Machine-Learned} Interatomic Potentials and\n               {Path-Integral} Molecular Dynamics",\n  author    = "Kim, Dennis S and Xu, Michael and LeBeau, James M",\n  journal   = "Phys. Rev. Lett.",\n  publisher = "American Physical Society",\n  volume    =  132,\n  number    =  8,\n  pages     = "086301",\n  month     =  feb,\n  year      =  2024,\n  keywords  = "LeBeau Group;PECASE 2023-2024",\n  issn      = "0031-9007",\n  doi       = "10.1103/PhysRevLett.132.086301"\n}\n\n
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\n  \n 2023\n \n \n (15)\n \n \n
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\n \n\n \n \n \n \n \n Validation of machine-learned interatomic potentials via temperature-dependent electron thermal diffuse scattering.\n \n \n \n\n\n \n Kim, D. S, Xu, M., & LeBeau, J. M\n\n\n \n\n\n\n . March 2023.\n \n\n\n\n
\n\n\n\n \n\n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Kim2023-dd,\n  title         = "Validation of machine-learned interatomic potentials via\n                   temperature-dependent electron thermal diffuse scattering",\n  author        = "Kim, Dennis S and Xu, Michael and LeBeau, James M",\n  abstract      = "Machine-learned interatomic potentials (MLIPs) show promise\n                   in accurately describing the physical properties of\n                   materials, but there is a need for a higher throughput\n                   method of validation. Here, we demonstrate using that MLIPs\n                   and molecular dynamics can accurately capture the potential\n                   energy landscape and lattice dynamics that are needed to\n                   describe electron thermal diffuse scattering. Using\n                   SrTiO$_3$ as a test-bed at cryogenic and room temperatures,\n                   we compare electron thermal diffuse scattering simulations\n                   using different approximations to incorporate thermal\n                   motion. Only when the simulations are based on quantum\n                   mechanically accurate MLIPs in combination with\n                   path-integral molecular dynamics that include nuclear\n                   quantum effects, there is excellent agreement with\n                   experiment\\textbackslashend\\{abstract\\}",\n  month         =  mar,\n  year          =  2023,\n  keywords      = "LeBeau Group;PECASE;AFOSR",\n  archivePrefix = "arXiv",\n  eprint        = "2303.02519",\n  primaryClass  = "cond-mat.mtrl-sci",\n  arxivid       = "2303.02519"\n}\n\n
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\n Machine-learned interatomic potentials (MLIPs) show promise in accurately describing the physical properties of materials, but there is a need for a higher throughput method of validation. Here, we demonstrate using that MLIPs and molecular dynamics can accurately capture the potential energy landscape and lattice dynamics that are needed to describe electron thermal diffuse scattering. Using SrTiO$_3$ as a test-bed at cryogenic and room temperatures, we compare electron thermal diffuse scattering simulations using different approximations to incorporate thermal motion. Only when the simulations are based on quantum mechanically accurate MLIPs in combination with path-integral molecular dynamics that include nuclear quantum effects, there is excellent agreement with experiment\\end\\abstract\\\n
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\n \n\n \n \n \n \n \n Sampling metrics for robust reconstructions in multislice ptychography: Theory and experiment.\n \n \n \n\n\n \n Gilgenbach, C., Chen, X., & LeBeau, J. M\n\n\n \n\n\n\n . November 2023.\n \n\n\n\n
\n\n\n\n \n\n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
\n
@ARTICLE{Gilgenbach2023-mj,\n  title         = "Sampling metrics for robust reconstructions in multislice\n                   ptychography: Theory and experiment",\n  author        = "Gilgenbach, Colin and Chen, Xi and LeBeau, James M",\n  abstract      = "While multislice electron ptychography can provide\n                   thermal-vibration limited resolution and 3D information, it\n                   relies on the proper selection of many intertwined\n                   experimental and computational parameters. Here, we outline\n                   a theoretical basis for selecting experimental parameters to\n                   enable robust ptychographic reconstructions. We develop a\n                   series of physically informed metrics to describe the\n                   selection of experimental parameters in multislice\n                   ptychography. Image simulations are used to comprehensively\n                   evaluate the validity of these metrics over a broad range of\n                   experimental conditions. We develop two metrics, areal\n                   oversampling and Ronchigram magnification, which predict\n                   reconstruction success with high accuracy. Lastly, we\n                   validate these conclusions with experimental ptychographic\n                   data, and demonstrate close agreement between trends in\n                   simulated and experimental data. Using these metrics, we\n                   achieve experimental multislice reconstructions at a scan\n                   step of $1.0 \\unit\\{\\AA/px\\}$, enabling large field-of-view\n                   ($>\\!18\\unit\\{nm\\}$), data-efficient reconstructions. These\n                   experimental design principles enable the routine and\n                   reliable use of multislice ptychography for materials\n                   characterization.",\n  month         =  nov,\n  year          =  2023,\n  keywords      = "LeBeau Group;PECASE 2023-2024",\n  archivePrefix = "arXiv",\n  eprint        = "2311.15181",\n  primaryClass  = "cond-mat.mtrl-sci",\n  arxivid       = "2311.15181"\n}\n\n
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\n While multislice electron ptychography can provide thermal-vibration limited resolution and 3D information, it relies on the proper selection of many intertwined experimental and computational parameters. Here, we outline a theoretical basis for selecting experimental parameters to enable robust ptychographic reconstructions. We develop a series of physically informed metrics to describe the selection of experimental parameters in multislice ptychography. Image simulations are used to comprehensively evaluate the validity of these metrics over a broad range of experimental conditions. We develop two metrics, areal oversampling and Ronchigram magnification, which predict reconstruction success with high accuracy. Lastly, we validate these conclusions with experimental ptychographic data, and demonstrate close agreement between trends in simulated and experimental data. Using these metrics, we achieve experimental multislice reconstructions at a scan step of $1.0 ˘nit\\{Å/px\\}$, enabling large field-of-view ($>\\!18˘nit\\{nm\\}$), data-efficient reconstructions. These experimental design principles enable the routine and reliable use of multislice ptychography for materials characterization.\n
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\n \n\n \n \n \n \n \n Expanding the perovskite periodic table to include chalcogenide alloys with tunable band gap spanning 1.5–1.9 eV.\n \n \n \n\n\n \n Sadeghi, I., Van Sambeek, J., Simonian, T., Xu, M., Ye, K., Cai, T., Nicolosi, V., LeBeau, J. M, & Jaramillo, R.\n\n\n \n\n\n\n Adv. Funct. Mater.. August 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Sadeghi2023-py,\n  title     = "Expanding the perovskite periodic table to include chalcogenide\n               alloys with tunable band gap spanning 1.5--1.9 eV",\n  author    = "Sadeghi, Ida and Van Sambeek, Jack and Simonian, Tigran and Xu,\n               Michael and Ye, Kevin and Cai, Tao and Nicolosi, Valeria and\n               LeBeau, James M and Jaramillo, Rafael",\n  abstract  = "AbstractOptoelectronic technologies are based on families of\n               semiconductor alloys. It is rare that a new semiconductor alloy\n               family is developed to the point where epitaxial growth is\n               possible; since the 1950s, this has happened approximately once\n               per decade. Herein, this work demonstrates epitaxial thin film\n               growth of semiconducting chalcogenide perovskite alloys in the\n               Ba‐Zr‐S‐Se system by gas‐source molecular beam epitaxy (MBE).\n               This work stabilizes the full range y = 0 − 3 of compositions\n               BaZrS(3‐y)Sey in the perovskite structure. The resulting films\n               are environmentally stable and the direct band gap (Eg) varies\n               strongly with Se content, as predicted by theory, with Eg = 1.9\n               − 1.5 eV for y = 0 − 3. This creates possibilities for visible\n               and near‐infrared (VIS--NIR) optoelectronics, solid‐state\n               lighting, and solar cells using chalcogenide perovskites.",\n  journal   = "Adv. Funct. Mater.",\n  publisher = "Wiley",\n  month     =  aug,\n  year      =  2023,\n  keywords  = "LeBeau Group;PECASE 2023-2024",\n  copyright = "http://creativecommons.org/licenses/by/4.0/",\n  language  = "en",\n  issn      = "1616-301X, 1616-3028",\n  doi       = "10.1002/adfm.202304575"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n AbstractOptoelectronic technologies are based on families of semiconductor alloys. It is rare that a new semiconductor alloy family is developed to the point where epitaxial growth is possible; since the 1950s, this has happened approximately once per decade. Herein, this work demonstrates epitaxial thin film growth of semiconducting chalcogenide perovskite alloys in the Ba‐Zr‐S‐Se system by gas‐source molecular beam epitaxy (MBE). This work stabilizes the full range y = 0 − 3 of compositions BaZrS(3‐y)Sey in the perovskite structure. The resulting films are environmentally stable and the direct band gap (Eg) varies strongly with Se content, as predicted by theory, with Eg = 1.9 − 1.5 eV for y = 0 − 3. This creates possibilities for visible and near‐infrared (VIS–NIR) optoelectronics, solid‐state lighting, and solar cells using chalcogenide perovskites.\n
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\n \n\n \n \n \n \n \n Revealing Site Occupancy in a Complex Oxide: Terbium Iron Garnet.\n \n \n \n\n\n \n Rosenberg, E., Bauer, J., Cho, E., Kumar, A., Pelliciari, J., Occhialini, C. A, Ning, S., Kaczmarek, A., Rosenberg, R., Freeland, J. W, Chen, Y., Wang, J., LeBeau, J., Comin, R., de Groot, F M F, & Ross, C. A\n\n\n \n\n\n\n Small,e2300824. April 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Rosenberg2023-iz,\n  title    = "Revealing Site Occupancy in a Complex Oxide: Terbium Iron Garnet",\n  author   = "Rosenberg, Ethan and Bauer, Jackson and Cho, Eunsoo and Kumar,\n              Abinash and Pelliciari, Jonathan and Occhialini, Connor A and\n              Ning, Shuai and Kaczmarek, Allison and Rosenberg, Richard and\n              Freeland, John W and Chen, Yu-Chia and Wang, Jian-Ping and\n              LeBeau, James and Comin, Riccardo and de Groot, F M F and Ross,\n              Caroline A",\n  abstract = "Complex oxide films stabilized by epitaxial growth can exhibit\n              large populations of point defects which have important effects\n              on their properties. The site occupancy of pulsed laser-deposited\n              epitaxial terbium iron garnet (TbIG) films with excess terbium\n              (Tb) is analyzed, in which the terbium:iron (Tb:Fe)ratio is 0.86\n              compared to the stoichiometric value of 0.6. The magnetic\n              properties of the TbIG are sensitive to site occupancy,\n              exhibiting a higher compensation temperature (by 90 K) and a\n              lower Curie temperature (by 40 K) than the bulk Tb3 Fe5 O12\n              garnet. Data derived from X-ray core-level spectroscopy,\n              magnetometry, and molecular field coefficient modeling are\n              consistent with occupancy of the dodecahedral sites by Tb3+ , the\n              octahedral sites by Fe3+ , Tb3+ and vacancies, and the\n              tetrahedral sites by Fe3+ and vacancies. Energy dispersive X-ray\n              spectroscopy in a scanning transmission electron microscope\n              provides direct evidence of TbFe antisites. A small fraction of\n              Fe2+ is present, and oxygen vacancies are inferred to be present\n              to maintain charge neutrality. Variation of the site occupancies\n              provides a path to considerable manipulation of the magnetic\n              properties of epitaxial iron garnet films and other complex\n              oxides, which readily accommodate stoichiometries not found in\n              their bulk counterparts.",\n  journal  = "Small",\n  pages    = "e2300824",\n  month    =  apr,\n  year     =  2023,\n  keywords = "complex oxides; defect engineering; epitaxial stabilization;\n              garnets; magnetic thin films;LeBeau Group",\n  language = "en",\n  issn     = "1613-6810, 1613-6829",\n  pmid     = "37060220",\n  doi      = "10.1002/smll.202300824"\n}\n\n
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\n Complex oxide films stabilized by epitaxial growth can exhibit large populations of point defects which have important effects on their properties. The site occupancy of pulsed laser-deposited epitaxial terbium iron garnet (TbIG) films with excess terbium (Tb) is analyzed, in which the terbium:iron (Tb:Fe)ratio is 0.86 compared to the stoichiometric value of 0.6. The magnetic properties of the TbIG are sensitive to site occupancy, exhibiting a higher compensation temperature (by 90 K) and a lower Curie temperature (by 40 K) than the bulk Tb3 Fe5 O12 garnet. Data derived from X-ray core-level spectroscopy, magnetometry, and molecular field coefficient modeling are consistent with occupancy of the dodecahedral sites by Tb3+ , the octahedral sites by Fe3+ , Tb3+ and vacancies, and the tetrahedral sites by Fe3+ and vacancies. Energy dispersive X-ray spectroscopy in a scanning transmission electron microscope provides direct evidence of TbFe antisites. A small fraction of Fe2+ is present, and oxygen vacancies are inferred to be present to maintain charge neutrality. Variation of the site occupancies provides a path to considerable manipulation of the magnetic properties of epitaxial iron garnet films and other complex oxides, which readily accommodate stoichiometries not found in their bulk counterparts.\n
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\n \n\n \n \n \n \n \n On the plastic deformation of a CoCrFeNiW-C alloy at elevated temperatures: Part I. Serrated plastic flow and its latent dynamics.\n \n \n \n\n\n \n Wei, S., Moriarty, D. P, Xu, M., LeBeau, J. M, & Tasan, C. C.\n\n\n \n\n\n\n Acta Mater., 242: 118430. January 2023.\n \n\n\n\n
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@ARTICLE{Wei2023-lz,\n  title    = "On the plastic deformation of a {CoCrFeNiW-C} alloy at elevated\n              temperatures: Part I. Serrated plastic flow and its latent\n              dynamics",\n  author   = "Wei, Shaolou and Moriarty, Daniel P and Xu, Michael and LeBeau,\n              James M and Tasan, Cemal Cem",\n  abstract = "Multi-component Co-alloys are a class of promising metallic\n              materials for high-temperature applications. The present work\n              primarily focuses on the plastic deformation mechanisms of a\n              CoCrFeNiW-C alloy at 650 °C, with emphases on dislocation slip\n              intermittency and plastic flow features. To this end, by\n              integrating in situ scanning electron microscopy-based tests,\n              statistical analyses, and theoretical calculations, several\n              mechanistic insights are revealed. In this material, the plastic\n              flow is featured by evident serration events with a\n              self-organized critical dynamic feature, where mixed Type A and B\n              serrations operate at a moderate deformation level, followed by\n              the onset of a higher magnitude Type B serration. As temperature\n              increases up to 700 and 750 °C, although more evident Type C\n              serration occurs, the self-organized criticality along with the\n              spatial-temporal power-law scaling relation remains nearly\n              unaffected. Microstructural relevance of the serration mechanisms\n              and the deformation substructural characteristics are also\n              explored in greater depth.",\n  journal  = "Acta Mater.",\n  volume   =  242,\n  pages    = "118430",\n  month    =  jan,\n  year     =  2023,\n  keywords = "Chaotic dynamics; Slip intermittency; Thermal activation;\n              Superalloys;LeBeau Group;DMREF",\n  issn     = "1359-6454",\n  doi      = "10.1016/j.actamat.2022.118430"\n}\n\n
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\n Multi-component Co-alloys are a class of promising metallic materials for high-temperature applications. The present work primarily focuses on the plastic deformation mechanisms of a CoCrFeNiW-C alloy at 650 °C, with emphases on dislocation slip intermittency and plastic flow features. To this end, by integrating in situ scanning electron microscopy-based tests, statistical analyses, and theoretical calculations, several mechanistic insights are revealed. In this material, the plastic flow is featured by evident serration events with a self-organized critical dynamic feature, where mixed Type A and B serrations operate at a moderate deformation level, followed by the onset of a higher magnitude Type B serration. As temperature increases up to 700 and 750 °C, although more evident Type C serration occurs, the self-organized criticality along with the spatial-temporal power-law scaling relation remains nearly unaffected. Microstructural relevance of the serration mechanisms and the deformation substructural characteristics are also explored in greater depth.\n
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\n \n\n \n \n \n \n \n Heterogeneous microstructural evolution during hydrodynamic penetration of a high-velocity copper microparticle impacting copper.\n \n \n \n\n\n \n Tiamiyu, A. A, Lucas, T., Pang, E. L, Chen, X., LeBeau, J. M, & Schuh, C. A\n\n\n \n\n\n\n Mater. Today. December 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Tiamiyu2023-fp,\n  title    = "Heterogeneous microstructural evolution during hydrodynamic\n              penetration of a high-velocity copper microparticle impacting\n              copper",\n  author   = "Tiamiyu, Ahmed A and Lucas, Tyler and Pang, Edward L and Chen, Xi\n              and LeBeau, James M and Schuh, Christopher A",\n  abstract = "Microparticle hydrodynamic penetration (HDP) may be associated\n              with the erosion regime in cold spray processing and other\n              high-velocity impact events. Here, in an experimental approach\n              where we can individually launch particles and study the impact\n              sites, we explore copper microparticles impacted on copper\n              substrates at velocities above 900 m/s where HDP begins. We lift\n              cross-sectional lamellae from the impact sites with a focused-ion\n              beam for further microstructural characterization using electron\n              backscatter diffraction and scanning transmission electron\n              microscopy. Due to the gradients of strain, strain rate, and\n              temperature associated with HDP, heterogeneous microstructures\n              result. The structural evolution processes observed include\n              deformation twinning and multiple dislocation-mediated grain\n              recrystallization mechanisms---geometric dynamic\n              recrystallization (gDRX), discontinuous DRX (dDRX), and meta DRX\n              (mDRX). The higher strains at the interface lead to the most\n              significant structural changes and complex mechanisms. In\n              contrast, there is a gradient to more conventional dislocation\n              plasticity away from the interface (on either the particle or\n              substrate side). These microstructural observations are\n              consistent with the deformation map for copper and extend the\n              observations of impact-induced recrystallization across new\n              regimes of behavior.",\n  journal  = "Mater. Today",\n  month    =  dec,\n  year     =  2023,\n  keywords = "High-velocity impact; Hydrodynamic particle penetration; Dynamic\n              recrystallization; Metadynamic recrystallization; Cold spray\n              process;LeBeau Group;PECASE 2023-2024",\n  issn     = "1369-7021",\n  doi      = "10.1016/j.mattod.2023.11.015"\n}\n\n
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\n Microparticle hydrodynamic penetration (HDP) may be associated with the erosion regime in cold spray processing and other high-velocity impact events. Here, in an experimental approach where we can individually launch particles and study the impact sites, we explore copper microparticles impacted on copper substrates at velocities above 900 m/s where HDP begins. We lift cross-sectional lamellae from the impact sites with a focused-ion beam for further microstructural characterization using electron backscatter diffraction and scanning transmission electron microscopy. Due to the gradients of strain, strain rate, and temperature associated with HDP, heterogeneous microstructures result. The structural evolution processes observed include deformation twinning and multiple dislocation-mediated grain recrystallization mechanisms—geometric dynamic recrystallization (gDRX), discontinuous DRX (dDRX), and meta DRX (mDRX). The higher strains at the interface lead to the most significant structural changes and complex mechanisms. In contrast, there is a gradient to more conventional dislocation plasticity away from the interface (on either the particle or substrate side). These microstructural observations are consistent with the deformation map for copper and extend the observations of impact-induced recrystallization across new regimes of behavior.\n
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\n \n\n \n \n \n \n \n Correlating local chemical and structural order using Geographic Information Systems-based spatial statistics.\n \n \n \n\n\n \n Xu, M., Kumar, A., & LeBeau, J. M\n\n\n \n\n\n\n Ultramicroscopy, 243: 113642. January 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Xu2023-ch,\n  title    = "Correlating local chemical and structural order using Geographic\n              Information Systems-based spatial statistics",\n  author   = "Xu, Michael and Kumar, Abinash and LeBeau, James M",\n  abstract = "Analysis of nanoscale short-range chemical and/or structural\n              order via (scanning) transmission electron microscopy (S/TEM)\n              imaging is fundamentally limited by projection of the three\n              dimensional sample, which averages informational along the beam\n              direction. Extracting statistically significant spatial\n              correlations between the structure and chemistry determined from\n              these two-dimensional datasets thus remains challenging. Here, we\n              apply methods commonly used in Geographic Information Systems\n              (GIS) to determine the spatial correlation between measures of\n              local chemistry and structure from atomic-resolution STEM imaging\n              of a compositionally complex relaxor, Pb(Mg1/3Nb2/3)O3 (PMN). The\n              approach is used to determine the type of ordering present and to\n              quantify the spatial variation of chemical order, oxygen\n              octahedral distortions, and oxygen octahedral tilts. The extent\n              of autocorrelation and inter-feature correlation among these\n              short-range ordered regions are then evaluated through a spatial\n              covariance analysis, showing correlation as a function of\n              distance. The results demonstrate that integrating GIS tools for\n              analyzing microscopy datasets can serve to unravel subtle\n              relationships among chemical and structural features in complex\n              materials that can be hidden when ignoring their spatial\n              distributions.",\n  journal  = "Ultramicroscopy",\n  volume   =  243,\n  pages    = "113642",\n  month    =  jan,\n  year     =  2023,\n  keywords = "Geographic Information Systems; Scanning transmission electron\n              microscopy; Short-range order;LeBeau Group",\n  language = "en",\n  issn     = "0304-3991, 1879-2723",\n  pmid     = "36403389",\n  doi      = "10.1016/j.ultramic.2022.113642"\n}\n\n
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\n Analysis of nanoscale short-range chemical and/or structural order via (scanning) transmission electron microscopy (S/TEM) imaging is fundamentally limited by projection of the three dimensional sample, which averages informational along the beam direction. Extracting statistically significant spatial correlations between the structure and chemistry determined from these two-dimensional datasets thus remains challenging. Here, we apply methods commonly used in Geographic Information Systems (GIS) to determine the spatial correlation between measures of local chemistry and structure from atomic-resolution STEM imaging of a compositionally complex relaxor, Pb(Mg1/3Nb2/3)O3 (PMN). The approach is used to determine the type of ordering present and to quantify the spatial variation of chemical order, oxygen octahedral distortions, and oxygen octahedral tilts. The extent of autocorrelation and inter-feature correlation among these short-range ordered regions are then evaluated through a spatial covariance analysis, showing correlation as a function of distance. The results demonstrate that integrating GIS tools for analyzing microscopy datasets can serve to unravel subtle relationships among chemical and structural features in complex materials that can be hidden when ignoring their spatial distributions.\n
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\n \n\n \n \n \n \n \n A comparison of molecular dynamics potentials used to account for thermal diffuse scattering in multislice simulations.\n \n \n \n\n\n \n Chen, X., Kim, D. S, & LeBeau, J. M\n\n\n \n\n\n\n Ultramicroscopy, 244: 113644. February 2023.\n \n\n\n\n
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@ARTICLE{Chen2023-ot,\n  title    = "A comparison of molecular dynamics potentials used to account for\n              thermal diffuse scattering in multislice simulations",\n  author   = "Chen, Xi and Kim, Dennis S and LeBeau, James M",\n  abstract = "Here we investigate electron scattering simulations with thermal\n              displacements incorporated using molecular dynamics potentials.\n              Specifically, we explore the sensitivity of electron scattering\n              to the phonon band structure, or more explicitly interatomic\n              forces. Silicon serves as the model material where we introduce\n              thermal atomic displacements via empirical and machine-learned\n              molecular dynamics interatomic potentials and compare them to\n              finite-temperature density functional theory interatomic forces.\n              We demonstrate that when molecular dynamics potentials do not\n              sufficiently reproduce the correct phonon band structure,\n              significant errors in the simulated diffraction and image\n              intensities can occur. Moreover, for Si, we find that multislice\n              simulations using machine-learned interatomic potentials are more\n              accurate than empirical ones. In addition to the selected atomic\n              potential, we demonstrate that the sensitivity to the phonon band\n              structure also depends on the crystal zone axis, which can be\n              used to enhance sensitivity to thermal displacements. Finally, we\n              provide a sensitivity analysis with angle-resolved scanning\n              transmission electron microscopy (STEM) to enhance image\n              sensitivity to the details of the phonon band structure.",\n  journal  = "Ultramicroscopy",\n  volume   =  244,\n  pages    = "113644",\n  month    =  feb,\n  year     =  2023,\n  keywords = "Thermal diffuse scattering, Frozen phonon multislice, Phonon band\n              structure;LeBeau Group;Amazon;PECASE;PECASE 2023-2024",\n  language = "en",\n  issn     = "0304-3991, 1879-2723",\n  pmid     = "36410085",\n  doi      = "10.1016/j.ultramic.2022.113644"\n}\n\n
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\n Here we investigate electron scattering simulations with thermal displacements incorporated using molecular dynamics potentials. Specifically, we explore the sensitivity of electron scattering to the phonon band structure, or more explicitly interatomic forces. Silicon serves as the model material where we introduce thermal atomic displacements via empirical and machine-learned molecular dynamics interatomic potentials and compare them to finite-temperature density functional theory interatomic forces. We demonstrate that when molecular dynamics potentials do not sufficiently reproduce the correct phonon band structure, significant errors in the simulated diffraction and image intensities can occur. Moreover, for Si, we find that multislice simulations using machine-learned interatomic potentials are more accurate than empirical ones. In addition to the selected atomic potential, we demonstrate that the sensitivity to the phonon band structure also depends on the crystal zone axis, which can be used to enhance sensitivity to thermal displacements. Finally, we provide a sensitivity analysis with angle-resolved scanning transmission electron microscopy (STEM) to enhance image sensitivity to the details of the phonon band structure.\n
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\n \n\n \n \n \n \n \n Linker-Dependent Stability of Metal-Hydroxide Organic Frameworks for Oxygen Evolution.\n \n \n \n\n\n \n Zheng, D. J, Görlin, M., McCormack, K., Kim, J., Peng, J., Xu, H., Ma, X., LeBeau, J. M, Fischer, R. A, Román-Leshkov, Y., & Shao-Horn, Y.\n\n\n \n\n\n\n Chem. Mater.. June 2023.\n \n\n\n\n
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@ARTICLE{Zheng2023-yh,\n  title     = "{Linker-Dependent} Stability of {Metal-Hydroxide} Organic\n               Frameworks for Oxygen Evolution",\n  author    = "Zheng, Daniel J and G{\\"o}rlin, Mikaela and McCormack, Kaylee\n               and Kim, Junghwa and Peng, Jiayu and Xu, Hongbin and Ma, Xiaoxin\n               and LeBeau, James M and Fischer, Roland A and Rom{\\'a}n-Leshkov,\n               Yuriy and Shao-Horn, Yang",\n  abstract  = "Metal--organic frameworks (MOFs) are periodic organic--inorganic\n               materials that have garnered considerable attention for\n               electrocatalytic applications due to their wide tunability.\n               Metal-hydroxide organic frameworks (MHOFs), a subset of MOFs\n               that combine layered metal hydroxides with organic ligands of\n               various $\\pi$--$\\pi$ stacking energy, have shown promising\n               catalytic functions, such as for the oxygen evolution reaction\n               (OER). The long-term electrochemical stability of these\n               materials for the OER is unfortunately not well understood,\n               which is critical to design practical devices. In this study, we\n               investigated how Ni-based MHOFs composed of two linkers with\n               different $\\pi$--$\\pi$ interaction strength (terephthalate; L1\n               and azobenzene-4,4′-dicarboxylate; L4) change as a function of\n               cycle number and potential for the OER. All MHOFs tested showed\n               significant increases in the number of electrochemically active\n               Ni sites and OER activity when cycled. MHOFs constructed using\n               the linkers with stronger $\\pi$--$\\pi$ stacking energy (L4) were\n               observed to remain intact in bulk with only near-surface\n               transformations to NiOOH2--x-like phases, whereas MHOFs with\n               linkers of weaker $\\pi$--$\\pi$ stacking energy (L1) showed\n               complete reconstruction to NiOOH2--x-like phases. This was\n               confirmed using X-ray diffraction, X-ray absorption\n               spectroscopy, and electron microscopy. Further, in situ\n               characterization using Raman and UV--vis revealed that the\n               presence of stable linkers within the MHOF structure suppresses\n               the Ni2+/Ni(3+$\\delta$)+ redox process. We further identify\n               NiOOH2--x as the OER active phase, while the MHOF phase serves\n               as a precatalyst. We further propose a detailed mechanism for\n               the phase transformation, which provides valuable insights into\n               the future challenges for the design of both stable and\n               catalytically active MOF-based materials for water oxidation.",\n  journal   = "Chem. Mater.",\n  publisher = "American Chemical Society",\n  month     =  jun,\n  year      =  2023,\n  keywords  = "LeBeau Group",\n  issn      = "0897-4756",\n  doi       = "10.1021/acs.chemmater.3c00316"\n}\n\n
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\n Metal–organic frameworks (MOFs) are periodic organic–inorganic materials that have garnered considerable attention for electrocatalytic applications due to their wide tunability. Metal-hydroxide organic frameworks (MHOFs), a subset of MOFs that combine layered metal hydroxides with organic ligands of various $π$–$π$ stacking energy, have shown promising catalytic functions, such as for the oxygen evolution reaction (OER). The long-term electrochemical stability of these materials for the OER is unfortunately not well understood, which is critical to design practical devices. In this study, we investigated how Ni-based MHOFs composed of two linkers with different $π$–$π$ interaction strength (terephthalate; L1 and azobenzene-4,4′-dicarboxylate; L4) change as a function of cycle number and potential for the OER. All MHOFs tested showed significant increases in the number of electrochemically active Ni sites and OER activity when cycled. MHOFs constructed using the linkers with stronger $π$–$π$ stacking energy (L4) were observed to remain intact in bulk with only near-surface transformations to NiOOH2–x-like phases, whereas MHOFs with linkers of weaker $π$–$π$ stacking energy (L1) showed complete reconstruction to NiOOH2–x-like phases. This was confirmed using X-ray diffraction, X-ray absorption spectroscopy, and electron microscopy. Further, in situ characterization using Raman and UV–vis revealed that the presence of stable linkers within the MHOF structure suppresses the Ni2+/Ni(3+$δ$)+ redox process. We further identify NiOOH2–x as the OER active phase, while the MHOF phase serves as a precatalyst. We further propose a detailed mechanism for the phase transformation, which provides valuable insights into the future challenges for the design of both stable and catalytically active MOF-based materials for water oxidation.\n
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\n \n\n \n \n \n \n \n Elucidating Structural Transition Dynamics in the Magnesium Cathode MgCr2O4.\n \n \n \n\n\n \n Kim, J., Anand, S., Gilgenbach, C., Johnson, I. D, Murphy, M., Chen, T., Moy, M., Penn, A., Cabana, J., Ceder, G., Ingram, B. J, & LeBeau, J. M\n\n\n \n\n\n\n Chem. Mater.. October 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Kim2023-qv,\n  title     = "Elucidating Structural Transition Dynamics in the Magnesium\n               Cathode {MgCr2O4}",\n  author    = "Kim, Junghwa and Anand, Shashwat and Gilgenbach, Colin and\n               Johnson, Ian D and Murphy, Megan and Chen, Tina and Moy, Matthew\n               and Penn, Aubrey and Cabana, Jordi and Ceder, Gerbrand and\n               Ingram, Brian J and LeBeau, James M",\n  abstract  = "Multivalent batteries, e.g., those based on magnesium (Mg), are\n               promising candidates for next-generation energy storage due to\n               their high volumetric energy densities and low cost. However,\n               the corresponding ion migration and structural transition\n               mechanisms are often linked and difficult to observe directly.\n               Here, we report the direct investigation of atomic transport\n               pathways of cations in spinel magnesium chromate (MgCr2O4) by\n               using aberration-corrected scanning transmission electron\n               microscopy (STEM). Cr atoms are directly observed to reversibly\n               occupy the otherwise vacant octahedrally coordinated\n               interstitial sites, passing through tetrahedral sites normally\n               occupied by Mg. Furthermore, imaging and electron energy loss\n               spectroscopy show that electron irradiation induces the\n               formation of Mg and O vacancies, facilitating the migration of\n               Cr and leading to an irreversible phase transition. These\n               results demonstrate the ability of STEM to capture the pathway\n               of deleterious point defects that can result in undesirable\n               phase transitions.",\n  journal   = "Chem. Mater.",\n  publisher = "American Chemical Society",\n  month     =  oct,\n  year      =  2023,\n  keywords  = "LeBeau Group",\n  issn      = "0897-4756",\n  doi       = "10.1021/acs.chemmater.3c01219"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Multivalent batteries, e.g., those based on magnesium (Mg), are promising candidates for next-generation energy storage due to their high volumetric energy densities and low cost. However, the corresponding ion migration and structural transition mechanisms are often linked and difficult to observe directly. Here, we report the direct investigation of atomic transport pathways of cations in spinel magnesium chromate (MgCr2O4) by using aberration-corrected scanning transmission electron microscopy (STEM). Cr atoms are directly observed to reversibly occupy the otherwise vacant octahedrally coordinated interstitial sites, passing through tetrahedral sites normally occupied by Mg. Furthermore, imaging and electron energy loss spectroscopy show that electron irradiation induces the formation of Mg and O vacancies, facilitating the migration of Cr and leading to an irreversible phase transition. These results demonstrate the ability of STEM to capture the pathway of deleterious point defects that can result in undesirable phase transitions.\n
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\n \n\n \n \n \n \n \n Machine Learning-Enabled Superior Energy Storage in Ferroelectric Films with a Slush-Like Polar State.\n \n \n \n\n\n \n Yuan, R., Kumar, A., Zhuang, S., Cucciniello, N., Lu, T., Xue, D., Penn, A., Mazza, A. R, Jia, Q., Liu, Y., Xue, D., Li, J., Hu, J., LeBeau, J. M, & Chen, A.\n\n\n \n\n\n\n Nano Lett., 23(11): 4807–4814. June 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Yuan2023-sp,\n  title    = "Machine {Learning-Enabled} Superior Energy Storage in\n              Ferroelectric Films with a {Slush-Like} Polar State",\n  author   = "Yuan, Ruihao and Kumar, Abinash and Zhuang, Shihao and\n              Cucciniello, Nicholas and Lu, Teng and Xue, Deqing and Penn,\n              Aubrey and Mazza, Alessandro R and Jia, Quanxi and Liu, Yun and\n              Xue, Dezhen and Li, Jinshan and Hu, Jia-Mian and LeBeau, James M\n              and Chen, Aiping",\n  abstract = "Heterogeneities in structure and polarization have been employed\n              to enhance the energy storage properties of ferroelectric films.\n              The presence of nonpolar phases, however, weakens the net\n              polarization. Here, we achieve a slush-like polar state with fine\n              domains of different ferroelectric polar phases by narrowing the\n              large combinatorial space of likely candidates using machine\n              learning methods. The formation of the slush-like polar state at\n              the nanoscale in cation-doped BaTiO3 films is simulated by phase\n              field simulation and confirmed by aberration-corrected scanning\n              transmission electron microscopy. The large polarization and the\n              delayed polarization saturation lead to greatly enhanced energy\n              density of 80 J/cm3 and transfer efficiency of 85\\% over a wide\n              temperature range. Such a data-driven design recipe for a\n              slush-like polar state is generally applicable to quickly\n              optimize functionalities of ferroelectric materials.",\n  journal  = "Nano Lett.",\n  volume   =  23,\n  number   =  11,\n  pages    = "4807--4814",\n  month    =  jun,\n  year     =  2023,\n  keywords = "energy storage; ferroelectric films; machine learning; slush-like\n              polar state;LeBeau Group",\n  language = "en",\n  issn     = "1530-6984, 1530-6992",\n  pmid     = "37224193",\n  doi      = "10.1021/acs.nanolett.3c00277"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Heterogeneities in structure and polarization have been employed to enhance the energy storage properties of ferroelectric films. The presence of nonpolar phases, however, weakens the net polarization. Here, we achieve a slush-like polar state with fine domains of different ferroelectric polar phases by narrowing the large combinatorial space of likely candidates using machine learning methods. The formation of the slush-like polar state at the nanoscale in cation-doped BaTiO3 films is simulated by phase field simulation and confirmed by aberration-corrected scanning transmission electron microscopy. The large polarization and the delayed polarization saturation lead to greatly enhanced energy density of 80 J/cm3 and transfer efficiency of 85% over a wide temperature range. Such a data-driven design recipe for a slush-like polar state is generally applicable to quickly optimize functionalities of ferroelectric materials.\n
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\n \n\n \n \n \n \n \n Determination of short-range order in TiVNbHf(Al).\n \n \n \n\n\n \n Xu, M., Wei, S., Tasan, C C., & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 122(18): 181901. May 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Xu2023-hl,\n  title     = "Determination of short-range order in {TiVNbHf(Al})",\n  author    = "Xu, Michael and Wei, Shaolou and Tasan, C Cem and LeBeau, James\n               M",\n  abstract  = "The presence of short-range chemical order can be a key factor\n               in determining the mechanical behavior of metals, but directly\n               and unambiguously determining its distribution in complex\n               concentrated alloy systems can be challenging. Here, we directly\n               identify and quantify chemical order in the globally single\n               phase BCC-TiVNbHf(Al) system using aberration corrected scanning\n               transmission electron microscopy (STEM) paired with spatial\n               statistics methods. To overcome the difficulties of short-range\n               order (SRO) quantification with STEM when the components of an\n               alloy exhibit large atomic number differences and near\n               equiatomic ratios, ``null hypothesis'' tests are used to\n               separate experiment from a random chemical distribution.\n               Experiment is found to deviate from both the case of an ideal\n               random solid solution and a fully ordered structure with\n               statistical significance. We also identify local chemical order\n               in TiVNbHf and confirm and quantify the enhancement of SRO with\n               the addition of Al. These results provide insight into local\n               chemical order in the promising TiVNbHf(Al) refractory alloys\n               while highlighting the utility of spatial statistics in\n               characterizing nanoscale SRO in compositionally complex systems.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "AIP Publishing",\n  volume    =  122,\n  number    =  18,\n  pages     = "181901",\n  month     =  may,\n  year      =  2023,\n  keywords  = "LeBeau Group",\n  language  = "en",\n  issn      = "0003-6951, 1077-3118",\n  doi       = "10.1063/5.0145289"\n}\n\n
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\n The presence of short-range chemical order can be a key factor in determining the mechanical behavior of metals, but directly and unambiguously determining its distribution in complex concentrated alloy systems can be challenging. Here, we directly identify and quantify chemical order in the globally single phase BCC-TiVNbHf(Al) system using aberration corrected scanning transmission electron microscopy (STEM) paired with spatial statistics methods. To overcome the difficulties of short-range order (SRO) quantification with STEM when the components of an alloy exhibit large atomic number differences and near equiatomic ratios, ``null hypothesis'' tests are used to separate experiment from a random chemical distribution. Experiment is found to deviate from both the case of an ideal random solid solution and a fully ordered structure with statistical significance. We also identify local chemical order in TiVNbHf and confirm and quantify the enhancement of SRO with the addition of Al. These results provide insight into local chemical order in the promising TiVNbHf(Al) refractory alloys while highlighting the utility of spatial statistics in characterizing nanoscale SRO in compositionally complex systems.\n
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\n \n\n \n \n \n \n \n Tunable artificial relaxor behavior in [BaTiO_\\3\\]_\\m\\/[BaZrO_\\3\\]_\\n\\ superlattices.\n \n \n \n\n\n \n Tian, Z., Xu, M., Kim, J., Pan, H., Lou, D., Huang, X., LeBeau, J. M, & Martin, L. W\n\n\n \n\n\n\n Phys. Rev. Lett., 130(26): 266801. June 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Tian2023-vp,\n  title     = "Tunable artificial relaxor behavior in\n               [{BaTiO\\_\\{3\\}]\\_\\{m\\}/[BaZrO\\_\\{3\\}]\\_\\{n\\}} superlattices",\n  author    = "Tian, Zishen and Xu, Michael and Kim, Jieun and Pan, Hao and\n               Lou, Djamila and Huang, Xiaoxi and LeBeau, James M and Martin,\n               Lane W",\n  abstract  = "[BaTiO\\_\\{3\\}]\\_\\{m\\}/[BaZrO\\_\\{3\\}]\\_\\{n\\} (m, n=4-12)\n               superlattices are used to demonstrate the fabrication and\n               deterministic control of an artificial relaxor. X-ray\n               diffraction and atomic-resolution imaging studies confirm the\n               production of high-quality heterostructures. With decreasing\n               BaTiO\\_\\{3\\} layer thickness, dielectric measurements reveal\n               systematically lower dielectric-maximum temperatures, while\n               hysteresis loops and third-harmonic nonlinearity studies suggest\n               a transition from ferroelectriclike to relaxorlike behavior\n               driven by tuning the random-field strength. This system provides\n               a novel platform for studying the size effect and interaction\n               length scale of the nanoscale-polar structures in relaxors.",\n  journal   = "Phys. Rev. Lett.",\n  publisher = "APS",\n  volume    =  130,\n  number    =  26,\n  pages     = "266801",\n  month     =  jun,\n  year      =  2023,\n  keywords  = "LeBeau Group",\n  language  = "en",\n  issn      = "0031-9007, 1079-7114",\n  pmid      = "37450818",\n  doi       = "10.1103/PhysRevLett.130.266801"\n}\n\n
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\n [BaTiO_\\3\\]_\\m\\/[BaZrO_\\3\\]_\\n\\ (m, n=4-12) superlattices are used to demonstrate the fabrication and deterministic control of an artificial relaxor. X-ray diffraction and atomic-resolution imaging studies confirm the production of high-quality heterostructures. With decreasing BaTiO_\\3\\ layer thickness, dielectric measurements reveal systematically lower dielectric-maximum temperatures, while hysteresis loops and third-harmonic nonlinearity studies suggest a transition from ferroelectriclike to relaxorlike behavior driven by tuning the random-field strength. This system provides a novel platform for studying the size effect and interaction length scale of the nanoscale-polar structures in relaxors.\n
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\n \n\n \n \n \n \n \n Thermodynamic assessment within the Zr–B–C–O quaternary system.\n \n \n \n\n\n \n Pham, D., Gai, F., Rochester, J., Dycus, J. H, LeBeau, J. M, Manga, V. R., & Corral, E. L\n\n\n \n\n\n\n J. Am. Ceram. Soc., 106(5): 3127–3140. May 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Pham2023-zn,\n  title     = "Thermodynamic assessment within the {Zr--B--C--O} quaternary\n               system",\n  author    = "Pham, David and Gai, Fangyuan and Rochester, Jacob and Dycus,\n               Joseph H and LeBeau, James M and Manga, Venkateswara Rao and\n               Corral, Erica L",\n  abstract  = "Abstract Thermodynamic modeling of Zr?B?C?O quaternary system is\n               conducted within the CALPHAD framework by employing data\n               obtained from first-principle calculations and literature. The\n               lower order binary B?O is assessed in this work by estimating\n               the thermodynamic properties of stable solid phases of B2O3 and\n               B6O and by estimating the gas and liquid phases. First-principle\n               calculations, in conjunction with special quasirandom structure\n               were used to predict enthalpies of mixing for the ternary\n               solid-solution phase of FCC-Zr(C, O). The calculated results\n               were used to optimize the model parameters pertaining to the\n               cubic phase, which is described by a two-sublattice model. The\n               modeled Zr?C?O ternary phase diagrams calculated at 1923 and\n               2273 K under ambient pressure and 4 Pa, respectively, are in\n               agreement with experimental phase diagrams.",\n  journal   = "J. Am. Ceram. Soc.",\n  publisher = "Wiley",\n  volume    =  106,\n  number    =  5,\n  pages     = "3127--3140",\n  month     =  may,\n  year      =  2023,\n  keywords  = "LeBeau Group",\n  copyright = "http://onlinelibrary.wiley.com/termsAndConditions\\#vor",\n  language  = "en",\n  issn      = "0002-7820, 1551-2916",\n  doi       = "10.1111/jace.18958"\n}\n\n
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\n Abstract Thermodynamic modeling of Zr?B?C?O quaternary system is conducted within the CALPHAD framework by employing data obtained from first-principle calculations and literature. The lower order binary B?O is assessed in this work by estimating the thermodynamic properties of stable solid phases of B2O3 and B6O and by estimating the gas and liquid phases. First-principle calculations, in conjunction with special quasirandom structure were used to predict enthalpies of mixing for the ternary solid-solution phase of FCC-Zr(C, O). The calculated results were used to optimize the model parameters pertaining to the cubic phase, which is described by a two-sublattice model. The modeled Zr?C?O ternary phase diagrams calculated at 1923 and 2273 K under ambient pressure and 4 Pa, respectively, are in agreement with experimental phase diagrams.\n
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\n \n\n \n \n \n \n \n Sn-modified BaTiO3 thin film with enhanced polarization.\n \n \n \n\n\n \n Nunn, W., Kumar, A., Zu, R., Nebgen, B., Yu, S., Kamath Manjeshwar, A., Gopalan, V., LeBeau, J. M, James, R. D, & Jalan, B.\n\n\n \n\n\n\n J. Vac. Sci. Technol. A, 41(2): 022701. March 2023.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Nunn2023-nh,\n  title     = "Sn-modified {BaTiO3} thin film with enhanced polarization",\n  author    = "Nunn, William and Kumar, Abinash and Zu, Rui and Nebgen, Bailey\n               and Yu, Shukai and Kamath Manjeshwar, Anusha and Gopalan,\n               Venkatraman and LeBeau, James M and James, Richard D and Jalan,\n               Bharat",\n  abstract  = "Hybrid molecular beam epitaxy (MBE) growth of Sn-modified BaTiO3\n               films was realized with varying domain structures and crystal\n               symmetries across the entire composition space. Macroscopic and\n               microscopic structures and the crystal symmetry of these thin\n               films were determined using a combination of optical second\n               harmonic generation (SHG) polarimetry and scanning transmission\n               electron microscopy (STEM). SHG polarimetry revealed a variation\n               in the global crystal symmetry of the films from tetragonal\n               (P4mm) to cubic (Pm3?m) across the composition range, x?=?0 to 1\n               in BaTi1?xSnxO3 (BTSO). STEM imaging shows that the long-range\n               polar order observed when the Sn content is low (x?=?0.09)\n               transformed to a short-range polar order as the Sn content\n               increased (x?=?0.48). Consistent with atomic displacement\n               measurements from STEM, the largest polarization was obtained at\n               the lowest Sn content of x?=?0.09 in Sn-modified BaTiO3 as\n               determined by SHG. These results agree with recent bulk ceramic\n               reports and further identify this material system as a potential\n               replacement for Pb-containing relaxor-based thin film devices.",\n  journal   = "J. Vac. Sci. Technol. A",\n  publisher = "American Vacuum Society",\n  volume    =  41,\n  number    =  2,\n  pages     = "022701",\n  month     =  mar,\n  year      =  2023,\n  keywords  = "LeBeau Group",\n  issn      = "0734-2101",\n  doi       = "10.1116/6.0002208"\n}\n\n
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\n Hybrid molecular beam epitaxy (MBE) growth of Sn-modified BaTiO3 films was realized with varying domain structures and crystal symmetries across the entire composition space. Macroscopic and microscopic structures and the crystal symmetry of these thin films were determined using a combination of optical second harmonic generation (SHG) polarimetry and scanning transmission electron microscopy (STEM). SHG polarimetry revealed a variation in the global crystal symmetry of the films from tetragonal (P4mm) to cubic (Pm3?m) across the composition range, x?=?0 to 1 in BaTi1?xSnxO3 (BTSO). STEM imaging shows that the long-range polar order observed when the Sn content is low (x?=?0.09) transformed to a short-range polar order as the Sn content increased (x?=?0.48). Consistent with atomic displacement measurements from STEM, the largest polarization was obtained at the lowest Sn content of x?=?0.09 in Sn-modified BaTiO3 as determined by SHG. These results agree with recent bulk ceramic reports and further identify this material system as a potential replacement for Pb-containing relaxor-based thin film devices.\n
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\n \n\n \n \n \n \n \n Towards Augmented Microscopy with Reinforcement Learning-Enhanced Workflows.\n \n \n \n\n\n \n Xu, M., Kumar, A., & LeBeau, J. M\n\n\n \n\n\n\n Microsc. Microanal., 28(6): 1–9. September 2022.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Xu2022-fd,\n  title    = "Towards Augmented Microscopy with Reinforcement\n              {Learning-Enhanced} Workflows",\n  author   = "Xu, Michael and Kumar, Abinash and LeBeau, James M",\n  abstract = "Here, we report a case study implementation of reinforcement\n              learning (RL) to automate operations in the scanning transmission\n              electron microscopy workflow. To do so, we design a virtual,\n              prototypical RL environment to test and develop a network to\n              autonomously align the electron beam position without prior\n              knowledge. Using this simulator, we evaluate the impact of\n              environment design and algorithm hyperparameters on alignment\n              accuracy and learning convergence, showing robust convergence\n              across a wide hyperparameter space. Additionally, we deploy a\n              successful model on the microscope to validate the approach and\n              demonstrate the value of designing appropriate virtual\n              environments. Consistent with simulated results, the\n              on-microscope RL model achieves convergence to the goal alignment\n              after minimal training. Overall, the results highlight that by\n              taking advantage of RL, microscope operations can be automated\n              without the need for extensive algorithm design, taking another\n              step toward augmenting electron microscopy with machine learning\n              methods.",\n  journal  = "Microsc. Microanal.",\n  volume   =  28,\n  number   =  6,\n  pages    = "1--9",\n  month    =  sep,\n  year     =  2022,\n  keywords = "automated microscopy; reinforcement learning; scanning\n              transmission electron microscopy;LeBeau Group;Amazon",\n  language = "en",\n  issn     = "1431-9276, 1435-8115",\n  pmid     = "36062363",\n  arxivid  = "2208.02865",\n  doi      = "10.1017/S1431927622012193"\n}\n\n
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\n Here, we report a case study implementation of reinforcement learning (RL) to automate operations in the scanning transmission electron microscopy workflow. To do so, we design a virtual, prototypical RL environment to test and develop a network to autonomously align the electron beam position without prior knowledge. Using this simulator, we evaluate the impact of environment design and algorithm hyperparameters on alignment accuracy and learning convergence, showing robust convergence across a wide hyperparameter space. Additionally, we deploy a successful model on the microscope to validate the approach and demonstrate the value of designing appropriate virtual environments. Consistent with simulated results, the on-microscope RL model achieves convergence to the goal alignment after minimal training. Overall, the results highlight that by taking advantage of RL, microscope operations can be automated without the need for extensive algorithm design, taking another step toward augmenting electron microscopy with machine learning methods.\n
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\n \n\n \n \n \n \n \n Antisite defects stabilized by antiphase boundaries in YFeO$_{3}$ thin films.\n \n \n \n\n\n \n Kumar, A., Klyukin, K., Ning, S., Ozsoy-Keskinbora, C., Ovsyanko, M., van Uden, F., Krijnen, R., Yildiz, B., Ross, C. A, & LeBeau, J. M\n\n\n \n\n\n\n Adv. Funct. Mater., 32(9): 2107017. February 2022.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Kumar2022-gs,\n  title     = "Antisite defects stabilized by antiphase boundaries in\n               {YFeO$_{3}$} thin films",\n  author    = "Kumar, Abinash and Klyukin, Konstantin and Ning, Shuai and\n               Ozsoy-Keskinbora, Cigdem and Ovsyanko, Mikhail and van Uden,\n               Felix and Krijnen, Ruud and Yildiz, Bilge and Ross, Caroline A\n               and LeBeau, James M",\n  abstract  = "AbstractYFeO3 thin films are a recent addition to the family of\n               multiferroic orthoferrites where YFe antisite defects and strain\n               have been shown to introduce polar displacements while retaining\n               magnetic properties. Complete control of the multiferroic\n               properties, however, necessitates knowledge of the defects\n               present and their potential role in modifying behavior. Here,\n               the structure and chemistry of antiphase boundaries in Y‐rich\n               multiferroic YFeO3 thin films are reported using aberration\n               corrected scanning transmission electron microscopy combined\n               with atomic resolution energy dispersive X‐ray spectroscopy. It\n               is found that FeY antisites, which are not stable in the Y‐rich\n               film bulk, periodically arrange along antiphase boundaries due\n               to changes in the local structural environment. Using density\n               functional theory, it is shown that the antiphase boundaries are\n               polar and bi‐stable, where the presence of FeY antisites\n               significantly decreases the switching barrier. These results\n               highlight how planar defects, such as antiphase boundaries, can\n               stabilize point defects that would otherwise not be expected to\n               form within the structure.",\n  journal   = "Adv. Funct. Mater.",\n  publisher = "Wiley",\n  volume    =  32,\n  number    =  9,\n  pages     = "2107017",\n  month     =  feb,\n  year      =  2022,\n  keywords  = "LeBeau Group;DHS proposal;Amazon",\n  copyright = "http://onlinelibrary.wiley.com/termsAndConditions\\#vor",\n  language  = "en",\n  issn      = "1616-301X, 1616-3028",\n  doi       = "10.1002/adfm.202107017"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n AbstractYFeO3 thin films are a recent addition to the family of multiferroic orthoferrites where YFe antisite defects and strain have been shown to introduce polar displacements while retaining magnetic properties. Complete control of the multiferroic properties, however, necessitates knowledge of the defects present and their potential role in modifying behavior. Here, the structure and chemistry of antiphase boundaries in Y‐rich multiferroic YFeO3 thin films are reported using aberration corrected scanning transmission electron microscopy combined with atomic resolution energy dispersive X‐ray spectroscopy. It is found that FeY antisites, which are not stable in the Y‐rich film bulk, periodically arrange along antiphase boundaries due to changes in the local structural environment. Using density functional theory, it is shown that the antiphase boundaries are polar and bi‐stable, where the presence of FeY antisites significantly decreases the switching barrier. These results highlight how planar defects, such as antiphase boundaries, can stabilize point defects that would otherwise not be expected to form within the structure.\n
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\n \n\n \n \n \n \n \n Tuning surface acidity of mixed conducting electrodes: Recovery of Si-induced degradation of oxygen exchange rate and area specific resistance.\n \n \n \n\n\n \n Seo, H. G., Staerz, A., Kim, D. S, LeBeau, J. M, & Tuller, H. L\n\n\n \n\n\n\n Adv. Mater.,e2208182. December 2022.\n \n\n\n\n
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@ARTICLE{Seo2022-lo,\n  title     = "Tuning surface acidity of mixed conducting electrodes: Recovery\n               of Si-induced degradation of oxygen exchange rate and area\n               specific resistance",\n  author    = "Seo, Han Gil and Staerz, Anna and Kim, Dennis S and LeBeau,\n               James M and Tuller, Harry L",\n  abstract  = "Metal oxides are an important class of functional materials, and\n               for many applications, ranging from solid oxide\n               fuel/electrolysis cells, oxygen permeation membranes, and oxygen\n               storage materials to gas sensors (semiconducting and\n               electrolytic) and catalysts, the interaction between the surface\n               and oxygen in the gas phase is central. Ubiquitous Si-impurities\n               are known to impede this interaction, commonly attributed to the\n               formation of glassy blocking layers on the surface. Here, we\n               examine the surface oxygen exchange coefficient (kchem ) of\n               Pr0.1 Ce0.9 O2-$\\delta$ (PCO), a model mixed ionic electronic\n               conductor, via electrical conductivity relaxation measurements,\n               and the area-specific resistance (ASR) by electrochemical\n               impedance spectroscopy. We demonstrate that even low silica\n               levels, introduced by infiltration, depress kchem by a factor\n               4,000, while the ASR increases 40-fold and attribute this to its\n               acidity relative to that of PCO. We further show the ability to\n               fully regenerate the poisoned surface by the subsequent addition\n               of basic Ca- or Li-species. This ability to not only recover\n               Si-poisoned surfaces by tuning the relative surface acidity of\n               an oxide surface, but subsequently outperform the pre-poisoned\n               response, promises to extend the operating life of materials and\n               devices for which the catalytic oxygen/solid interface reaction\n               is central. This article is protected by copyright. All rights\n               reserved.",\n  journal   = "Adv. Mater.",\n  publisher = "Wiley",\n  pages     = "e2208182",\n  month     =  dec,\n  year      =  2022,\n  keywords  = "Pr0.1Ce0.9O2-$\\delta$; Relative acidity; mixed ionic electronic\n               conducting oxide; oxygen exchange kinetics; silica\n               poisoning;LeBeau Group;PECASE;PFIB;PECASE 2023-2024",\n  copyright = "http://onlinelibrary.wiley.com/termsAndConditions\\#vor",\n  language  = "en",\n  issn      = "0935-9648, 1521-4095",\n  pmid      = "36461730",\n  doi       = "10.1002/adma.202208182"\n}\n\n
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\n Metal oxides are an important class of functional materials, and for many applications, ranging from solid oxide fuel/electrolysis cells, oxygen permeation membranes, and oxygen storage materials to gas sensors (semiconducting and electrolytic) and catalysts, the interaction between the surface and oxygen in the gas phase is central. Ubiquitous Si-impurities are known to impede this interaction, commonly attributed to the formation of glassy blocking layers on the surface. Here, we examine the surface oxygen exchange coefficient (kchem ) of Pr0.1 Ce0.9 O2-$δ$ (PCO), a model mixed ionic electronic conductor, via electrical conductivity relaxation measurements, and the area-specific resistance (ASR) by electrochemical impedance spectroscopy. We demonstrate that even low silica levels, introduced by infiltration, depress kchem by a factor 4,000, while the ASR increases 40-fold and attribute this to its acidity relative to that of PCO. We further show the ability to fully regenerate the poisoned surface by the subsequent addition of basic Ca- or Li-species. This ability to not only recover Si-poisoned surfaces by tuning the relative surface acidity of an oxide surface, but subsequently outperform the pre-poisoned response, promises to extend the operating life of materials and devices for which the catalytic oxygen/solid interface reaction is central. This article is protected by copyright. All rights reserved.\n
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\n \n\n \n \n \n \n \n Magnetoelectric vertically aligned nanocomposite of YFeO $_{3}$ and CoFe $_{2}$ O $_{4}$.\n \n \n \n\n\n \n Kumar, A., Ning, S., Su, T., Cho, E., LeBeau, J. M, & Ross, C. A\n\n\n \n\n\n\n Adv. Electron. Mater., 8(6): 2200036. June 2022.\n \n\n\n\n
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@ARTICLE{Kumar2022-rm,\n  title     = "Magnetoelectric vertically aligned nanocomposite of {YFeO}\n               $_{3}$ and {CoFe} $_{2}$ {O} $_{4}$",\n  author    = "Kumar, Abinash and Ning, Shuai and Su, Tingyu and Cho, Eunsoo\n               and LeBeau, James M and Ross, Caroline A",\n  abstract  = "Abstract Self-assembled two-phase vertically aligned\n               nanocomposites consisting of ferromagnetic pillars embedded in a\n               ferroelectric matrix provide an attractive geometry for\n               observing magnetoelectric coupling based on the strain-coupled\n               magnetostrictive and piezoelectric effects at the interfaces. In\n               perovskite-spinel nanocomposites the ferroelectric phase\n               typically consists of BiFeO3, BaTiO3 or Pb(Zr,Ti)O3. Here, the\n               ferroelectric phase is Y-rich YFeO3 which exhibits\n               ferroelectricity originating from the local inversion symmetry\n               breaking caused by YFe antisite defects. Coherent interfaces\n               observed between Y-rich YFeO3 and a magnetic spinel CoFe2O4 in a\n               vertically aligned nanocomposite enable strain-mediated\n               magnetoelectric coupling at room temperature, confirming the\n               ferroelectricity and piezoelectricity in Y-rich YFeO3 and\n               extending the range of magnetoelectric nanocomposite\n               compositions.",\n  journal   = "Adv. Electron. Mater.",\n  publisher = "Wiley",\n  volume    =  8,\n  number    =  6,\n  pages     = "2200036",\n  month     =  jun,\n  year      =  2022,\n  keywords  = "LeBeau Group",\n  copyright = "http://onlinelibrary.wiley.com/termsAndConditions\\#vor",\n  language  = "en",\n  issn      = "2199-160X",\n  doi       = "10.1002/aelm.202200036"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Abstract Self-assembled two-phase vertically aligned nanocomposites consisting of ferromagnetic pillars embedded in a ferroelectric matrix provide an attractive geometry for observing magnetoelectric coupling based on the strain-coupled magnetostrictive and piezoelectric effects at the interfaces. In perovskite-spinel nanocomposites the ferroelectric phase typically consists of BiFeO3, BaTiO3 or Pb(Zr,Ti)O3. Here, the ferroelectric phase is Y-rich YFeO3 which exhibits ferroelectricity originating from the local inversion symmetry breaking caused by YFe antisite defects. Coherent interfaces observed between Y-rich YFeO3 and a magnetic spinel CoFe2O4 in a vertically aligned nanocomposite enable strain-mediated magnetoelectric coupling at room temperature, confirming the ferroelectricity and piezoelectricity in Y-rich YFeO3 and extending the range of magnetoelectric nanocomposite compositions.\n
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\n \n\n \n \n \n \n \n Promoting mechanistic understanding of lithium deposition and solid‐electrolyte interphase (SEI) formation using advanced characterization and simulation methods: Recent progress, limitations, and future perspectives.\n \n \n \n\n\n \n Xu, Y., Dong, K., Jie, Y., Adelhelm, P., Chen, Y., Xu, L., Yu, P., Kim, J., Kochovski, Z., Yu, Z., Li, W., LeBeau, J. M, Shao-Horn, Y., Cao, R., Jiao, S., Cheng, T., Manke, I., & Lu, Y.\n\n\n \n\n\n\n Adv. Energy Mater., 12(19): 2200398. May 2022.\n \n\n\n\n
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@ARTICLE{Xu2022-hf,\n  title     = "Promoting mechanistic understanding of lithium deposition and\n               solid‐electrolyte interphase ({SEI}) formation using advanced\n               characterization and simulation methods: Recent progress,\n               limitations, and future perspectives",\n  author    = "Xu, Yaolin and Dong, Kang and Jie, Yulin and Adelhelm, Philipp\n               and Chen, Yawei and Xu, Liang and Yu, Peiping and Kim, Junghwa\n               and Kochovski, Zdravko and Yu, Zhilong and Li, Wanxia and\n               LeBeau, James M and Shao-Horn, Yang and Cao, Ruiguo and Jiao,\n               Shuhong and Cheng, Tao and Manke, Ingo and Lu, Yan",\n  abstract  = "Abstract In recent years, due to its great promise in boosting\n               the energy density of lithium batteries for future energy\n               storage, research on the Li metal anode, as an alternative to\n               the graphite anode in Li-ion batteries, has gained significant\n               momentum. However, the practical use of Li metal anodes has been\n               plagued by unstable Li (re)deposition and poor cyclability.\n               Although tremendous efforts have been devoted to the\n               stabilization of Li metal anodes, the mechanisms of\n               electrochemical (re-)deposition/dissolution of Li and\n               solid-electrolyte-interphase (SEI) formation remain elusive.\n               This article highlights the recent mechanistic understandings\n               and observations of Li deposition/dissolution and SEI formation\n               achieved from advanced characterization techniques and\n               simulation methods, and discusses major limitations and open\n               questions in these processes. In particular, the authors provide\n               their perspectives on advanced and emerging/potential methods\n               for obtaining new insights into these questions. In addition,\n               they give an outlook into cutting-edge interdisciplinary\n               research topics for Li metal anodes. It pushes beyond the\n               current knowledge and is expected to accelerate development\n               toward a more in-depth and comprehensive understanding, in order\n               to guide future research on Li metal anodes toward practical\n               application.",\n  journal   = "Adv. Energy Mater.",\n  publisher = "Wiley",\n  volume    =  12,\n  number    =  19,\n  pages     = "2200398",\n  month     =  may,\n  year      =  2022,\n  keywords  = "LeBeau Group",\n  copyright = "http://creativecommons.org/licenses/by/4.0/",\n  language  = "en",\n  issn      = "1614-6832, 1614-6840",\n  doi       = "10.1002/aenm.202200398"\n}\n\n
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\n Abstract In recent years, due to its great promise in boosting the energy density of lithium batteries for future energy storage, research on the Li metal anode, as an alternative to the graphite anode in Li-ion batteries, has gained significant momentum. However, the practical use of Li metal anodes has been plagued by unstable Li (re)deposition and poor cyclability. Although tremendous efforts have been devoted to the stabilization of Li metal anodes, the mechanisms of electrochemical (re-)deposition/dissolution of Li and solid-electrolyte-interphase (SEI) formation remain elusive. This article highlights the recent mechanistic understandings and observations of Li deposition/dissolution and SEI formation achieved from advanced characterization techniques and simulation methods, and discusses major limitations and open questions in these processes. In particular, the authors provide their perspectives on advanced and emerging/potential methods for obtaining new insights into these questions. In addition, they give an outlook into cutting-edge interdisciplinary research topics for Li metal anodes. It pushes beyond the current knowledge and is expected to accelerate development toward a more in-depth and comprehensive understanding, in order to guide future research on Li metal anodes toward practical application.\n
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\n \n\n \n \n \n \n \n Oxide layer delamination: An energy dissipation mechanism during high-velocity microparticle impacts.\n \n \n \n\n\n \n Tiamiyu, A. A, Chen, X., Pang, E. L, Sun, Y., Lienhard, J., LeBeau, J. M, Nelson, K. A, & Schuh, C. A\n\n\n \n\n\n\n Appl. Surf. Sci., 574: 151673. February 2022.\n \n\n\n\n
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@ARTICLE{Tiamiyu2022-mc,\n  title    = "Oxide layer delamination: An energy dissipation mechanism during\n              high-velocity microparticle impacts",\n  author   = "Tiamiyu, Ahmed A and Chen, Xi and Pang, Edward L and Sun, Yuchen\n              and Lienhard, Jasper and LeBeau, James M and Nelson, Keith A and\n              Schuh, Christopher A",\n  abstract = "The break-up of microparticle surface oxides is needed to\n              generate a clean metal-metal contact for metallurgical bonding\n              during impact events such as seen in cold-spray. However, the\n              mechanism by which this occurs is not clear. Using a\n              laser-induced particle impact tester, we conduct site-specific\n              experiment of single Cu microparticle impacts on a polished Cu\n              substrate and characterize the impact sites. We observe that\n              oxide layers on the particles begin to delaminate at velocities\n              high enough to cause jetting of the substrate around the\n              periphery of the impact site. We show that the energy cost of\n              such delamination is ∼30\\% of the energy needed to slow and stop\n              particle as it bonds to the substrate, with the remainder being\n              associated with the jetting process and bonding itself. At higher\n              velocities, the oxide barrier is broken up to permit\n              metallurgical bonding. Closer to the particle south-pole where\n              hoop strain is low, oxide layers break up with few gaps and thus\n              no metallurgical bonding is observed. Away from the south-pole\n              where larger strains develop, oxide breakup permits intermittent\n              bonding by the extrusion of bare metal into the gaps between\n              oxide islands. These observations provide new insights towards\n              understanding impact-induced metallurgical bonding during\n              cold-spray process.",\n  journal  = "Appl. Surf. Sci.",\n  volume   =  574,\n  pages    = "151673",\n  month    =  feb,\n  year     =  2022,\n  keywords = "Cold spray; High-velocity impacts; Jetting; Metallurgical\n              bonding; Oxide layer delamination; Energy dissipation\n              mechanism;LeBeau Group;AFOSR;PECASE",\n  issn     = "0169-4332",\n  doi      = "10.1016/j.apsusc.2021.151673"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n The break-up of microparticle surface oxides is needed to generate a clean metal-metal contact for metallurgical bonding during impact events such as seen in cold-spray. However, the mechanism by which this occurs is not clear. Using a laser-induced particle impact tester, we conduct site-specific experiment of single Cu microparticle impacts on a polished Cu substrate and characterize the impact sites. We observe that oxide layers on the particles begin to delaminate at velocities high enough to cause jetting of the substrate around the periphery of the impact site. We show that the energy cost of such delamination is ∼30% of the energy needed to slow and stop particle as it bonds to the substrate, with the remainder being associated with the jetting process and bonding itself. At higher velocities, the oxide barrier is broken up to permit metallurgical bonding. Closer to the particle south-pole where hoop strain is low, oxide layers break up with few gaps and thus no metallurgical bonding is observed. Away from the south-pole where larger strains develop, oxide breakup permits intermittent bonding by the extrusion of bare metal into the gaps between oxide islands. These observations provide new insights towards understanding impact-induced metallurgical bonding during cold-spray process.\n
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\n \n\n \n \n \n \n \n Additional hindrances to metallurgical bonding from impurities during microparticle impact.\n \n \n \n\n\n \n Chen, X., Tiamiyu, A. A, Schuh, C. A, & LeBeau, J. M\n\n\n \n\n\n\n Surf. Coat. Technol., 433: 128114. March 2022.\n \n\n\n\n
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@ARTICLE{Chen2022-ul,\n  title    = "Additional hindrances to metallurgical bonding from impurities\n              during microparticle impact",\n  author   = "Chen, Xi and Tiamiyu, Ahmed A and Schuh, Christopher A and\n              LeBeau, James M",\n  abstract = "Successful cold spray processing requires the formation of\n              metallurgical bonds at the interface between particle impact\n              sites and the substrate. While surface contamination on either\n              the particle or substrate can interfere with metallurgical\n              bonding, the details of particle/substrate interface chemistry\n              are usually obscured or lost during the nanoseconds-long particle\n              impact process. To provide a direct, detailed account of\n              particle-substrate interfacial chemistry, we perform post-mortem\n              scanning transmission electron microscopy and spectroscopy of\n              impact sites of single copper microparticles, launched with a\n              laser-induced particle impact tester, on a copper substrate. In\n              addition to native oxides, we find that amorphous carbon and\n              spherical copper oxide dispersoids are also present near/at the\n              interface. Further, these features are found to influence\n              metallurgical bonding. These results offer additional\n              considerations for optimizing the quality of the cold spray\n              deposition process.",\n  journal  = "Surf. Coat. Technol.",\n  volume   =  433,\n  pages    = "128114",\n  month    =  mar,\n  year     =  2022,\n  keywords = "Cold spray processing; Surface impurities; Scanning transmission\n              electron microscopy; Oxide dispersoids; Metallurgical bonding;\n              Amorphous carbon;LeBeau Group;AFOSR;PECASE;PECASE 2023-2024",\n  issn     = "0257-8972",\n  doi      = "10.1016/j.surfcoat.2022.128114"\n}\n\n
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\n Successful cold spray processing requires the formation of metallurgical bonds at the interface between particle impact sites and the substrate. While surface contamination on either the particle or substrate can interfere with metallurgical bonding, the details of particle/substrate interface chemistry are usually obscured or lost during the nanoseconds-long particle impact process. To provide a direct, detailed account of particle-substrate interfacial chemistry, we perform post-mortem scanning transmission electron microscopy and spectroscopy of impact sites of single copper microparticles, launched with a laser-induced particle impact tester, on a copper substrate. In addition to native oxides, we find that amorphous carbon and spherical copper oxide dispersoids are also present near/at the interface. Further, these features are found to influence metallurgical bonding. These results offer additional considerations for optimizing the quality of the cold spray deposition process.\n
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\n \n\n \n \n \n \n \n Exsolution-Driven Surface Transformation in the Host Oxide.\n \n \n \n\n\n \n Wang, J., Kumar, A., Wardini, J. L, Zhang, Z., Zhou, H., Crumlin, E. J, Sadowski, J. T, Woller, K. B, Bowman, W. J, LeBeau, J. M, & Yildiz, B.\n\n\n \n\n\n\n Nano Lett., 22(13): 5401–5408. July 2022.\n \n\n\n\n
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@ARTICLE{Wang2022-ve,\n  title    = "{Exsolution-Driven} Surface Transformation in the Host Oxide",\n  author   = "Wang, Jiayue and Kumar, Abinash and Wardini, Jenna L and Zhang,\n              Zhan and Zhou, Hua and Crumlin, Ethan J and Sadowski, Jerzy T and\n              Woller, Kevin B and Bowman, William J and LeBeau, James M and\n              Yildiz, Bilge",\n  abstract = "Exsolution synthesizes self-assembled metal nanoparticle\n              catalysts via phase precipitation. An overlooked aspect in this\n              method thus far is how exsolution affects the host oxide surface\n              chemistry and structure. Such information is critical as the\n              oxide itself can also contribute to the overall catalytic\n              activity. Combining X-ray and electron probes, we investigated\n              the surface transformation of thin-film SrTi0.65Fe0.35O3 during\n              Fe0 exsolution. We found that exsolution generates a highly\n              Fe-deficient near-surface layer of about 2 nm thick. Moreover,\n              the originally single-crystalline oxide near-surface region\n              became partially polycrystalline after exsolution. Such drastic\n              transformations at the surface of the oxide are important because\n              the exsolution-induced nonstoichiometry and grain boundaries can\n              alter the oxide ion transport and oxygen exchange kinetics and,\n              hence, the catalytic activity toward water splitting or hydrogen\n              oxidation reactions. These findings highlight the need to\n              consider the exsolved oxide surface, in addition to the metal\n              nanoparticles, in designing the exsolved nanocatalysts.",\n  journal  = "Nano Lett.",\n  volume   =  22,\n  number   =  13,\n  pages    = "5401--5408",\n  month    =  jul,\n  year     =  2022,\n  keywords = "exsolution; nanoparticles; perovskite oxides; self-assembly;\n              surface transformation;Velion Pubs;LeBeau Group;DHS proposal",\n  language = "en",\n  issn     = "1530-6984, 1530-6992",\n  pmid     = "35771744",\n  doi      = "10.1021/acs.nanolett.2c01439"\n}\n\n
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\n Exsolution synthesizes self-assembled metal nanoparticle catalysts via phase precipitation. An overlooked aspect in this method thus far is how exsolution affects the host oxide surface chemistry and structure. Such information is critical as the oxide itself can also contribute to the overall catalytic activity. Combining X-ray and electron probes, we investigated the surface transformation of thin-film SrTi0.65Fe0.35O3 during Fe0 exsolution. We found that exsolution generates a highly Fe-deficient near-surface layer of about 2 nm thick. Moreover, the originally single-crystalline oxide near-surface region became partially polycrystalline after exsolution. Such drastic transformations at the surface of the oxide are important because the exsolution-induced nonstoichiometry and grain boundaries can alter the oxide ion transport and oxygen exchange kinetics and, hence, the catalytic activity toward water splitting or hydrogen oxidation reactions. These findings highlight the need to consider the exsolved oxide surface, in addition to the metal nanoparticles, in designing the exsolved nanocatalysts.\n
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\n \n\n \n \n \n \n \n Self-Assembled Multiphase Nanocomposite SrCo1–xFexO3-$δ$ Thin Films with Voltage-Controlled Magnetism for Spintronic Applications.\n \n \n \n\n\n \n Cho, E., Kumar, A., Ning, S., LeBeau, J. M, & Ross, C. A\n\n\n \n\n\n\n ACS Appl. Nano Mater., 5(10): 14646–14653. October 2022.\n \n\n\n\n
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@ARTICLE{Cho2022-xb,\n  title     = "{Self-Assembled} Multiphase Nanocomposite\n               {SrCo1--xFexO3-$\\delta$} Thin Films with {Voltage-Controlled}\n               Magnetism for Spintronic Applications",\n  author    = "Cho, Eunsoo and Kumar, Abinash and Ning, Shuai and LeBeau, James\n               M and Ross, Caroline A",\n  abstract  = "SrCo1--xFexO3-$\\delta$ (SCFO) grown on SrTiO3 substrates using\n               pulsed laser deposition forms either a single-phase film or a\n               two-phase self-assembled nanocomposite film depending on the\n               oxygen partial pressure, PO2. A high PO2 of 150 mTorr during\n               growth promotes phase separation of SCFO into a nanocomposite\n               comprising Co oxide pillars embedded epitaxially in a Fe-rich\n               SCFO matrix made up of brownmillerite and oxygen-deficient\n               perovskite, despite the average composition of Sr/(Co + Fe) = 1.\n               The SCFO matrix in the nanocomposite consists of a\n               brownmillerite structure at a high Co content and an oxygen\n               vacancy ordered perovskite at a high Fe content. In contrast,\n               single-phase SCFO films grow at 20 mTorr. Ionic liquid gating of\n               the nanocomposites oxidizes brownmillerite into perovskite with\n               interlayer defects and renders the matrix phase magnetic with a\n               saturation magnetization of 200 emu cm--3 at 173 K when x =\n               0.30.",\n  journal   = "ACS Appl. Nano Mater.",\n  publisher = "American Chemical Society",\n  volume    =  5,\n  number    =  10,\n  pages     = "14646--14653",\n  month     =  oct,\n  year      =  2022,\n  keywords  = "LeBeau Group;CHARM",\n  doi       = "10.1021/acsanm.2c03019"\n}\n\n
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\n SrCo1–xFexO3-$δ$ (SCFO) grown on SrTiO3 substrates using pulsed laser deposition forms either a single-phase film or a two-phase self-assembled nanocomposite film depending on the oxygen partial pressure, PO2. A high PO2 of 150 mTorr during growth promotes phase separation of SCFO into a nanocomposite comprising Co oxide pillars embedded epitaxially in a Fe-rich SCFO matrix made up of brownmillerite and oxygen-deficient perovskite, despite the average composition of Sr/(Co + Fe) = 1. The SCFO matrix in the nanocomposite consists of a brownmillerite structure at a high Co content and an oxygen vacancy ordered perovskite at a high Fe content. In contrast, single-phase SCFO films grow at 20 mTorr. Ionic liquid gating of the nanocomposites oxidizes brownmillerite into perovskite with interlayer defects and renders the matrix phase magnetic with a saturation magnetization of 200 emu cm–3 at 173 K when x = 0.30.\n
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\n \n\n \n \n \n \n \n Strong and Localized Luminescence from Interface Bubbles Between Stacked hBN Multilayers.\n \n \n \n\n\n \n Lee, H. Y., Sarkar, S., Reidy, K., Kumar, A., Klein, J., Watanabe, K., Taniguchi, T., LeBeau, J. M, Ross, F. M, & Grade ̌cak, S.\n\n\n \n\n\n\n Nat. Commun., 13(1): 5000. August 2022.\n \n\n\n\n
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@ARTICLE{Lee2022-pg,\n  title    = "Strong and Localized Luminescence from Interface Bubbles Between\n              Stacked {hBN} Multilayers",\n  author   = "Lee, Hae Yeon and Sarkar, Soumya and Reidy, Kate and Kumar,\n              Abinash and Klein, Julian and Watanabe, Kenji and Taniguchi,\n              Takashi and LeBeau, James M and Ross, Frances M and Grade{\\v\n              c}ak, Silvija",\n  abstract = "Extraordinary optoelectronic properties of van der Waals (vdW)\n              heterostructures can be tuned via strain caused by mechanical\n              deformation. Here, we demonstrate strong and localized\n              luminescence in the ultraviolet region from interface bubbles\n              between stacked multilayers of hexagonal boron nitride (hBN).\n              Compared to bubbles in stacked monolayers, bubbles formed by\n              stacking vdW multilayers show distinct mechanical behavior. We\n              use this behavior to elucidate radius- and thickness-dependent\n              bubble geometry and the resulting strain across the bubble, from\n              which we establish the thickness-dependent bending rigidity of\n              hBN multilayers. We then utilize the polymeric material confined\n              within the bubbles to modify the bubble geometry under electron\n              beam irradiation, resulting in strong luminescence and formation\n              of optical standing waves. Our results open a route to design and\n              modulate microscopic-scale optical cavities via strain\n              engineering in vdW materials, which we suggest will be relevant\n              to both fundamental mechanical studies and optoelectronic\n              applications.",\n  journal  = "Nat. Commun.",\n  volume   =  13,\n  number   =  1,\n  pages    = "5000",\n  month    =  aug,\n  year     =  2022,\n  keywords = "LeBeau Group",\n  language = "en",\n  issn     = "2041-1723",\n  pmid     = "36008409",\n  doi      = "10.1038/s41467-022-32708-z",\n  pmc      = "PMC9411575"\n}\n\n
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\n Extraordinary optoelectronic properties of van der Waals (vdW) heterostructures can be tuned via strain caused by mechanical deformation. Here, we demonstrate strong and localized luminescence in the ultraviolet region from interface bubbles between stacked multilayers of hexagonal boron nitride (hBN). Compared to bubbles in stacked monolayers, bubbles formed by stacking vdW multilayers show distinct mechanical behavior. We use this behavior to elucidate radius- and thickness-dependent bubble geometry and the resulting strain across the bubble, from which we establish the thickness-dependent bending rigidity of hBN multilayers. We then utilize the polymeric material confined within the bubbles to modify the bubble geometry under electron beam irradiation, resulting in strong luminescence and formation of optical standing waves. Our results open a route to design and modulate microscopic-scale optical cavities via strain engineering in vdW materials, which we suggest will be relevant to both fundamental mechanical studies and optoelectronic applications.\n
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\n \n\n \n \n \n \n \n Nanotwinning-assisted dynamic recrystallization at high strains and strain rates.\n \n \n \n\n\n \n Tiamiyu, A. A, Pang, E. L, Chen, X., LeBeau, J. M, Nelson, K. A, & Schuh, C. A\n\n\n \n\n\n\n Nat. Mater.,1–9. May 2022.\n \n\n\n\n
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@ARTICLE{Tiamiyu2022-le,\n  title     = "Nanotwinning-assisted dynamic recrystallization at high strains\n               and strain rates",\n  author    = "Tiamiyu, Ahmed A and Pang, Edward L and Chen, Xi and LeBeau,\n               James M and Nelson, Keith A and Schuh, Christopher A",\n  abstract  = "Grain refinement is a widely sought-after feature of many metal\n               production processes and frequently involves a process of\n               recrystallization. Some processing methods use very high strain\n               rates and high strains to refine the grain structure into the\n               nanocrystalline regime. However, grain refinement processes are\n               not clear in these extreme conditions, which are hard to study\n               systematically. Here, we access those extreme conditions of\n               strain and strain rate using single copper microparticle impact\n               events with a laser-induced particle impact tester. Using a\n               combined dictionary-indexing electron backscatter diffraction\n               and scanning transmission electron microscopy approach for\n               postmortem characterization of impact sites, we systematically\n               explore increasing strain levels and observe a recrystallization\n               process that is facilitated by nanotwinning, which we term\n               nanotwinning-assisted dynamic recrystallization. It achieves\n               much finer grain sizes than established modes of\n               recrystallization and therefore provides a pathway to the finest\n               nanocrystalline grain sizes through extreme straining processes.\n               Extreme mechanical deformation processes can lead to nanograins\n               in many metals, but the underlying mechanism remains unclear.\n               Nanotwinning-assisted dynamic recrystallization is shown to\n               facilitate grain refinement to the nanoscale at high strains and\n               strain rates.",\n  journal   = "Nat. Mater.",\n  publisher = "Nature Publishing Group",\n  pages     = "1--9",\n  month     =  may,\n  year      =  2022,\n  keywords  = "LeBeau Group;DMREF;PECASE;PECASE 2023-2024",\n  language  = "en",\n  issn      = "1476-1122",\n  doi       = "10.1038/s41563-022-01250-0"\n}\n\n
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\n Grain refinement is a widely sought-after feature of many metal production processes and frequently involves a process of recrystallization. Some processing methods use very high strain rates and high strains to refine the grain structure into the nanocrystalline regime. However, grain refinement processes are not clear in these extreme conditions, which are hard to study systematically. Here, we access those extreme conditions of strain and strain rate using single copper microparticle impact events with a laser-induced particle impact tester. Using a combined dictionary-indexing electron backscatter diffraction and scanning transmission electron microscopy approach for postmortem characterization of impact sites, we systematically explore increasing strain levels and observe a recrystallization process that is facilitated by nanotwinning, which we term nanotwinning-assisted dynamic recrystallization. It achieves much finer grain sizes than established modes of recrystallization and therefore provides a pathway to the finest nanocrystalline grain sizes through extreme straining processes. Extreme mechanical deformation processes can lead to nanograins in many metals, but the underlying mechanism remains unclear. Nanotwinning-assisted dynamic recrystallization is shown to facilitate grain refinement to the nanoscale at high strains and strain rates.\n
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\n \n\n \n \n \n \n \n Coupled polarization and nanodomain evolution underpins large electromechanical responses in relaxors.\n \n \n \n\n\n \n Kim, J., Kumar, A., Qi, Y., Takenaka, H., Ryan, P. J, Meyers, D., Kim, J., Fernandez, A., Tian, Z., Rappe, A. M, LeBeau, J. M, & Martin, L. W\n\n\n \n\n\n\n Nat. Phys., 18(12): 1502–1509. October 2022.\n \n\n\n\n
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@ARTICLE{Kim2022-hl,\n  title     = "Coupled polarization and nanodomain evolution underpins large\n               electromechanical responses in relaxors",\n  author    = "Kim, Jieun and Kumar, Abinash and Qi, Yubo and Takenaka,\n               Hiroyuki and Ryan, Philip J and Meyers, Derek and Kim, Jong-Woo\n               and Fernandez, Abel and Tian, Zishen and Rappe, Andrew M and\n               LeBeau, James M and Martin, Lane W",\n  abstract  = "Understanding the evolution and role of nanoscale polar\n               structures during polarization rotation in relaxor\n               ferroelectrics is a long-standing challenge in materials science\n               and condensed-matter physics. These nanoscale polar structures\n               are characterized by polar nanodomains, which are believed to\n               play a key role in enabling the large susceptibilities of\n               relaxors. Using epitaxial strain, we stabilize the intermediate\n               step during polarization rotation in epitaxial films of a\n               prototypical relaxor and study the co-evolution of polarization\n               and polar nanodomains. Our multimodal approach allows for a\n               detailed examination of correlations between polarization and\n               polar nanodomains; illuminates the effect of local chemistry,\n               strain and electric field on their co-evolution; and reveals the\n               underappreciated role of strain in enabling the large\n               electromechanical coupling in relaxors. As the strain increases,\n               the competition between chemistry-driven disorder and\n               strain-driven order of the polar units intensifies, which is\n               manifested in the coexistence of inclined and elongated polar\n               nanodomains in the intermediate step of polarization rotation.\n               Our findings establish that structural transitions between polar\n               nanodomain configurations underpins the polarization rotation\n               and large electromechanical coupling of relaxors. Properties of\n               relaxor ferroelectrics are governed by polar nanodomains.\n               Polarization rotation facilitated by these domains investigated\n               by means of epitaxial strain reveals a competition between\n               chemistry-driven disorder and strain-driven order.",\n  journal   = "Nat. Phys.",\n  publisher = "Nature Publishing Group",\n  volume    =  18,\n  number    =  12,\n  pages     = "1502--1509",\n  month     =  oct,\n  year      =  2022,\n  keywords  = "LeBeau Group;CHARM",\n  language  = "en",\n  issn      = "1745-2473",\n  doi       = "10.1038/s41567-022-01773-y"\n}\n\n
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\n Understanding the evolution and role of nanoscale polar structures during polarization rotation in relaxor ferroelectrics is a long-standing challenge in materials science and condensed-matter physics. These nanoscale polar structures are characterized by polar nanodomains, which are believed to play a key role in enabling the large susceptibilities of relaxors. Using epitaxial strain, we stabilize the intermediate step during polarization rotation in epitaxial films of a prototypical relaxor and study the co-evolution of polarization and polar nanodomains. Our multimodal approach allows for a detailed examination of correlations between polarization and polar nanodomains; illuminates the effect of local chemistry, strain and electric field on their co-evolution; and reveals the underappreciated role of strain in enabling the large electromechanical coupling in relaxors. As the strain increases, the competition between chemistry-driven disorder and strain-driven order of the polar units intensifies, which is manifested in the coexistence of inclined and elongated polar nanodomains in the intermediate step of polarization rotation. Our findings establish that structural transitions between polar nanodomain configurations underpins the polarization rotation and large electromechanical coupling of relaxors. Properties of relaxor ferroelectrics are governed by polar nanodomains. Polarization rotation facilitated by these domains investigated by means of epitaxial strain reveals a competition between chemistry-driven disorder and strain-driven order.\n
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\n \n\n \n \n \n \n \n Reactivation of chromia poisoned oxygen exchange kinetics in mixed conducting solid oxide fuel cell electrodes by serial infiltration of lithia.\n \n \n \n\n\n \n Seo, H. G., Staerz, A. F., Kim, D. S, Klotz, D., Nicollet, C., Xu, M., LeBeau, J. M, & Tuller, H. L\n\n\n \n\n\n\n Energy Environ. Sci.. August 2022.\n \n\n\n\n
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@ARTICLE{Seo2022-wg,\n  title     = "Reactivation of chromia poisoned oxygen exchange kinetics in\n               mixed conducting solid oxide fuel cell electrodes by serial\n               infiltration of lithia",\n  author    = "Seo, Han Gil and Staerz, Anna Friederike and Kim, Dennis S and\n               Klotz, Dino and Nicollet, Clement and Xu, Michael and LeBeau,\n               James M and Tuller, Harry L",\n  abstract  = "Solid oxide fuel cells have the potential to render the\n               conversion from fuel to electrical energy more efficienct while\n               lowering emissions. The technology, however, suffers from\n               performance degradation due to cathode poisoning by chromia from\n               metal interconnects. We confirm the deleterious impact of\n               chromia on the performance of the model mixed conducting cathode\n               material Pr0.1Ce0.9O2- by examining the oxygen exchange\n               coefficient (kchem) via electrical conductivity relaxation\n               measurements, and the area-specific resistance (ASR) by\n               electrochemical impedance spectroscopy. Liquid Cr-infiltration\n               decreases kchem 20-fold and the oxygen exchange component of ASR\n               increases 20-fold while maintaining the same activation energy.\n               We then demonstrate the ability to not only recover initial\n               kchem and ASR values, but improve properties above those\n               exhibited by the pristine specimen through subsequent\n               Li-infiltration, leading to enhancement of kchem by more than\n               three orders of magnitude and reduction in oxygen exchange\n               component of the ASR over by a factor 100. We attribute these\n               dramatic changes to the depletion of electrons induced by the\n               acidic Cr-infiltrant on the Pr0.1Ce0.9O2- surface and the\n               recovery to accumulation of electrons from the basic\n               Li-infiltrant. These results point to acidity as a key\n               descriptor in addressing the long-standing challenge of reactive\n               surface poisoning in applications reliant on rapid oxygen\n               exchange and recovery behavior. The ability to achieve\n               remarkable levels of recovery of electrocatalytic surfaces by\n               controlling the relative acidity of surface species is\n               demonstrated for the first time.",\n  journal   = "Energy Environ. Sci.",\n  publisher = "The Royal Society of Chemistry",\n  month     =  aug,\n  year      =  2022,\n  keywords  = "LeBeau Group;PECASE;PFIB;PECASE 2023-2024",\n  language  = "en",\n  issn      = "1754-5692, 1754-5706",\n  doi       = "10.1039/D1EE03975J"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Solid oxide fuel cells have the potential to render the conversion from fuel to electrical energy more efficienct while lowering emissions. The technology, however, suffers from performance degradation due to cathode poisoning by chromia from metal interconnects. We confirm the deleterious impact of chromia on the performance of the model mixed conducting cathode material Pr0.1Ce0.9O2- by examining the oxygen exchange coefficient (kchem) via electrical conductivity relaxation measurements, and the area-specific resistance (ASR) by electrochemical impedance spectroscopy. Liquid Cr-infiltration decreases kchem 20-fold and the oxygen exchange component of ASR increases 20-fold while maintaining the same activation energy. We then demonstrate the ability to not only recover initial kchem and ASR values, but improve properties above those exhibited by the pristine specimen through subsequent Li-infiltration, leading to enhancement of kchem by more than three orders of magnitude and reduction in oxygen exchange component of the ASR over by a factor 100. We attribute these dramatic changes to the depletion of electrons induced by the acidic Cr-infiltrant on the Pr0.1Ce0.9O2- surface and the recovery to accumulation of electrons from the basic Li-infiltrant. These results point to acidity as a key descriptor in addressing the long-standing challenge of reactive surface poisoning in applications reliant on rapid oxygen exchange and recovery behavior. The ability to achieve remarkable levels of recovery of electrocatalytic surfaces by controlling the relative acidity of surface species is demonstrated for the first time.\n
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\n \n\n \n \n \n \n \n Thickness and temperature dependence of the atomic-scale structure of SrRuO$_{3}$ thin films.\n \n \n \n\n\n \n Zhang, X., Penn, A. N, Wysocki, L., Zhang, Z., van Loosdrecht, P. H M, Kornblum, L., LeBeau, J. M, Lindfors-Vrejoiu, I., & Kumah, D. P\n\n\n \n\n\n\n APL Materials, 10(5): 051107. May 2022.\n \n\n\n\n
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@ARTICLE{Zhang2022-ay,\n  title     = "Thickness and temperature dependence of the atomic-scale\n               structure of {SrRuO$_{3}$} thin films",\n  author    = "Zhang, Xuanyi and Penn, Aubrey N and Wysocki, Lena and Zhang,\n               Zhan and van Loosdrecht, Paul H M and Kornblum, Lior and LeBeau,\n               James M and Lindfors-Vrejoiu, Ionela and Kumah, Divine P",\n  abstract  = "The temperature-dependent layer-resolved structure of 3 to 44\n               unit cell thick SrRuO3 (SRO) films grown on Nb-doped SrTiO3\n               substrates is investigated using a combination of\n               high-resolution synchrotron x-ray diffraction and\n               high-resolution electron microscopy to understand the role that\n               structural distortions play in suppressing ferromagnetism in\n               ultra-thin SRO films. The oxygen octahedral tilts and rotations\n               and Sr displacements characteristic of the bulk orthorhombic\n               phase are found to be strongly dependent on temperature, the\n               film thickness, and the distance away from the film?substrate\n               interface. For thicknesses, t, above the critical thickness for\n               ferromagnetism (t > 3 uc), the orthorhombic distortions decrease\n               with increasing temperature above TC. Below TC, the structure of\n               the films remains constant due to the magneto-structural\n               coupling observed in bulk SRO. The orthorhombic distortions are\n               found to be suppressed in the 2?3 interfacial layers due to\n               structural coupling with the SrTiO3 substrate and correlate with\n               the critical thickness for ferromagnetism in uncapped SRO films.",\n  journal   = "APL Materials",\n  publisher = "American Institute of Physics",\n  volume    =  10,\n  number    =  5,\n  pages     = "051107",\n  month     =  may,\n  year      =  2022,\n  keywords  = "LeBeau Group",\n  doi       = "10.1063/5.0087791"\n}\n\n
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\n The temperature-dependent layer-resolved structure of 3 to 44 unit cell thick SrRuO3 (SRO) films grown on Nb-doped SrTiO3 substrates is investigated using a combination of high-resolution synchrotron x-ray diffraction and high-resolution electron microscopy to understand the role that structural distortions play in suppressing ferromagnetism in ultra-thin SRO films. The oxygen octahedral tilts and rotations and Sr displacements characteristic of the bulk orthorhombic phase are found to be strongly dependent on temperature, the film thickness, and the distance away from the film?substrate interface. For thicknesses, t, above the critical thickness for ferromagnetism (t > 3 uc), the orthorhombic distortions decrease with increasing temperature above TC. Below TC, the structure of the films remains constant due to the magneto-structural coupling observed in bulk SRO. The orthorhombic distortions are found to be suppressed in the 2?3 interfacial layers due to structural coupling with the SrTiO3 substrate and correlate with the critical thickness for ferromagnetism in uncapped SRO films.\n
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\n \n\n \n \n \n \n \n Accounting for Location Measurement Error in Imaging Data With Application to Atomic Resolution Images of Crystalline Materials.\n \n \n \n\n\n \n Miller, M. J, Cabral, M. J, Dickey, E. C, LeBeau, J. M, & Reich, B. J\n\n\n \n\n\n\n Technometrics, 64(1): 103–113. January 2022.\n \n\n\n\n
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@ARTICLE{Miller2022-qm,\n  title     = "Accounting for Location Measurement Error in Imaging Data With\n               Application to Atomic Resolution Images of Crystalline Materials",\n  author    = "Miller, Matthew J and Cabral, Matthew J and Dickey, Elizabeth C\n               and LeBeau, James M and Reich, Brian J",\n  abstract  = "AbstractScientists use imaging to identify objects of interest\n               and infer properties of these objects. The locations of these\n               objects are often measured with error, which when ignored leads\n               to biased parameter estimates and inflated variance. Current\n               measurement error methods require an estimate or knowledge of\n               the measurement error variance to correct these estimates, which\n               may not be available. Instead, we create a spatial Bayesian\n               hierarchical model that treats the locations as parameters,\n               using the image itself to incorporate positional uncertainty. We\n               lower the computational burden by approximating the likelihood\n               using a noncontiguous block design around the object locations.\n               We use this model to quantify the relationship between the\n               intensity and displacement of hundreds of atom columns in\n               crystal structures directly imaged via scanning transmission\n               electron microscopy (STEM). Atomic displacements are related to\n               important phenomena such as piezoelectricity, a property useful\n               for engineering applications like ultrasound. Quantifying the\n               sign and magnitude of this relationship will help materials\n               scientists more precisely design materials with improved\n               piezoelectricity. A simulation study confirms our method\n               corrects bias in the estimate of the parameter of interest and\n               drastically improves coverage in high noise scenarios compared\n               to non-measurement error models.",\n  journal   = "Technometrics",\n  publisher = "Taylor \\& Francis",\n  volume    =  64,\n  number    =  1,\n  pages     = "103--113",\n  month     =  jan,\n  year      =  2022,\n  keywords  = "LeBeau Group",\n  issn      = "0040-1706",\n  doi       = "10.1080/00401706.2021.1905070"\n}\n\n
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\n AbstractScientists use imaging to identify objects of interest and infer properties of these objects. The locations of these objects are often measured with error, which when ignored leads to biased parameter estimates and inflated variance. Current measurement error methods require an estimate or knowledge of the measurement error variance to correct these estimates, which may not be available. Instead, we create a spatial Bayesian hierarchical model that treats the locations as parameters, using the image itself to incorporate positional uncertainty. We lower the computational burden by approximating the likelihood using a noncontiguous block design around the object locations. We use this model to quantify the relationship between the intensity and displacement of hundreds of atom columns in crystal structures directly imaged via scanning transmission electron microscopy (STEM). Atomic displacements are related to important phenomena such as piezoelectricity, a property useful for engineering applications like ultrasound. Quantifying the sign and magnitude of this relationship will help materials scientists more precisely design materials with improved piezoelectricity. A simulation study confirms our method corrects bias in the estimate of the parameter of interest and drastically improves coverage in high noise scenarios compared to non-measurement error models.\n
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\n \n\n \n \n \n \n \n Rare earth based solid-state qubit platforms.\n \n \n \n\n\n \n Singh, M K, Ahn, J, Sullivan, S E, Kumar, A, Zhou, T, Ji, C, Grant, G, Sautter, K, Holt, M V, Dibos, A M, Heremans, F J, LeBeau, J M, Awschalom, D D, & Guha, S\n\n\n \n\n\n\n In 2022 International Electron Devices Meeting (IEDM), pages 14.2.1–14.2.4, December 2022. IEEE\n \n\n\n\n
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@INPROCEEDINGS{Singh2022-iv,\n  title           = "Rare earth based solid-state qubit platforms",\n  booktitle       = "2022 International Electron Devices Meeting ({IEDM})",\n  author          = "Singh, M K and Ahn, J and Sullivan, S E and Kumar, A and\n                     Zhou, T and Ji, C and Grant, G and Sautter, K and Holt, M\n                     V and Dibos, A M and Heremans, F J and LeBeau, J M and\n                     Awschalom, D D and Guha, S",\n  abstract        = "Rare earth ions (REIs) have emerged as a promising\n                     platform for quantum technology, especially as memories --\n                     given their long optical and spin coherence times. Along\n                     with a brief review of progress in the field, we show that\n                     doped thin films on silicon can be engineered to approach\n                     the properties shown in bulk REI doped crystals and can\n                     leverage CMOS nanofabrication methods for the development\n                     of integrated quantum devices.",\n  publisher       = "IEEE",\n  pages           = "14.2.1--14.2.4",\n  month           =  dec,\n  year            =  2022,\n  keywords        = "Particle beam\n                     optics;Nanofabrication;Qubit;Crystals;Ions;Silicon;Coherence\n                     time;LeBeau Group",\n  conference      = "2022 IEEE International Electron Devices Meeting (IEDM)",\n  location        = "San Francisco, CA, USA",\n  issn            = "2156-017X",\n  doi             = "10.1109/iedm45625.2022.10019546"\n}\n\n
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\n Rare earth ions (REIs) have emerged as a promising platform for quantum technology, especially as memories – given their long optical and spin coherence times. Along with a brief review of progress in the field, we show that doped thin films on silicon can be engineered to approach the properties shown in bulk REI doped crystals and can leverage CMOS nanofabrication methods for the development of integrated quantum devices.\n
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\n \n\n \n \n \n \n \n The Influence of Cr-Additives on the Polarization Resistance of Praseodymium-Doped Ceria Cathodes for Solid Oxide Fuel Cells.\n \n \n \n\n\n \n Staerz, A., Seo, H. G., Klotz, D., Kim, D. S, LeBeau, J. M, & Tuller, H. L\n\n\n \n\n\n\n J. Electrochem. Soc., 169(4): 044530. April 2022.\n \n\n\n\n
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@ARTICLE{Staerz2022-vg,\n  title     = "The Influence of {Cr-Additives} on the Polarization Resistance\n               of {Praseodymium-Doped} Ceria Cathodes for Solid Oxide Fuel\n               Cells",\n  author    = "Staerz, Anna and Seo, Han Gil and Klotz, Dino and Kim, Dennis S\n               and LeBeau, James M and Tuller, Harry L",\n  abstract  = "While Cr poisoning of the oxygen reduction reaction (ORR) at\n               SOFC cathodes is widely agreed to involve deactivation of oxygen\n               exchange sites, the degradation mechanism remains ambiguous.\n               Here, we selected an alternative cathode material Pr0.1Ce0.9O2−\n               free of Sr segregation, to systematically investigate the effect\n               of Cr-induced degradation in ORR. We expand on our previous\n               studies in which the acidity/basicity of binary additives was\n               found to be a strong indicator of the rate of oxygen surface\n               exchange, by electrochemically investigating the ORR activity of\n               the PCO cathode by impedance spectroscopy. Serial infiltration\n               with acidic Cr-based oxides was found to degrade ORR activity as\n               reflected in a 20-fold increase in area specific resistance\n               (ASR) without corresponding changes in activation energy, with\n               the opposite trend obtained with Ca-based oxides. Detected\n               changes in total capacitance, attributed to changes in surface\n               capacitance, also suggest depressed/enhanced PCO surface redox\n               behavior with Cr/Ca-based infiltrants. Taken together, these\n               results point to a more universal source of ORR\n               poisoning/activation, based on acidity/basicity, rather than\n               physical blocking of active sites. With this improved\n               understanding, one can expect progress to be made in the coming\n               years in optimizing means for protecting catalytic surfaces from\n               degradation and/or improving their performance.",\n  journal   = "J. Electrochem. Soc.",\n  publisher = "IOP Publishing",\n  volume    =  169,\n  number    =  4,\n  pages     = "044530",\n  month     =  apr,\n  year      =  2022,\n  keywords  = "LeBeau Group;DHS proposal;PFIB",\n  language  = "en",\n  issn      = "0013-4651",\n  doi       = "10.1149/1945-7111/ac67b2"\n}\n\n
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\n While Cr poisoning of the oxygen reduction reaction (ORR) at SOFC cathodes is widely agreed to involve deactivation of oxygen exchange sites, the degradation mechanism remains ambiguous. Here, we selected an alternative cathode material Pr0.1Ce0.9O2− free of Sr segregation, to systematically investigate the effect of Cr-induced degradation in ORR. We expand on our previous studies in which the acidity/basicity of binary additives was found to be a strong indicator of the rate of oxygen surface exchange, by electrochemically investigating the ORR activity of the PCO cathode by impedance spectroscopy. Serial infiltration with acidic Cr-based oxides was found to degrade ORR activity as reflected in a 20-fold increase in area specific resistance (ASR) without corresponding changes in activation energy, with the opposite trend obtained with Ca-based oxides. Detected changes in total capacitance, attributed to changes in surface capacitance, also suggest depressed/enhanced PCO surface redox behavior with Cr/Ca-based infiltrants. Taken together, these results point to a more universal source of ORR poisoning/activation, based on acidity/basicity, rather than physical blocking of active sites. With this improved understanding, one can expect progress to be made in the coming years in optimizing means for protecting catalytic surfaces from degradation and/or improving their performance.\n
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\n \n\n \n \n \n \n \n Red Bean Pod Derived Heterostructure Carbon Decorated with Hollow Mixed Transition Metals as a Bifunctional Catalyst in Zn-Air Batteries.\n \n \n \n\n\n \n Mahbub, M. A. A., Adios, C. G., Xu, M., Prakoso, B., LeBeau, J. M, & Sumboja, A.\n\n\n \n\n\n\n Chemistry - An Asian Journal, 16(17): 2559–2567. September 2021.\n \n\n\n\n
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@ARTICLE{Mahbub2021-ph,\n  title     = "Red Bean Pod Derived Heterostructure Carbon Decorated with\n               Hollow Mixed Transition Metals as a Bifunctional Catalyst in\n               {Zn-Air} Batteries",\n  author    = "Mahbub, Muhammad Adib Abdillah and Adios, Celfi Gustine and Xu,\n               Michael and Prakoso, Bagas and LeBeau, James M and Sumboja,\n               Afriyanti",\n  abstract  = "Design and synthesis of low-cost and efficient bifunctional\n               catalysts for oxygen reduction reaction (ORR) and oxygen\n               evolution reaction (OER) in Zn-air batteries are essential and\n               challenging. We report a facile method to synthesize\n               heterostructure carbon consisting of graphitic and amorphous\n               carbon derived from the agricultural waste of red bean pods. The\n               heterostructure carbon possesses a large surface area of 625.5\n               m2 g−1, showing ORR onset potential of 0.89 V vs. RHE and OER\n               overpotential of 470 mV at 5 mA cm−2. Introducing hollow FeCo\n               nanoparticles and nitrogen dopant improves the bifunctional\n               catalytic activity of the carbon, delivering ORR onset potential\n               of 0.93 V vs. RHE and OER overpotential of 360 mV. Electron\n               energy-loss spectroscopy (EELS) O K-edge map suggests the\n               presence of localized oxygen on the FeCo nanoparticles,\n               suggesting the oxidation of the nanoparticles. Zn-air battery\n               with these carbon-based catalysts exhibits a peak power density\n               as high as 116.2 mW cm−2 and stable cycling performance over 210\n               discharge/charge cycles. This work contributes to the\n               advancement of bifunctional oxygen electrocatalysts while\n               converting agricultural waste into value-added material.",\n  journal   = "Chemistry - An Asian Journal",\n  publisher = "John Wiley and Sons Ltd",\n  volume    =  16,\n  number    =  17,\n  pages     = "2559--2567",\n  month     =  sep,\n  year      =  2021,\n  keywords  = "Biomass-derived carbon; FeCo; electrocatalysis; metal-air\n               batteries; non-precious metal catalyst;LeBeau Group",\n  issn      = "1861-471X",\n  pmid      = "34382330",\n  doi       = "10.1002/ASIA.202100702"\n}\n\n
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\n Design and synthesis of low-cost and efficient bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Zn-air batteries are essential and challenging. We report a facile method to synthesize heterostructure carbon consisting of graphitic and amorphous carbon derived from the agricultural waste of red bean pods. The heterostructure carbon possesses a large surface area of 625.5 m2 g−1, showing ORR onset potential of 0.89 V vs. RHE and OER overpotential of 470 mV at 5 mA cm−2. Introducing hollow FeCo nanoparticles and nitrogen dopant improves the bifunctional catalytic activity of the carbon, delivering ORR onset potential of 0.93 V vs. RHE and OER overpotential of 360 mV. Electron energy-loss spectroscopy (EELS) O K-edge map suggests the presence of localized oxygen on the FeCo nanoparticles, suggesting the oxidation of the nanoparticles. Zn-air battery with these carbon-based catalysts exhibits a peak power density as high as 116.2 mW cm−2 and stable cycling performance over 210 discharge/charge cycles. This work contributes to the advancement of bifunctional oxygen electrocatalysts while converting agricultural waste into value-added material.\n
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\n \n\n \n \n \n \n \n Making BaZrS$_{3}$ Chalcogenide Perovskite Thin Films by Molecular Beam Epitaxy.\n \n \n \n\n\n \n Sadeghi, I., Ye, K., Xu, M., Li, Y., LeBeau, J. M, & Jaramillo, R.\n\n\n \n\n\n\n Adv. Funct. Mater., 31(45): 2105563. November 2021.\n \n\n\n\n
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@ARTICLE{Sadeghi2021-bf,\n  title    = "Making {BaZrS$_{3}$} Chalcogenide Perovskite Thin Films by\n              Molecular Beam Epitaxy",\n  author   = "Sadeghi, Ida and Ye, Kevin and Xu, Michael and Li, Yifei and\n              LeBeau, James M and Jaramillo, Rafael",\n  abstract = "We demonstrate the making of BaZrS3 thin films by molecular beam\n              epitaxy (MBE). BaZrS3 forms in the orthorhombic\n              distorted-perovskite structure with corner-sharing ZrS6\n              octahedra. The single-step MBE process results in films smooth on\n              the atomic scale, with near-perfect BaZrS3 stoichiometry and an\n              atomically-sharp interface with the LaAlO3 substrate. The films\n              grow epitaxially via two, competing growth modes: buffered\n              epitaxy, with a self-assembled interface layer that relieves the\n              epitaxial strain, and direct epitaxy, with rotated-cube-on-cube\n              growth that accommodates the large lattice constant mismatch\n              between the oxide and the sulfide perovskites. This work sets the\n              stage for developing chalcogenide perovskites as a family of\n              semiconductor alloys with properties that can be tuned with\n              strain and composition in high-quality epitaxial thin films, as\n              has been long-established for other systems including Si-Ge,\n              III-Vs, and II-Vs. The methods demonstrated here also represent a\n              revival of gas-source chalcogenide MBE.",\n  journal  = "Adv. Funct. Mater.",\n  volume   =  31,\n  number   =  45,\n  pages    = "2105563",\n  month    =  nov,\n  year     =  2021,\n  keywords = "LeBeau Group;AFOSR;PECASE;PECASE 2023-2024",\n  issn     = "1616-301X",\n  doi      = "10.1002/adfm.202105563"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n We demonstrate the making of BaZrS3 thin films by molecular beam epitaxy (MBE). BaZrS3 forms in the orthorhombic distorted-perovskite structure with corner-sharing ZrS6 octahedra. The single-step MBE process results in films smooth on the atomic scale, with near-perfect BaZrS3 stoichiometry and an atomically-sharp interface with the LaAlO3 substrate. The films grow epitaxially via two, competing growth modes: buffered epitaxy, with a self-assembled interface layer that relieves the epitaxial strain, and direct epitaxy, with rotated-cube-on-cube growth that accommodates the large lattice constant mismatch between the oxide and the sulfide perovskites. This work sets the stage for developing chalcogenide perovskites as a family of semiconductor alloys with properties that can be tuned with strain and composition in high-quality epitaxial thin films, as has been long-established for other systems including Si-Ge, III-Vs, and II-Vs. The methods demonstrated here also represent a revival of gas-source chalcogenide MBE.\n
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\n \n\n \n \n \n \n \n Entropy Landscaping of High-Entropy Carbides.\n \n \n \n\n\n \n Hossain, M. D., Borman, T., Oses, C., Esters, M., Toher, C., Feng, L., Kumar, A., Fahrenholtz, W. G, Curtarolo, S., Brenner, D., LeBeau, J. M, & Maria, J.\n\n\n \n\n\n\n Adv. Mater., 33(42): 2102904. October 2021.\n \n\n\n\n
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@ARTICLE{Hossain2021-ig,\n  title    = "Entropy Landscaping of {High-Entropy} Carbides",\n  author   = "Hossain, Mohammad Delower and Borman, Trent and Oses, Corey and\n              Esters, Marco and Toher, Cormac and Feng, Lun and Kumar, Abinash\n              and Fahrenholtz, William G and Curtarolo, Stefano and Brenner,\n              Donald and LeBeau, James M and Maria, Jon‐paul",\n  journal  = "Adv. Mater.",\n  volume   =  33,\n  number   =  42,\n  pages    = "2102904",\n  month    =  oct,\n  year     =  2021,\n  keywords = "LeBeau Group;PECASE 2023-2024",\n  issn     = "0935-9648",\n  doi      = "10.1002/adma.202102904"\n}\n\n
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\n \n\n \n \n \n \n \n Carbon stoichiometry and mechanical properties of high entropy carbides.\n \n \n \n\n\n \n Hossain, M D, Borman, T, Kumar, A, Chen, X, Khosravani, A, Kalidindi, S R, Paisley, E A, Esters, M, Oses, C, Toher, C, Curtarolo, S, LeBeau, J M, Brenner, D, & Maria, J.\n\n\n \n\n\n\n Acta Mater., 215: 117051. August 2021.\n \n\n\n\n
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@ARTICLE{Hossain2021-da,\n  title    = "Carbon stoichiometry and mechanical properties of high entropy\n              carbides",\n  author   = "Hossain, M D and Borman, T and Kumar, A and Chen, X and\n              Khosravani, A and Kalidindi, S R and Paisley, E A and Esters, M\n              and Oses, C and Toher, C and Curtarolo, S and LeBeau, J M and\n              Brenner, D and Maria, J-P",\n  journal  = "Acta Mater.",\n  volume   =  215,\n  pages    = "117051",\n  month    =  aug,\n  year     =  2021,\n  keywords = "LeBeau Group",\n  issn     = "1359-6454",\n  doi      = "10.1016/j.actamat.2021.117051"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n \n\n \n \n \n \n \n Efficient self-powered wearable electronic systems enabled by microwave processed thermoelectric materials.\n \n \n \n\n\n \n Nozariasbmarz, A., Dycus, J H., Cabral, M. J, Flack, C. M, Krasinski, J. S, LeBeau, J. M, & Vashaee, D.\n\n\n \n\n\n\n Appl. Energy, 283: 116211. February 2021.\n \n\n\n\n
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@ARTICLE{Nozariasbmarz2021-ip,\n  title    = "Efficient self-powered wearable electronic systems enabled by\n              microwave processed thermoelectric materials",\n  author   = "Nozariasbmarz, Amin and Dycus, J Houston and Cabral, Matthew J\n              and Flack, Chloe M and Krasinski, Jerzy S and LeBeau, James M and\n              Vashaee, Daryoosh",\n  journal  = "Appl. Energy",\n  volume   =  283,\n  pages    = "116211",\n  month    =  feb,\n  year     =  2021,\n  keywords = "LeBeau Group",\n  issn     = "0306-2619",\n  doi      = "10.1016/j.apenergy.2020.116211"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n \n\n \n \n \n \n \n Frequency-dependent suppression of field-induced polarization rotation in relaxor ferroelectric thin films.\n \n \n \n\n\n \n Kim, J., Meyers, D. J, Kumar, A., Fernandez, A., Velarde, G. A P, Tian, Z., Kim, J., LeBeau, J. M, Ryan, P. J, & Martin, L. W\n\n\n \n\n\n\n Matter, 4(7): 2367–2377. July 2021.\n \n\n\n\n
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@ARTICLE{Kim2021-jo,\n  title    = "Frequency-dependent suppression of field-induced polarization\n              rotation in relaxor ferroelectric thin films",\n  author   = "Kim, Jieun and Meyers, Derek J and Kumar, Abinash and Fernandez,\n              Abel and Velarde, Gabriel A P and Tian, Zishen and Kim, Jong-Woo\n              and LeBeau, James M and Ryan, Philip J and Martin, Lane W",\n  abstract = "Summary The dynamics of polarization evolution and rotation in\n              0.68PbMg1/3Nb2/3O3-0.32PbTiO3 relaxor ferroelectric thin films\n              are studied via in operando synchrotron-based X-ray diffraction\n              with AC electric fields. A frequency-limited suppression of\n              polarization rotation was observed above ultrasonic frequencies\n              (≳ 20 kHz). The nature of this suppression is informed by\n              scanning transmission electron microscopy in the zero-field\n              state, where a high density of nanoscale, low-angle domain walls\n              was observed. In combination with switching dynamics studies, the\n              results suggest that the suppression of polarization rotation at\n              ultrasonic frequencies is due to the large activation field\n              needed to move the domain walls when the polarization rotates\n              between different monoclinic phases. These results are critical\n              in understanding piezoelectric relaxation phenomena in relaxor\n              ferroelectrics.",\n  journal  = "Matter",\n  volume   =  4,\n  number   =  7,\n  pages    = "2367--2377",\n  month    =  jul,\n  year     =  2021,\n  keywords = "relaxor ferroelectrics; X-ray diffraction; nanodomains; scanning\n              transmission electron microscopy; polarization rotation;LeBeau\n              Group",\n  issn     = "2590-2385",\n  doi      = "10.1016/j.matt.2021.04.017"\n}\n\n
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\n Summary The dynamics of polarization evolution and rotation in 0.68PbMg1/3Nb2/3O3-0.32PbTiO3 relaxor ferroelectric thin films are studied via in operando synchrotron-based X-ray diffraction with AC electric fields. A frequency-limited suppression of polarization rotation was observed above ultrasonic frequencies (≳ 20 kHz). The nature of this suppression is informed by scanning transmission electron microscopy in the zero-field state, where a high density of nanoscale, low-angle domain walls was observed. In combination with switching dynamics studies, the results suggest that the suppression of polarization rotation at ultrasonic frequencies is due to the large activation field needed to move the domain walls when the polarization rotates between different monoclinic phases. These results are critical in understanding piezoelectric relaxation phenomena in relaxor ferroelectrics.\n
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\n \n\n \n \n \n \n \n Direct imaging and electronic structure modulation of moiré superlattices at the 2D/3D interface.\n \n \n \n\n\n \n Reidy, K., Varnavides, G., Thomsen, J. D., Kumar, A., Pham, T., Blackburn, A. M, Anikeeva, P., Narang, P., LeBeau, J. M, & Ross, F. M\n\n\n \n\n\n\n Nat. Commun., 12(1): 1290. February 2021.\n \n\n\n\n
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@ARTICLE{Reidy2021-ff,\n  title     = "Direct imaging and electronic structure modulation of moir{\\'e}\n               superlattices at the {2D/3D} interface",\n  author    = "Reidy, Kate and Varnavides, Georgios and Thomsen, Joachim Dahl\n               and Kumar, Abinash and Pham, Thang and Blackburn, Arthur M and\n               Anikeeva, Polina and Narang, Prineha and LeBeau, James M and\n               Ross, Frances M",\n  abstract  = "The atomic structure at the interface between two-dimensional\n               (2D) and three-dimensional (3D) materials influences properties\n               such as contact resistance, photo-response, and high-frequency\n               electrical performance. Moir{\\'e} engineering is yet to be\n               utilized for tailoring this 2D/3D interface, despite its success\n               in enabling correlated physics at 2D/2D interfaces. Using\n               epitaxially aligned MoS2/Au\\{111\\} as a model system, we\n               demonstrate the use of advanced scanning transmission electron\n               microscopy (STEM) combined with a geometric convolution\n               technique in imaging the crystallographic 32 {\\AA} moir{\\'e}\n               pattern at the 2D/3D interface. This moir{\\'e} period is often\n               hidden in conventional electron microscopy, where the Au\n               structure is seen in projection. We show, via ab initio\n               electronic structure calculations, that charge density is\n               modulated according to the moir{\\'e} period, illustrating the\n               potential for (opto-)electronic moir{\\'e} engineering at the\n               2D/3D interface. Our work presents a general pathway to directly\n               image periodic modulation at interfaces using this combination\n               of emerging microscopy techniques.",\n  journal   = "Nat. Commun.",\n  publisher = "Springer US",\n  volume    =  12,\n  number    =  1,\n  pages     = "1290",\n  month     =  feb,\n  year      =  2021,\n  keywords  = "LeBeau Group",\n  language  = "en",\n  issn      = "2041-1723",\n  pmid      = "33637704",\n  doi       = "10.1038/s41467-021-21363-5",\n  pmc       = "PMC7910301"\n}\n\n
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\n The atomic structure at the interface between two-dimensional (2D) and three-dimensional (3D) materials influences properties such as contact resistance, photo-response, and high-frequency electrical performance. Moiré engineering is yet to be utilized for tailoring this 2D/3D interface, despite its success in enabling correlated physics at 2D/2D interfaces. Using epitaxially aligned MoS2/Au\\111\\ as a model system, we demonstrate the use of advanced scanning transmission electron microscopy (STEM) combined with a geometric convolution technique in imaging the crystallographic 32 Å moiré pattern at the 2D/3D interface. This moiré period is often hidden in conventional electron microscopy, where the Au structure is seen in projection. We show, via ab initio electronic structure calculations, that charge density is modulated according to the moiré period, illustrating the potential for (opto-)electronic moiré engineering at the 2D/3D interface. Our work presents a general pathway to directly image periodic modulation at interfaces using this combination of emerging microscopy techniques.\n
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\n \n\n \n \n \n \n \n An antisite defect mechanism for room temperature ferroelectricity in orthoferrites.\n \n \n \n\n\n \n Ning, S., Kumar, A., Klyukin, K., Cho, E., Kim, J. H., Su, T., Kim, H., LeBeau, J. M, Yildiz, B., & Ross, C. A\n\n\n \n\n\n\n Nat. Commun., 12(1): 4298. July 2021.\n \n\n\n\n
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@ARTICLE{Ning2021-to,\n  title    = "An antisite defect mechanism for room temperature\n              ferroelectricity in orthoferrites",\n  author   = "Ning, Shuai and Kumar, Abinash and Klyukin, Konstantin and Cho,\n              Eunsoo and Kim, Jong Heon and Su, Tingyu and Kim, Hyun-Suk and\n              LeBeau, James M and Yildiz, Bilge and Ross, Caroline A",\n  abstract = "Single-phase multiferroic materials that allow the coexistence of\n              ferroelectric and magnetic ordering above room temperature are\n              highly desirable, motivating an ongoing search for mechanisms for\n              unconventional ferroelectricity in magnetic oxides. Here, we\n              report an antisite defect mechanism for room temperature\n              ferroelectricity in epitaxial thin films of yttrium orthoferrite,\n              YFeO3, a perovskite-structured canted antiferromagnet. A\n              combination of piezoresponse force microscopy, atomically\n              resolved elemental mapping with aberration corrected scanning\n              transmission electron microscopy and density functional theory\n              calculations reveals that the presence of YFe antisite defects\n              facilitates a non-centrosymmetric distortion promoting\n              ferroelectricity. This mechanism is predicted to work analogously\n              for other rare earth orthoferrites, with a dependence of the\n              polarization on the radius of the rare earth cation. Our work\n              uncovers the distinctive role of antisite defects in providing a\n              mechanism for ferroelectricity in a range of magnetic\n              orthoferrites and further augments the functionality of this\n              family of complex oxides for multiferroic applications.",\n  journal  = "Nat. Commun.",\n  volume   =  12,\n  number   =  1,\n  pages    = "4298",\n  month    =  jul,\n  year     =  2021,\n  keywords = "PFIB;LeBeau Group",\n  language = "en",\n  issn     = "2041-1723",\n  pmid     = "34262033",\n  doi      = "10.1038/s41467-021-24592-w",\n  pmc      = "PMC8280199"\n}\n\n
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\n Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO3, a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of YFe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Our work uncovers the distinctive role of antisite defects in providing a mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications.\n
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\n \n\n \n \n \n \n \n Atomic-resolution electron microscopy of nanoscale local structure in lead-based relaxor ferroelectrics.\n \n \n \n\n\n \n Kumar, A., Baker, J. N, Bowes, P. C, Cabral, M. J, Zhang, S., Dickey, E. C, Irving, D. L, & LeBeau, J. M\n\n\n \n\n\n\n Nat. Mater., 20(1): 62–67. January 2021.\n \n\n\n\n
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@ARTICLE{Kumar2021-xk,\n  title     = "Atomic-resolution electron microscopy of nanoscale local\n               structure in lead-based relaxor ferroelectrics",\n  author    = "Kumar, Abinash and Baker, Jonathon N and Bowes, Preston C and\n               Cabral, Matthew J and Zhang, Shujun and Dickey, Elizabeth C and\n               Irving, Douglas L and LeBeau, James M",\n  abstract  = "Relaxor ferroelectrics, which can exhibit exceptional\n               electromechanical coupling, are some of the most important\n               functional materials, with applications ranging from ultrasound\n               imaging to actuators. Since their discovery, their complex\n               nanoscale chemical and structural heterogeneity has made the\n               origins of their electromechanical properties extremely\n               difficult to understand. Here, we employ aberration-corrected\n               scanning transmission electron microscopy to quantify various\n               types of nanoscale heterogeneities and their connection to local\n               polarization in the prototypical relaxor ferroelectric system\n               Pb(Mg1/3Nb2/3)O3-PbTiO3. We identify three main contributions\n               that each depend on Ti content: chemical order, oxygen\n               octahedral tilt and oxygen octahedral distortion. These\n               heterogeneities are found to be spatially correlated with\n               low-angle polar domain walls, indicating their role in\n               disrupting long-range polarization and leading to nanoscale\n               domain formation and the relaxor response. We further locate\n               nanoscale regions of monoclinic-like distortion that correlate\n               directly with Ti content and electromechanical performance.\n               Through this approach, the connections between chemical\n               heterogeneity, structural heterogeneity and local polarization\n               are revealed, validating models that are needed to develop the\n               next generation of relaxor ferroelectrics.",\n  journal   = "Nat. Mater.",\n  publisher = "Nature Research",\n  volume    =  20,\n  number    =  1,\n  pages     = "62--67",\n  month     =  jan,\n  year      =  2021,\n  keywords  = "Engineering; Ferroelectrics and multiferroics; Materials\n               science;LeBeau Group;AFOSR;DHS proposal;Amazon",\n  language  = "en",\n  issn      = "1476-1122, 1476-4660",\n  pmid      = "32895506",\n  doi       = "10.1038/s41563-020-0794-5"\n}\n\n
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\n Relaxor ferroelectrics, which can exhibit exceptional electromechanical coupling, are some of the most important functional materials, with applications ranging from ultrasound imaging to actuators. Since their discovery, their complex nanoscale chemical and structural heterogeneity has made the origins of their electromechanical properties extremely difficult to understand. Here, we employ aberration-corrected scanning transmission electron microscopy to quantify various types of nanoscale heterogeneities and their connection to local polarization in the prototypical relaxor ferroelectric system Pb(Mg1/3Nb2/3)O3-PbTiO3. We identify three main contributions that each depend on Ti content: chemical order, oxygen octahedral tilt and oxygen octahedral distortion. These heterogeneities are found to be spatially correlated with low-angle polar domain walls, indicating their role in disrupting long-range polarization and leading to nanoscale domain formation and the relaxor response. We further locate nanoscale regions of monoclinic-like distortion that correlate directly with Ti content and electromechanical performance. Through this approach, the connections between chemical heterogeneity, structural heterogeneity and local polarization are revealed, validating models that are needed to develop the next generation of relaxor ferroelectrics.\n
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\n \n\n \n \n \n \n \n Native oxide reconstructions on AlN and GaN (0001) surfaces.\n \n \n \n\n\n \n Mirrielees, K. J, Dycus, J H., Baker, J. N, Reddy, P., Collazo, R., Sitar, Z., LeBeau, J. M, & Irving, D. L\n\n\n \n\n\n\n J. Appl. Phys., 129(19): 195304. May 2021.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n  \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Mirrielees2021-ur,\n  title     = "Native oxide reconstructions on {AlN} and {GaN} (0001) surfaces",\n  author    = "Mirrielees, Kelsey J and Dycus, J Houston and Baker, Jonathon N\n               and Reddy, Pramod and Collazo, Ram{\\'o}n and Sitar, Zlatko and\n               LeBeau, James M and Irving, Douglas L",\n  abstract  = "Properties of AlN/GaN surfaces are important for realizing the\n               tunability of devices, as the presence of surface states\n               contributes to Fermi level pinning. This pinning can influence\n               the performance of high electron mobility transistors and is\n               also important for passivation of the surface when developing\n               high-power electronic devices. It is widely understood that both\n               AlN and GaN surfaces oxidize. Since there are many possible\n               reconstructions for each surface, it is a challenge to identify\n               the relevant surface reconstructions in advance of a detailed\n               simulation. Because of this, different approaches are often\n               employed to down select initial structures to reduce the\n               computational load. These approaches usually rely on either\n               electron counting rules or oxide stoichiometry, as both of these\n               models tend to lead to structures that are energetically\n               favorable. Here we explore models from these approaches but also\n               explore a reconstruction of the (0001) surface directly observed\n               using scanning transmission electron microscopy with predictive\n               density functional theory simulations. Two compositions of the\n               observed surface reconstruction - one which obeys oxide\n               stoichiometry and one which is cation deficient and obeys\n               electron counting - are compared to reconstructions from the\n               previous work. Furthermore, surface states are directly\n               calculated using hybrid exchange-correlation functionals that\n               correct for the underestimation of the bandgaps in AlN and GaN\n               and improve the predicted positions of surface states within the\n               gap. It is found that cation deficiency in the observed\n               reconstruction yields surface states consistent with the\n               experiment. Based on all of these results, we provide insight\n               into the observed properties of oxidized AlGaN surfaces.",\n  journal   = "J. Appl. Phys.",\n  publisher = "American Institute of Physics Inc.",\n  volume    =  129,\n  number    =  19,\n  pages     = "195304",\n  month     =  may,\n  year      =  2021,\n  keywords  = "LeBeau Group;AFOSR",\n  issn      = "0021-8979",\n  doi       = "10.1063/5.0048820"\n}\n\n
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\n Properties of AlN/GaN surfaces are important for realizing the tunability of devices, as the presence of surface states contributes to Fermi level pinning. This pinning can influence the performance of high electron mobility transistors and is also important for passivation of the surface when developing high-power electronic devices. It is widely understood that both AlN and GaN surfaces oxidize. Since there are many possible reconstructions for each surface, it is a challenge to identify the relevant surface reconstructions in advance of a detailed simulation. Because of this, different approaches are often employed to down select initial structures to reduce the computational load. These approaches usually rely on either electron counting rules or oxide stoichiometry, as both of these models tend to lead to structures that are energetically favorable. Here we explore models from these approaches but also explore a reconstruction of the (0001) surface directly observed using scanning transmission electron microscopy with predictive density functional theory simulations. Two compositions of the observed surface reconstruction - one which obeys oxide stoichiometry and one which is cation deficient and obeys electron counting - are compared to reconstructions from the previous work. Furthermore, surface states are directly calculated using hybrid exchange-correlation functionals that correct for the underestimation of the bandgaps in AlN and GaN and improve the predicted positions of surface states within the gap. It is found that cation deficiency in the observed reconstruction yields surface states consistent with the experiment. Based on all of these results, we provide insight into the observed properties of oxidized AlGaN surfaces.\n
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\n \n\n \n \n \n \n \n Tuning mechanical metastability in FeMnCo medium entropy alloys and a peek into deformable hexagonal close-packed martensite.\n \n \n \n\n\n \n Wei, S., Xu, M., LeBeau, J. M, & Tasan, C. C.\n\n\n \n\n\n\n Appl. Phys. Lett., 119(26): 261905. December 2021.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n  \n \n 2 downloads\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Wei2021-uj,\n  title     = "Tuning mechanical metastability in {FeMnCo} medium entropy\n               alloys and a peek into deformable hexagonal close-packed\n               martensite",\n  author    = "Wei, Shaolou and Xu, Michael and LeBeau, James M and Tasan,\n               Cemal Cem",\n  abstract  = "We report here the compositional dependency of face-centered\n               cubic (FCC) to hexagonal close-packed (HCP) martensitic\n               transformation in FeMnCo medium entropy alloys (MEAs) and\n               insights into the underlying transformation mechanisms. To this\n               end, we designed MEAs with the same Fe-to-Mn ratio and explored\n               the phase stability therein. Higher Co content was found to\n               facilitate the FCC-HCP transformation kinetics. In situ electron\n               backscatter diffraction studies underpinned an FCC-HCP-(new)FCC\n               transformation chain and its underlying atomistic mechanisms\n               were directly explored via aberration-corrected scanning\n               transmission electron microscopy.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "American Institute of Physics",\n  volume    =  119,\n  number    =  26,\n  pages     = "261905",\n  month     =  dec,\n  year      =  2021,\n  keywords  = "Velion Pubs;LeBeau Group",\n  language  = "en",\n  issn      = "0003-6951, 1077-3118",\n  doi       = "10.1063/5.0079981"\n}\n\n
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\n We report here the compositional dependency of face-centered cubic (FCC) to hexagonal close-packed (HCP) martensitic transformation in FeMnCo medium entropy alloys (MEAs) and insights into the underlying transformation mechanisms. To this end, we designed MEAs with the same Fe-to-Mn ratio and explored the phase stability therein. Higher Co content was found to facilitate the FCC-HCP transformation kinetics. In situ electron backscatter diffraction studies underpinned an FCC-HCP-(new)FCC transformation chain and its underlying atomistic mechanisms were directly explored via aberration-corrected scanning transmission electron microscopy.\n
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\n \n\n \n \n \n \n \n Defect-Level Switching for Highly Nonlinear and Hysteretic Electronic Devices.\n \n \n \n\n\n \n Yin, H., Kumar, A., LeBeau, J. M, & Jaramillo, R\n\n\n \n\n\n\n Physical Review Applied, 15(1): 014014. January 2021.\n \n\n\n\n
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@ARTICLE{Yin2021-lo,\n  title    = "{Defect-Level} Switching for Highly Nonlinear and Hysteretic\n              Electronic Devices",\n  author   = "Yin, Han and Kumar, Abinash and LeBeau, James M and Jaramillo, R",\n  journal  = "Physical Review Applied",\n  volume   =  15,\n  number   =  1,\n  pages    = "014014",\n  month    =  jan,\n  year     =  2021,\n  keywords = "LeBeau Group;DHS proposal",\n  issn     = "2331-7019",\n  doi      = "10.1103/PhysRevApplied.15.014014"\n}\n\n
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\n \n\n \n \n \n \n \n Tuning band alignment at a semiconductor-crystalline oxide heterojunction via electrostatic modulation of the interfacial dipole.\n \n \n \n\n\n \n Chrysler, M, Gabel, J, Lee, T., Penn, A N, Matthews, B E, Kepaptsoglou, D M, Ramasse, Q M, Paudel, J R, Sah, R K, Grassi, J D, Zhu, Z, Gray, A X, LeBeau, J M, Spurgeon, S R, Chambers, S A, Sushko, P V, & Ngai, J H\n\n\n \n\n\n\n Physical Review Materials, 5(10): 104603. October 2021.\n \n\n\n\n
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@ARTICLE{Chrysler2021-nh,\n  title    = "Tuning band alignment at a semiconductor-crystalline oxide\n              heterojunction via electrostatic modulation of the interfacial\n              dipole",\n  author   = "Chrysler, M and Gabel, J and Lee, T-L and Penn, A N and Matthews,\n              B E and Kepaptsoglou, D M and Ramasse, Q M and Paudel, J R and\n              Sah, R K and Grassi, J D and Zhu, Z and Gray, A X and LeBeau, J M\n              and Spurgeon, S R and Chambers, S A and Sushko, P V and Ngai, J H",\n  abstract = "We demonstrate that the interfacial dipole associated with\n              bonding across the SrTiO3/Si heterojunction can be tuned through\n              space charge, thereby enabling the band alignment to be altered\n              via doping. Oxygen impurities in Si act as donors that create\n              space charge by transferring electrons across the interface into\n              SrTiO3. The space charge induces an electric field that modifies\n              the interfacial dipole, thereby tuning the band alignment from\n              type-II to type-III. The transferred charge, resulting in\n              built-in electric fields, and change in band alignment are\n              manifested in electrical transport and hard x-ray photoelectron\n              spectroscopy measurements. Ab initio models reveal the interplay\n              between polarization and band offsets. We find that band offsets\n              can be tuned by modulating the density of space charge across the\n              interface. Functionalizing the interface dipole to enable\n              electrostatic altering of band alignment opens new pathways to\n              realize novel behavior in semiconducting heterojunctions.",\n  journal  = "Physical Review Materials",\n  volume   =  5,\n  number   =  10,\n  pages    = "104603",\n  month    =  oct,\n  year     =  2021,\n  keywords = "LeBeau Group",\n  issn     = "2475-9953",\n  doi      = "10.1103/PhysRevMaterials.5.104603"\n}\n\n
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\n We demonstrate that the interfacial dipole associated with bonding across the SrTiO3/Si heterojunction can be tuned through space charge, thereby enabling the band alignment to be altered via doping. Oxygen impurities in Si act as donors that create space charge by transferring electrons across the interface into SrTiO3. The space charge induces an electric field that modifies the interfacial dipole, thereby tuning the band alignment from type-II to type-III. The transferred charge, resulting in built-in electric fields, and change in band alignment are manifested in electrical transport and hard x-ray photoelectron spectroscopy measurements. Ab initio models reveal the interplay between polarization and band offsets. We find that band offsets can be tuned by modulating the density of space charge across the interface. Functionalizing the interface dipole to enable electrostatic altering of band alignment opens new pathways to realize novel behavior in semiconducting heterojunctions.\n
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\n \n\n \n \n \n \n \n Instantaneous nanowelding of ultra‐high temperature ceramics for hypersonics.\n \n \n \n\n\n \n Gai, F., Dycus, J. H., LeBeau, J. M, Walker, L. S, & Corral, E. L\n\n\n \n\n\n\n J. Am. Ceram. Soc., 104(9): 4902–4910. September 2021.\n \n\n\n\n
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@ARTICLE{Gai2021-wi,\n  title     = "Instantaneous nanowelding of ultra‐high temperature ceramics for\n               hypersonics",\n  author    = "Gai, Fangyuan and Dycus, Joseph Houston and LeBeau, James M and\n               Walker, Luke S and Corral, Erica L",\n  abstract  = "Abstract Ultra-high temperature ceramics (UHTCs) are a group of\n               advanced ceramic materials that possess excellent high\n               temperature capabilities, which make them especially suitable\n               for extreme environment engineering applications. As an\n               effective assembling method, joining is frequently required for\n               fabricating sophisticated structures for such applications due\n               to the excessive challenges and costs in producing near-net\n               shapes. Here, we introduce a promising new joining technique to\n               effectively join UHTCs called Instantaneous Nanowelding, which\n               uses direct electric current assisted rapid Joule heating to\n               instantaneously bond hafnium diboride (HfB2) to zirconium\n               diboride (ZrB2) in 1 s down to atomic scale. Our approach is\n               analogous to high temperature spot welding, and the entire\n               process is complete in 10 min, and the instant diffusion occurs\n               in 1 s. Seamless HfB2/ZrB2 interfaces are formed at 1750 for a\n               duration of 1 s. A series of characterizations are done at the\n               interfaces using techniques including SEM, WDS, EBSD, and S/TEM\n               to observe ZrxHf1?xB2 solid solution formation. Highly coherent\n               transition with perfect lattice alignment at atomic scale from\n               ZrB2 to HfB2 is observed using S/TEM, meaning that the two\n               materials are brought to atomic contact.",\n  journal   = "J. Am. Ceram. Soc.",\n  publisher = "Wiley",\n  volume    =  104,\n  number    =  9,\n  pages     = "4902--4910",\n  month     =  sep,\n  year      =  2021,\n  keywords  = "LeBeau Group",\n  copyright = "http://onlinelibrary.wiley.com/termsAndConditions\\#vor",\n  language  = "en",\n  issn      = "0002-7820, 1551-2916",\n  doi       = "10.1111/jace.17866"\n}\n\n
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\n Abstract Ultra-high temperature ceramics (UHTCs) are a group of advanced ceramic materials that possess excellent high temperature capabilities, which make them especially suitable for extreme environment engineering applications. As an effective assembling method, joining is frequently required for fabricating sophisticated structures for such applications due to the excessive challenges and costs in producing near-net shapes. Here, we introduce a promising new joining technique to effectively join UHTCs called Instantaneous Nanowelding, which uses direct electric current assisted rapid Joule heating to instantaneously bond hafnium diboride (HfB2) to zirconium diboride (ZrB2) in 1 s down to atomic scale. Our approach is analogous to high temperature spot welding, and the entire process is complete in 10 min, and the instant diffusion occurs in 1 s. Seamless HfB2/ZrB2 interfaces are formed at 1750 for a duration of 1 s. A series of characterizations are done at the interfaces using techniques including SEM, WDS, EBSD, and S/TEM to observe ZrxHf1?xB2 solid solution formation. Highly coherent transition with perfect lattice alignment at atomic scale from ZrB2 to HfB2 is observed using S/TEM, meaning that the two materials are brought to atomic contact.\n
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\n \n\n \n \n \n \n \n Hybrid molecular beam epitaxy growth of BaTiO$_{3}$ films.\n \n \n \n\n\n \n Nunn, W., Sandlass, S., Wegner, M., Haislmaier, R., Kumar, A., Tangi, M., LeBeau, J. M, Quandt, E., James, R. D, & Jalan, B.\n\n\n \n\n\n\n J. Vac. Sci. Technol. A, 39(4): 040404. July 2021.\n \n\n\n\n
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@ARTICLE{Nunn2021-md,\n  title     = "Hybrid molecular beam epitaxy growth of {BaTiO$_{3}$} films",\n  author    = "Nunn, William and Sandlass, Sara and Wegner, Maike and\n               Haislmaier, Ryan and Kumar, Abinash and Tangi, Malleswararao and\n               LeBeau, James M and Quandt, Eckhard and James, Richard D and\n               Jalan, Bharat",\n  journal   = "J. Vac. Sci. Technol. A",\n  publisher = "American Vacuum Society",\n  volume    =  39,\n  number    =  4,\n  pages     = "040404",\n  month     =  jul,\n  year      =  2021,\n  keywords  = "LeBeau Group",\n  language  = "en",\n  issn      = "0734-2101, 1520-8559",\n  doi       = "10.1116/6.0001140"\n}\n\n
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\n \n\n \n \n \n \n \n Thermoelectric generators for wearable body heat harvesting: Material and device concurrent optimization.\n \n \n \n\n\n \n Nozariasbmarz, A., Suarez, F., Dycus, J H., Cabral, M. J, Lebeau, J. M, Öztürk, M. C, Vashaee, D., Nozariasbmarz, A., Suarez, F., Dycus, J H., Cabral, M. J, Lebeau, J. M, Öztürk, M. C, & Vashaee, D.\n\n\n \n\n\n\n Nano Energy, 67(July): 104265. January 2020.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Nozariasbmarz2020-ct,\n  title     = "Thermoelectric generators for wearable body heat harvesting:\n               Material and device concurrent optimization",\n  author    = "Nozariasbmarz, Amin and Suarez, Francisco and Dycus, J Houston\n               and Cabral, Matthew J and Lebeau, James M and {\\"O}zt{\\"u}rk,\n               Mehmet C and Vashaee, Daryoosh and Nozariasbmarz, Amin and\n               Suarez, Francisco and Dycus, J Houston and Cabral, Matthew J and\n               Lebeau, James M and {\\"O}zt{\\"u}rk, Mehmet C and Vashaee,\n               Daryoosh",\n  abstract  = "Body heat harvesting systems based on thermoelectric generators\n               (TEGs) can play a significant role in wearable electronics\n               intended for continuous, long-term health monitoring. However,\n               to date, the harvested power density from the body using TEGs is\n               limited to a few micro-watts per square centimeter, which is not\n               sufficient to turn on many wearables. The thermoelectric\n               materials research has been mainly focused on enhancing the\n               single parameter zT, which is insufficient to meet the\n               requirements for wearable applications. To develop TEGs that\n               work effectively in wearable devices, one has to consider the\n               material, device, and system requirements concurrently. Due to\n               the lack of an efficient heatsink and the skin thermal\n               resistance, a key challenge to achieving this goal is to design\n               systems that maximize the temperature differential across the\n               TEG while not compromising the body comfort. This requires\n               favoring approaches that deliver the largest possible device\n               thermal resistance relative to the external parasitic\n               resistances. Therefore, materials with low thermal conductivity\n               are critically important to maximize the temperature gradient.\n               Also, to achieve a high boost converter efficiency, wearable\n               TEGs need to have the highest possible output voltage, which\n               calls for a high Seebeck coefficient. At the device level,\n               dimensions of the legs (length versus the base area) and fill\n               factor are both critical parameters to ensure that the parasitic\n               thermal resistances are again negligible compared to the\n               resistance of the module itself. In this study, the concurrent\n               impact of material and device parameters on the efficiency of\n               wearable TEGs is considered. Nanocomposite thermoelectric\n               materials based on bismuth telluride alloys were synthesized\n               using microwave processing and optimized to meet the\n               requirements of wearable TEGs. Microwave energy decrystallized\n               the material leading to a strong reduction of the thermal\n               conductivity while maintaining a high zT at the body\n               temperature. A comprehensive quasi-3D analytical model was\n               developed and used to optimize the material and device\n               parameters. The nanocomposite TEG produced 44 $\\mu$W/cm2 under\n               no air flow condition, and 156.5 $\\mu$W/cm2 under airflow. In\n               comparison to commercial TEGs tested under similar conditions,\n               the nanocomposite based TEGs exhibited 4--7 times higher power\n               density on the human body depending on the convective cooling\n               conditions.",\n  journal   = "Nano Energy",\n  publisher = "Elsevier BV",\n  volume    =  67,\n  number    = "July",\n  pages     = "104265",\n  month     =  jan,\n  year      =  2020,\n  keywords  = "Body heat harvesting; Microwave radiation; Nanocomposites;\n               Self-powered devices; Thermoelectric generators; Wearable\n               technology;LeBeau Group",\n  issn      = "2211-2855",\n  doi       = "10.1016/j.nanoen.2019.104265"\n}\n\n
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\n Body heat harvesting systems based on thermoelectric generators (TEGs) can play a significant role in wearable electronics intended for continuous, long-term health monitoring. However, to date, the harvested power density from the body using TEGs is limited to a few micro-watts per square centimeter, which is not sufficient to turn on many wearables. The thermoelectric materials research has been mainly focused on enhancing the single parameter zT, which is insufficient to meet the requirements for wearable applications. To develop TEGs that work effectively in wearable devices, one has to consider the material, device, and system requirements concurrently. Due to the lack of an efficient heatsink and the skin thermal resistance, a key challenge to achieving this goal is to design systems that maximize the temperature differential across the TEG while not compromising the body comfort. This requires favoring approaches that deliver the largest possible device thermal resistance relative to the external parasitic resistances. Therefore, materials with low thermal conductivity are critically important to maximize the temperature gradient. Also, to achieve a high boost converter efficiency, wearable TEGs need to have the highest possible output voltage, which calls for a high Seebeck coefficient. At the device level, dimensions of the legs (length versus the base area) and fill factor are both critical parameters to ensure that the parasitic thermal resistances are again negligible compared to the resistance of the module itself. In this study, the concurrent impact of material and device parameters on the efficiency of wearable TEGs is considered. Nanocomposite thermoelectric materials based on bismuth telluride alloys were synthesized using microwave processing and optimized to meet the requirements of wearable TEGs. Microwave energy decrystallized the material leading to a strong reduction of the thermal conductivity while maintaining a high zT at the body temperature. A comprehensive quasi-3D analytical model was developed and used to optimize the material and device parameters. The nanocomposite TEG produced 44 $μ$W/cm2 under no air flow condition, and 156.5 $μ$W/cm2 under airflow. In comparison to commercial TEGs tested under similar conditions, the nanocomposite based TEGs exhibited 4–7 times higher power density on the human body depending on the convective cooling conditions.\n
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\n \n\n \n \n \n \n \n Expanding the Dimensions of a Small, Two-Dimensional Diffraction Detector.\n \n \n \n\n\n \n Chen, X., Hauwiller, M. R, Kumar, A., Penn, A. N, & LeBeau, J. M\n\n\n \n\n\n\n Microsc. Microanal., 26(5): 938–943. October 2020.\n \n\n\n\n
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@ARTICLE{Chen2020-gt,\n  title    = "Expanding the Dimensions of a Small, {Two-Dimensional}\n              Diffraction Detector",\n  author   = "Chen, Xi and Hauwiller, Matthew R and Kumar, Abinash and Penn,\n              Aubrey N and LeBeau, James M",\n  abstract = "We report an approach to expand the effective number of pixels\n              available to small, two-dimensional electron detectors. To do so,\n              we acquire subsections of a diffraction pattern that are then\n              accurately stitched together in post-processing. Using an\n              electron microscopy pixel array detector (EMPAD) that has only\n              128 $\\times$ 128 pixels, we show that the field of view can be\n              expanded while achieving high reciprocal-space sampling. Further,\n              we highlight the need to properly account for the detector\n              position (rotation) and the non-orthonormal diffraction shift\n              axes to achieve an accurate reconstruction. Applying the method,\n              we provide examples of spot and convergent beam diffraction\n              patterns acquired with a pixelated detector.",\n  journal  = "Microsc. Microanal.",\n  volume   =  26,\n  number   =  5,\n  pages    = "938--943",\n  month    =  oct,\n  year     =  2020,\n  keywords = "accepted 25 july 2020; diffuse scattering; direct electron\n              cameras; electron diffraction; high dynamic range; received 25\n              march 2020; revised 15 july 2020;LeBeau Group;Velion;AFOSR",\n  issn     = "1431-9276, 1435-8115",\n  doi      = "10.1017/S1431927620024277"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n We report an approach to expand the effective number of pixels available to small, two-dimensional electron detectors. To do so, we acquire subsections of a diffraction pattern that are then accurately stitched together in post-processing. Using an electron microscopy pixel array detector (EMPAD) that has only 128 $×$ 128 pixels, we show that the field of view can be expanded while achieving high reciprocal-space sampling. Further, we highlight the need to properly account for the detector position (rotation) and the non-orthonormal diffraction shift axes to achieve an accurate reconstruction. Applying the method, we provide examples of spot and convergent beam diffraction patterns acquired with a pixelated detector.\n
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\n \n\n \n \n \n \n \n Observing relaxation in device quality InGaN templates by TEM techniques.\n \n \n \n\n\n \n Eldred, T. B, Abdelhamid, M., Reynolds, J G, El-Masry, N A, LeBeau, J. M, & Bedair, S. M\n\n\n \n\n\n\n Appl. Phys. Lett., 116(10): 102104. March 2020.\n \n\n\n\n
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@ARTICLE{Eldred2020-hk,\n  title     = "Observing relaxation in device quality {InGaN} templates by\n               {TEM} techniques",\n  author    = "Eldred, Tim B and Abdelhamid, Mostafa and Reynolds, J G and\n               El-Masry, N A and LeBeau, James M and Bedair, Salah M",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "AIP Publishing LLC",\n  volume    =  116,\n  number    =  10,\n  pages     = "102104",\n  month     =  mar,\n  year      =  2020,\n  keywords  = "LeBeau Group;Velion",\n  issn      = "0003-6951",\n  doi       = "10.1063/1.5139269"\n}\n\n
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\n \n\n \n \n \n \n \n On the redistribution of charge in La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 multilayer thin films.\n \n \n \n\n\n \n Penn, A. N, Koohfar, S., Kumah, D. P, & LeBeau, J. M\n\n\n \n\n\n\n AIP Adv., 10(4): 045113. April 2020.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Penn2020-yp,\n  title     = "On the redistribution of charge in\n               {La0.7Sr0.3CrO3/La0.7Sr0.3MnO3} multilayer thin films",\n  author    = "Penn, Aubrey N and Koohfar, Sanaz and Kumah, Divine P and\n               LeBeau, James M",\n  abstract  = "The atomic and electronic structures of La0.7Sr0.3MnO3\n               (LSMO)/La0.7Sr0.3CrO3 (LSCO) multilayer thin films are\n               investigated using aberration corrected scanning transmission\n               electron microscopy (STEM) imaging and spectroscopy. Atomic\n               resolution high angle annular dark-field reveals that LSMO\n               layers have an expanded out-of-plane lattice parameter compared\n               to compressed LSCO layers, contrasting with x-ray diffraction\n               measurements. The expansion is found to result from preferential\n               oxygen vacancy formation in LSMO during STEM sample preparation\n               as determined by electron energy-loss spectroscopy. The La/Sr\n               atom column intensity is also found to oscillate by about 4\\%\n               between the LSMO and LSCO layers, indicative of La/Sr\n               concentration variation. Using energy-dispersive x-ray\n               spectroscopy in combination with image simulations, we confirm\n               the La/Sr inhomogeneity and elucidate the origin of charge\n               redistribution within the multilayer. These results illuminate\n               the sensitivity of the technique to subtle structural, chemical,\n               and electronic features that can arise to compensate charge\n               imbalances in complex oxide heterostructures.",\n  journal   = "AIP Adv.",\n  publisher = "American Institute of Physics",\n  volume    =  10,\n  number    =  4,\n  pages     = "045113",\n  month     =  apr,\n  year      =  2020,\n  keywords  = "LeBeau Group;Velion;DHS proposal",\n  doi       = "10.1063/1.5140352"\n}\n\n
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\n The atomic and electronic structures of La0.7Sr0.3MnO3 (LSMO)/La0.7Sr0.3CrO3 (LSCO) multilayer thin films are investigated using aberration corrected scanning transmission electron microscopy (STEM) imaging and spectroscopy. Atomic resolution high angle annular dark-field reveals that LSMO layers have an expanded out-of-plane lattice parameter compared to compressed LSCO layers, contrasting with x-ray diffraction measurements. The expansion is found to result from preferential oxygen vacancy formation in LSMO during STEM sample preparation as determined by electron energy-loss spectroscopy. The La/Sr atom column intensity is also found to oscillate by about 4% between the LSMO and LSCO layers, indicative of La/Sr concentration variation. Using energy-dispersive x-ray spectroscopy in combination with image simulations, we confirm the La/Sr inhomogeneity and elucidate the origin of charge redistribution within the multilayer. These results illuminate the sensitivity of the technique to subtle structural, chemical, and electronic features that can arise to compensate charge imbalances in complex oxide heterostructures.\n
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\n \n\n \n \n \n \n \n Cathodoluminescence of silicon doped aluminum nitride with scanning transmission electron microscopy.\n \n \n \n\n\n \n Hauwiller, M. R, Stowe, D., Eldred, T. B, Mita, S., Collazo, R., Sitar, Z., & Lebeau, J.\n\n\n \n\n\n\n APL Materials, 8(9). 2020.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n  \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Hauwiller2020-sz,\n  title     = "Cathodoluminescence of silicon doped aluminum nitride with\n               scanning transmission electron microscopy",\n  author    = "Hauwiller, Matthew R and Stowe, David and Eldred, Timothy B and\n               Mita, Seiji and Collazo, Ramon and Sitar, Zlatko and Lebeau,\n               James",\n  abstract  = "\\copyright{} 2020 Author(s). Here, we apply cathodoluminescence\n               in scanning transmission electron microscopy to infer the\n               influence of dislocation strain fields on the formation of point\n               defect complexes in Si doped AlN. In addition to identifying\n               non-radiative recombination centers, tracking Si related defect\n               emission energies reveals a red-shift at threading dislocations.\n               We discuss these results in the context of multiple Si-vacancy\n               defect complexes that can form and the influence of local strain\n               on their formation energies. By correlating the electronic and\n               structural properties at the nanoscale, cathodoluminescence\n               elucidates the inhomogeneity of defect complexes in Si doped AlN\n               and offers the potential for strain engineering to control the\n               defect energy formation landscape.",\n  journal   = "APL Materials",\n  publisher = "AIP Publishing, LLC",\n  volume    =  8,\n  number    =  9,\n  year      =  2020,\n  keywords  = "LeBeau Group;Velion;AFOSR;DHS proposal",\n  issn      = "2166-532X",\n  doi       = "10.1063/5.0019863"\n}\n\n
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\n © 2020 Author(s). Here, we apply cathodoluminescence in scanning transmission electron microscopy to infer the influence of dislocation strain fields on the formation of point defect complexes in Si doped AlN. In addition to identifying non-radiative recombination centers, tracking Si related defect emission energies reveals a red-shift at threading dislocations. We discuss these results in the context of multiple Si-vacancy defect complexes that can form and the influence of local strain on their formation energies. By correlating the electronic and structural properties at the nanoscale, cathodoluminescence elucidates the inhomogeneity of defect complexes in Si doped AlN and offers the potential for strain engineering to control the defect energy formation landscape.\n
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\n \n\n \n \n \n \n \n Formation of large-area MoS$_{2}$ thin films by oxygen-catalyzed sulfurization of Mo thin films.\n \n \n \n\n\n \n Jo, S. S., Li, Y., Singh, A., Kumar, A., Frisone, S., LeBeau, J. M, & Jaramillo, R.\n\n\n \n\n\n\n J. Vac. Sci. Technol. A, 38(1): 013405. January 2020.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Jo2020-nq,\n  title     = "Formation of large-area {MoS$_{2}$} thin films by\n               oxygen-catalyzed sulfurization of Mo thin films",\n  author    = "Jo, Seong Soon and Li, Yifei and Singh, Akshay and Kumar,\n               Abinash and Frisone, Sam and LeBeau, James M and Jaramillo,\n               Rafael",\n  abstract  = "\\copyright{} 2019 Author(s). While transition metal\n               dichalcogenide (TMD) thin films are most commonly synthesized by\n               vapor transport using solid metal oxide precursors, directly\n               converting metal thin films to TMDs may be more scalable and\n               controllable, e.g., to enable large-area coating by vacuum\n               deposition. The thermodynamics are favorable for MoS2 formation\n               from Mo in sulfur-rich environments, but sulfurization tends to\n               be slow and the product is highly dependent on the chemical\n               pathway taken. Here, the authors report on the role of trace\n               oxygen gas (O2) for the sulfurization of Mo films. They study\n               the formation of MoS2 from Mo films in H2S vapor, between 350\n               and 500 °C and with varying levels of O2. They find that the\n               presence of trace levels of O2 accelerates the crystallization\n               of MoS2 and affects the layer orientation, without changing the\n               kinetics of mass transport or the final film composition. O2\n               acts as a catalyst to promote the crystallization of MoS2 at\n               lower temperatures than otherwise possible. These results\n               provide new insights into the growth of MoS2 by sulfurization\n               and suggest that introducing an appropriate catalyst during\n               chalcogenide phase formation could enable new processes for\n               making homogeneous, large-area MoS2 films at low processing\n               temperature on a variety of substrates.",\n  journal   = "J. Vac. Sci. Technol. A",\n  publisher = "American Vacuum Society",\n  volume    =  38,\n  number    =  1,\n  pages     = "013405",\n  month     =  jan,\n  year      =  2020,\n  keywords  = "LeBeau Group;Velion",\n  issn      = "0734-2101, 1520-8559",\n  doi       = "10.1116/1.5132748"\n}\n\n
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\n © 2019 Author(s). While transition metal dichalcogenide (TMD) thin films are most commonly synthesized by vapor transport using solid metal oxide precursors, directly converting metal thin films to TMDs may be more scalable and controllable, e.g., to enable large-area coating by vacuum deposition. The thermodynamics are favorable for MoS2 formation from Mo in sulfur-rich environments, but sulfurization tends to be slow and the product is highly dependent on the chemical pathway taken. Here, the authors report on the role of trace oxygen gas (O2) for the sulfurization of Mo films. They study the formation of MoS2 from Mo films in H2S vapor, between 350 and 500 °C and with varying levels of O2. They find that the presence of trace levels of O2 accelerates the crystallization of MoS2 and affects the layer orientation, without changing the kinetics of mass transport or the final film composition. O2 acts as a catalyst to promote the crystallization of MoS2 at lower temperatures than otherwise possible. These results provide new insights into the growth of MoS2 by sulfurization and suggest that introducing an appropriate catalyst during chalcogenide phase formation could enable new processes for making homogeneous, large-area MoS2 films at low processing temperature on a variety of substrates.\n
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\n \n\n \n \n \n \n \n Suspended single-crystalline oxide structures on silicon through wet-etch techniques: Effects of oxygen vacancies and dislocations on etch rates.\n \n \n \n\n\n \n Lim, Z. H., Chrysler, M., Kumar, A., Mauthe, J. P, Kumah, D. P, Richardson, C., LeBeau, J. M, & Ngai, J. H\n\n\n \n\n\n\n J. Vac. Sci. Technol. A, 38(1): 013406. January 2020.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n  \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Lim2020-eo,\n  title     = "Suspended single-crystalline oxide structures on silicon through\n               wet-etch techniques: Effects of oxygen vacancies and\n               dislocations on etch rates",\n  author    = "Lim, Zheng Hui and Chrysler, Matthew and Kumar, Abinash and\n               Mauthe, Jacob P and Kumah, Divine P and Richardson, Chris and\n               LeBeau, James M and Ngai, Joseph H",\n  journal   = "J. Vac. Sci. Technol. A",\n  publisher = "American Vacuum Society",\n  volume    =  38,\n  number    =  1,\n  pages     = "013406",\n  month     =  jan,\n  year      =  2020,\n  keywords  = "LeBeau Group",\n  issn      = "0734-2101",\n  doi       = "10.1116/1.5135035"\n}\n\n
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\n  \n 2019\n \n \n (10)\n \n \n
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\n \n\n \n \n \n \n \n Transmission Electron Microscopy (STEM and TEM).\n \n \n \n\n\n \n Grimley, E. D, & LeBeau, J. M\n\n\n \n\n\n\n In Ferroelectricity in Doped Hafnium Oxide: Materials, Properties and Devices, pages 317–340. Elsevier, 2019.\n \n\n\n\n
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@INCOLLECTION{Grimley2019-fv,\n  title     = "Transmission Electron Microscopy ({STEM} and {TEM})",\n  booktitle = "Ferroelectricity in Doped Hafnium Oxide: Materials, Properties\n               and Devices",\n  author    = "Grimley, Everett D and LeBeau, James M",\n  publisher = "Elsevier",\n  pages     = "317--340",\n  year      =  2019,\n  keywords  = "LeBeau Group",\n  isbn      = "9780081024300",\n  doi       = "10.1016/b978-0-08-102430-0.00015-2"\n}\n\n
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\n \n\n \n \n \n \n \n Engineering Efficient Photon Upconversion in Semiconductor Heterostructures.\n \n \n \n\n\n \n Milleville, C. C, Chen, E. Y, Lennon, K. R, Cleveland, J. M, Kumar, A., Zhang, J., Bork, J. A, Tessier, A., LeBeau, J. M, Chase, D B., Zide, J. M O, & Doty, M. F\n\n\n \n\n\n\n ACS Nano, 13(1): 489–497. January 2019.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Milleville2019-ab,\n  title    = "Engineering Efficient Photon Upconversion in Semiconductor\n              Heterostructures",\n  author   = "Milleville, Christopher C and Chen, Eric Y and Lennon, Kyle R and\n              Cleveland, Jill M and Kumar, Abinash and Zhang, Jing and Bork,\n              James A and Tessier, Ansel and LeBeau, James M and Chase, D Bruce\n              and Zide, Joshua M O and Doty, Matthew F",\n  abstract = "Photon upconversion is a photophysical process in which two\n              low-energy photons are converted into one high-energy photon.\n              Photon upconversion has broad appeal for a range of applications\n              from biomedical imaging and targeted drug release to solar energy\n              harvesting. Current upconversion nanosystems, including\n              lanthanide-doped nanocrystals and triplet-triplet annihilation\n              molecules, have achieved upconversion quantum yields on the order\n              of 10-30\\%. However, the performance of these materials is\n              hampered by inherently narrow absorption cross sections and fixed\n              energy levels originating in atomic, ionic, or molecular states.\n              Semiconductors, on the other hand, have inherently wide\n              absorption cross sections. Moreover, recent advances enable the\n              synthesis of colloidal semiconductor nanoparticles with complex\n              heterostructures that can control band alignments and tune\n              optical properties. We synthesize and characterize a\n              three-component heterostructure that successfully upconverts\n              photons under continuous-wave illumination and solar-relevant\n              photon fluxes. The heterostructure is composed of two cadmium\n              selenide quantum dots (QDs), an absorber and emitter, spatially\n              separated by a cadmium sulfide nanorod (NR). We demonstrate that\n              the principles of semiconductor heterostructure engineering can\n              be applied to engineer improved upconversion efficiency. We first\n              eliminate electron trap states near the surface of the absorbing\n              QD and then tailor the band gap of the NR such that charge\n              carriers are funneled to the emitting QD. When combined, these\n              two changes result in a 100-fold improvement in photon\n              upconversion performance.",\n  journal  = "ACS Nano",\n  volume   =  13,\n  number   =  1,\n  pages    = "489--497",\n  month    =  jan,\n  year     =  2019,\n  keywords = "core/rod/emitter; coupled quantum dots; nanostructures;\n              semiconductors; solar energy; upconversion;LeBeau Group",\n  language = "en",\n  issn     = "1936-0851, 1936-086X",\n  pmid     = "30576110",\n  doi      = "10.1021/acsnano.8b07062"\n}\n\n
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\n Photon upconversion is a photophysical process in which two low-energy photons are converted into one high-energy photon. Photon upconversion has broad appeal for a range of applications from biomedical imaging and targeted drug release to solar energy harvesting. Current upconversion nanosystems, including lanthanide-doped nanocrystals and triplet-triplet annihilation molecules, have achieved upconversion quantum yields on the order of 10-30%. However, the performance of these materials is hampered by inherently narrow absorption cross sections and fixed energy levels originating in atomic, ionic, or molecular states. Semiconductors, on the other hand, have inherently wide absorption cross sections. Moreover, recent advances enable the synthesis of colloidal semiconductor nanoparticles with complex heterostructures that can control band alignments and tune optical properties. We synthesize and characterize a three-component heterostructure that successfully upconverts photons under continuous-wave illumination and solar-relevant photon fluxes. The heterostructure is composed of two cadmium selenide quantum dots (QDs), an absorber and emitter, spatially separated by a cadmium sulfide nanorod (NR). We demonstrate that the principles of semiconductor heterostructure engineering can be applied to engineer improved upconversion efficiency. We first eliminate electron trap states near the surface of the absorbing QD and then tailor the band gap of the NR such that charge carriers are funneled to the emitting QD. When combined, these two changes result in a 100-fold improvement in photon upconversion performance.\n
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\n \n\n \n \n \n \n \n Multiple Epsilon-Near-Zero Resonances in Multilayered Cadmium Oxide: Designing Metamaterial-Like Optical Properties in Monolithic Materials.\n \n \n \n\n\n \n Kelley, K. P, Runnerstrom, E. L, Sachet, E., Shelton, C. T, Grimley, E. D, Klump, A., LeBeau, J. M, Sitar, Z., Suen, J. Y, Padilla, W. J, & Maria, J.\n\n\n \n\n\n\n ACS Photonics, in press: acsphotonics.9b00367. 2019.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Kelley2019-ag,\n  title    = "Multiple {Epsilon-Near-Zero} Resonances in Multilayered Cadmium\n              Oxide: Designing {Metamaterial-Like} Optical Properties in\n              Monolithic Materials",\n  author   = "Kelley, Kyle P and Runnerstrom, Evan L and Sachet, Edward and\n              Shelton, Christopher T and Grimley, Everett D and Klump, Andrew\n              and LeBeau, James M and Sitar, Zlatko and Suen, Jonathan Y and\n              Padilla, Willie J and Maria, Jon-Paul",\n  journal  = "ACS Photonics",\n  volume   = "in press",\n  pages    = "acsphotonics.9b00367",\n  year     =  2019,\n  keywords = "and; bio; cdo; chemistry communities; epsilon-near-zero; he\n              ability to engineer; infrared; ir; is fundamentally important to;\n              light; matter interactions across the; nanophotonics; photonics;\n              physics; plasmonics; science; the materials; thin fi lm;LeBeau\n              Group",\n  issn     = "2330-4022",\n  doi      = "10.1021/acsphotonics.9b00367"\n}\n\n
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\n \n\n \n \n \n \n \n Confinement of magnetism in atomically thin La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 heterostructures.\n \n \n \n\n\n \n Koohfar, S., Georgescu, A. B, Penn, A. N, LeBeau, J. M, Arenholz, E., & Kumah, D. P\n\n\n \n\n\n\n npj Quantum Materials, 4(1): 25. December 2019.\n \n\n\n\n
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@ARTICLE{Koohfar2019-oh,\n  title    = "Confinement of magnetism in atomically thin\n              {La0.7Sr0.3CrO3/La0.7Sr0.3MnO3} heterostructures",\n  author   = "Koohfar, Sanaz and Georgescu, Alexandru B and Penn, Aubrey N and\n              LeBeau, James M and Arenholz, Elke and Kumah, Divine P",\n  journal  = "npj Quantum Materials",\n  volume   =  4,\n  number   =  1,\n  pages    = "25",\n  month    =  dec,\n  year     =  2019,\n  keywords = "LeBeau Group",\n  issn     = "2397-4648",\n  doi      = "10.1038/s41535-019-0164-1"\n}\n\n
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\n \n\n \n \n \n \n \n The role of transient surface morphology on composition control in AlGaN layers and wells.\n \n \n \n\n\n \n Houston Dycus, J, Washiyama, S., Eldred, T. B, Guan, Y., Kirste, R., Mita, S., Sitar, Z., Collazo, R., & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 114(3): 031602. January 2019.\n \n\n\n\n
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@ARTICLE{Houston_Dycus2019-ep,\n  title    = "The role of transient surface morphology on composition control\n              in {AlGaN} layers and wells",\n  author   = "Houston Dycus, J and Washiyama, Shun and Eldred, Tim B and Guan,\n              Yan and Kirste, Ronny and Mita, Seiji and Sitar, Zlatko and\n              Collazo, Ramon and LeBeau, James M",\n  abstract = "1. Houston Dycus, J., Washiyama, S., Eldred, T. B., Guan, Y.,\n              Kirste, R., Mita, S., Sitar, Z., Collazo, R., and LeBeau, J. M.\n              ``The Role of Transient Surface Morphology on Composition Control\n              in AlGaN Layers and Wells'' Applied Physics Letters 114, 031602.\n              (2019) doi:10.1063/1.5063933",\n  journal  = "Appl. Phys. Lett.",\n  volume   =  114,\n  number   =  3,\n  pages    = "031602",\n  month    =  jan,\n  year     =  2019,\n  keywords = "LeBeau Group;AFOSR",\n  issn     = "0003-6951",\n  doi      = "10.1063/1.5063933"\n}\n\n
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\n 1. Houston Dycus, J., Washiyama, S., Eldred, T. B., Guan, Y., Kirste, R., Mita, S., Sitar, Z., Collazo, R., and LeBeau, J. M. ``The Role of Transient Surface Morphology on Composition Control in AlGaN Layers and Wells'' Applied Physics Letters 114, 031602. (2019) doi:10.1063/1.5063933\n
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\n \n\n \n \n \n \n \n Effect of oxygen stoichiometry on the magnetization profiles and negative magnetization in LSMO thin films.\n \n \n \n\n\n \n Trappen, R., Grutter, A. J, Huang, C., Penn, A., Mottaghi, N., Yousefi, S., Haertter, A., Kumari, S., LeBeau, J. M, Kirby, B. J, & Holcomb, M. B\n\n\n \n\n\n\n J. Appl. Phys., 126(10): 105301. September 2019.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Trappen2019-oq,\n  title     = "Effect of oxygen stoichiometry on the magnetization profiles and\n               negative magnetization in {LSMO} thin films",\n  author    = "Trappen, Robbyn and Grutter, Alexander J and Huang, Chih-Yeh and\n               Penn, Aubrey and Mottaghi, Navid and Yousefi, Saeed and\n               Haertter, Allison and Kumari, Shalini and LeBeau, James M and\n               Kirby, Brian J and Holcomb, Mikel B",\n  abstract  = "The depth-dependent magnetization in thin film oxygen\n               stoichiometric and oxygen-deficient La0.7Sr0.3MnO3 is\n               investigated by using polarized neutron reflectivity and DC bulk\n               magnetometry. The polari...",\n  journal   = "J. Appl. Phys.",\n  publisher = "AIP Publishing LLC",\n  volume    =  126,\n  number    =  10,\n  pages     = "105301",\n  month     =  sep,\n  year      =  2019,\n  keywords  = "LeBeau Group",\n  issn      = "0021-8979",\n  doi       = "10.1063/1.5111858"\n}\n\n
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\n The depth-dependent magnetization in thin film oxygen stoichiometric and oxygen-deficient La0.7Sr0.3MnO3 is investigated by using polarized neutron reflectivity and DC bulk magnetometry. The polari...\n
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\n \n\n \n \n \n \n \n Charge Transfer and Built-in Electric Fields between a Crystalline Oxide and Silicon.\n \n \n \n\n\n \n Lim, Z H, Quackenbush, N F, Penn, A N, Chrysler, M, Bowden, M, Zhu, Z, Ablett, J M, Lee, T., LeBeau, J M, Woicik, J C, Sushko, P V, Chambers, S A, & Ngai, J H\n\n\n \n\n\n\n Phys. Rev. Lett., 123(2): 026805. 2019.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n  \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Lim2019-jf,\n  title     = "Charge Transfer and Built-in Electric Fields between a\n               Crystalline Oxide and Silicon",\n  author    = "Lim, Z H and Quackenbush, N F and Penn, A N and Chrysler, M and\n               Bowden, M and Zhu, Z and Ablett, J M and Lee, T-L and LeBeau, J\n               M and Woicik, J C and Sushko, P V and Chambers, S A and Ngai, J\n               H",\n  journal   = "Phys. Rev. Lett.",\n  publisher = "American Physical Society",\n  volume    =  123,\n  number    =  2,\n  pages     = "026805",\n  year      =  2019,\n  keywords  = "doi:10.1103/PhysRevLett.123.026805 url:https://doi;LeBeau\n               Group;DHS proposal",\n  issn      = "0031-9007",\n  doi       = "10.1103/PhysRevLett.123.026805"\n}\n\n
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\n \n\n \n \n \n \n \n Charge confinement and thermal transport processes in modulation-doped epitaxial crystals lacking lattice interfaces.\n \n \n \n\n\n \n Radue, E., Runnerstrom, E. L, Kelley, K. P, Rost, C. M, Donovan, B. F, Grimley, E. D, LeBeau, J. M, Maria, J., & Hopkins, P. E\n\n\n \n\n\n\n Physical Review Materials, 3(3): 032201. 2019.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Radue2019-cv,\n  title     = "Charge confinement and thermal transport processes in\n               modulation-doped epitaxial crystals lacking lattice interfaces",\n  author    = "Radue, Elizabeth and Runnerstrom, Evan L and Kelley, Kyle P and\n               Rost, Christina M and Donovan, Brian F and Grimley, Everett D\n               and LeBeau, James M and Maria, Jon-Paul and Hopkins, Patrick E",\n  journal   = "Physical Review Materials",\n  publisher = "American Physical Society",\n  volume    =  3,\n  number    =  3,\n  pages     = "032201",\n  year      =  2019,\n  keywords  = "doi:10.1103/PhysRevMaterials.3.032201 url:https://;LeBeau\n               Group;DHS proposal",\n  issn      = "2475-9953",\n  doi       = "10.1103/PhysRevMaterials.3.032201"\n}\n\n
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\n \n\n \n \n \n \n \n Thermochemical model on the carbothermal reduction of oxides during spark plasma sintering of zirconium diboride.\n \n \n \n\n\n \n Pham, D., Dycus, J. H, LeBeau, J. M, Manga, V. R, Muralidharan, K., & Corral, E. L\n\n\n \n\n\n\n J. Am. Ceram. Soc., 102(2): 757–767. 2019.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Pham2019-ix,\n  title    = "Thermochemical model on the carbothermal reduction of oxides\n              during spark plasma sintering of zirconium diboride",\n  author   = "Pham, David and Dycus, Joseph H and LeBeau, James M and Manga,\n              Venkateswara R and Muralidharan, Krishna and Corral, Erica L",\n  abstract = "Abstract Carbon was used to reduce oxides in spark plasma\n              sintered ZrB2 ultra-high temperature ceramics. A thermodynamic\n              model was used to evaluate the reducing reactions to remove B2O3\n              and ZrO2 from the powder. Powder oxygen content was measured and\n              carbon additions of 0.5 and 0.75 wt\\% were used. A C--ZrO2 pseudo\n              binary diagram, ZrO2--B2O3--C pseudo ternaries, and Zr--C--O\n              potential phase diagrams were generated to show how the reactions\n              can be related to an open system experiment in the tube furnace.\n              Scanning transmission electron microscopy identified impurity\n              phases composed of amorphous Zr--B--O with lamellar BN and a\n              Zr--C--O ternary model was calculated under SPS sintering\n              conditions at 1900°C and 6 Pa to understand how oxides can be\n              retained in the microstructure.",\n  journal  = "J. Am. Ceram. Soc.",\n  volume   =  102,\n  number   =  2,\n  pages    = "757--767",\n  year     =  2019,\n  keywords = "Field Assisted Sintering Technology (FAST); phase diagrams; spark\n              plasma sintering; ultra-high temperature ceramics;LeBeau Group",\n  doi      = "10.1111/jace.15911"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Abstract Carbon was used to reduce oxides in spark plasma sintered ZrB2 ultra-high temperature ceramics. A thermodynamic model was used to evaluate the reducing reactions to remove B2O3 and ZrO2 from the powder. Powder oxygen content was measured and carbon additions of 0.5 and 0.75 wt% were used. A C–ZrO2 pseudo binary diagram, ZrO2–B2O3–C pseudo ternaries, and Zr–C–O potential phase diagrams were generated to show how the reactions can be related to an open system experiment in the tube furnace. Scanning transmission electron microscopy identified impurity phases composed of amorphous Zr–B–O with lamellar BN and a Zr–C–O ternary model was calculated under SPS sintering conditions at 1900°C and 6 Pa to understand how oxides can be retained in the microstructure.\n
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\n \n\n \n \n \n \n \n Giant piezoelectricity of Sm-doped Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-PbTiO$_{3}$ single crystals.\n \n \n \n\n\n \n Li, F., Cabral, M. J, Xu, B., Cheng, Z., Dickey, E. C, LeBeau, J. M, Wang, J., Luo, J., Taylor, S., Hackenberger, W., Bellaiche, L., Xu, Z., Chen, L., Shrout, T. R, & Zhang, S.\n\n\n \n\n\n\n Science, 364(6437): 264–268. April 2019.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Li2019-bs,\n  title    = "Giant piezoelectricity of Sm-doped\n              {Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$-PbTiO$_{3}$} single crystals",\n  author   = "Li, Fei and Cabral, Matthew J and Xu, Bin and Cheng, Zhenxiang\n              and Dickey, Elizabeth C and LeBeau, James M and Wang, Jianli and\n              Luo, Jun and Taylor, Samuel and Hackenberger, Wesley and\n              Bellaiche, Laurent and Xu, Zhuo and Chen, Long-Qing and Shrout,\n              Thomas R and Zhang, Shujun",\n  abstract = "High-performance piezoelectrics benefit transducers and sensors\n              in a variety of electromechanical applications. The materials\n              with the highest piezoelectric charge coefficients (d 33) are\n              relaxor-PbTiO3 crystals, which were discovered two decades ago.\n              We successfully grew Sm-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Sm-PMN-PT)\n              single crystals with even higher d 33 values ranging from 3400 to\n              4100 picocoulombs per newton, with variation below 20\\% over the\n              as-grown crystal boule, exhibiting good property uniformity. We\n              characterized the Sm-PMN-PT on the atomic scale with scanning\n              transmission electron microscopy and made first-principles\n              calculations to determine that the giant piezoelectric properties\n              arise from the enhanced local structural heterogeneity introduced\n              by Sm3+ dopants. Rare-earth doping is thus identified as a\n              general strategy for introducing local structural heterogeneity\n              in order to enhance the piezoelectricity of relaxor ferroelectric\n              crystals.",\n  journal  = "Science",\n  volume   =  364,\n  number   =  6437,\n  pages    = "264--268",\n  month    =  apr,\n  year     =  2019,\n  keywords = "LeBeau Group",\n  language = "en",\n  issn     = "0036-8075, 1095-9203",\n  pmid     = "31000659",\n  doi      = "10.1126/science.aaw2781"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n High-performance piezoelectrics benefit transducers and sensors in a variety of electromechanical applications. The materials with the highest piezoelectric charge coefficients (d 33) are relaxor-PbTiO3 crystals, which were discovered two decades ago. We successfully grew Sm-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Sm-PMN-PT) single crystals with even higher d 33 values ranging from 3400 to 4100 picocoulombs per newton, with variation below 20% over the as-grown crystal boule, exhibiting good property uniformity. We characterized the Sm-PMN-PT on the atomic scale with scanning transmission electron microscopy and made first-principles calculations to determine that the giant piezoelectric properties arise from the enhanced local structural heterogeneity introduced by Sm3+ dopants. Rare-earth doping is thus identified as a general strategy for introducing local structural heterogeneity in order to enhance the piezoelectricity of relaxor ferroelectric crystals.\n
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\n  \n 2018\n \n \n (13)\n \n \n
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\n \n\n \n \n \n \n \n A deep convolutional neural network to analyze position averaged convergent beam electron diffraction patterns.\n \n \n \n\n\n \n Xu, W., & LeBeau, J M\n\n\n \n\n\n\n Ultramicroscopy, 188: 59–69. May 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n  \n \n 2 downloads\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Xu2018-jj,\n  title    = "A deep convolutional neural network to analyze position averaged\n              convergent beam electron diffraction patterns",\n  author   = "Xu, Weizong and LeBeau, J M",\n  abstract = "We establish a series of deep convolutional neural networks to\n              automatically analyze position averaged convergent beam electron\n              diffraction patterns. The networks first calibrate the zero-order\n              disk size, center position, and rotation without the need for\n              pretreating the data. With the aligned data, additional networks\n              then measure the sample thickness and tilt. The performance of\n              the network is explored as a function of a variety of variables\n              including thickness, tilt, and dose. A methodology to explore the\n              response of the neural network to various pattern features is\n              also presented. Processing patterns at a rate of $\\sim$0.1\n              s/pattern, the network is shown to be orders of magnitude faster\n              than a brute force method while maintaining accuracy. The\n              approach is thus suitable for automatically processing big, 4D\n              STEM data. We also discuss the generality of the method to other\n              materials/orientations as well as a hybrid approach that combines\n              the features of the neural network with least squares fitting for\n              even more robust analysis. The source code is available at\n              https://github.com/subangstrom/DeepDiffraction.",\n  journal  = "Ultramicroscopy",\n  volume   =  188,\n  pages    = "59--69",\n  month    =  may,\n  year     =  2018,\n  keywords = "automation; convolutional neural networks; electron diffraction;\n              machine learning; pacbed; position averaged convergent\n              beam;LeBeau Group;AFOSR;Amazon",\n  language = "en",\n  issn     = "0304-3991, 1879-2723",\n  pmid     = "29554487",\n  arxivid  = "1708.00855",\n  doi      = "10.1016/j.ultramic.2018.03.004"\n}\n\n
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\n We establish a series of deep convolutional neural networks to automatically analyze position averaged convergent beam electron diffraction patterns. The networks first calibrate the zero-order disk size, center position, and rotation without the need for pretreating the data. With the aligned data, additional networks then measure the sample thickness and tilt. The performance of the network is explored as a function of a variety of variables including thickness, tilt, and dose. A methodology to explore the response of the neural network to various pattern features is also presented. Processing patterns at a rate of $∼$0.1 s/pattern, the network is shown to be orders of magnitude faster than a brute force method while maintaining accuracy. The approach is thus suitable for automatically processing big, 4D STEM data. We also discuss the generality of the method to other materials/orientations as well as a hybrid approach that combines the features of the neural network with least squares fitting for even more robust analysis. The source code is available at https://github.com/subangstrom/DeepDiffraction.\n
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\n \n\n \n \n \n \n \n Probing collective oscillation of $d$-orbital electrons at the nanoscale.\n \n \n \n\n\n \n Dhall, R., Vigil-Fowler, D., Houston Dycus, J, Kirste, R., Mita, S., Sitar, Z., Collazo, R., & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 112(6): 1708.03817. February 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n  \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Dhall2018-gk,\n  title    = "Probing collective oscillation of $d$-orbital electrons at the\n              nanoscale",\n  author   = "Dhall, Rohan and Vigil-Fowler, Derek and Houston Dycus, J and\n              Kirste, Ronny and Mita, Seiji and Sitar, Zlatko and Collazo,\n              Ramon and LeBeau, James M",\n  abstract = "Here we demonstrate that high energy electrons can be used to\n              explore the collective oscillation of $s$, $p$, and $d$ orbital\n              electrons at the nanometer length scale. Using epitaxial\n              AlGaN/AlN quantum wells as a test system, we observe the\n              emergence of additional features in the loss spectrum with\n              increasing Ga content. A comparison of the observed spectra with\n              ab--initio theory reveals the origin of these spectral features\n              is attributed to 3$d$--electrons contributed by Ga. We find that\n              these modes differ in energy from the valence electron plasmons\n              in Al$_\\{1-x\\}$Ga$_x$N due to the different polarizability of the\n              $d$ electrons. Finally, we study the dependence of observed\n              plasmon modes on Ga content, lending insight into plasmon\n              coupling with electron--hole excitations.",\n  journal  = "Appl. Phys. Lett.",\n  volume   =  112,\n  number   =  6,\n  pages    = "1708.03817",\n  month    =  feb,\n  year     =  2018,\n  keywords = "LeBeau Group;AFOSR",\n  issn     = "0003-6951",\n  arxivid  = "1708.03817",\n  doi      = "10.1063/1.5012742"\n}\n\n
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\n Here we demonstrate that high energy electrons can be used to explore the collective oscillation of $s$, $p$, and $d$ orbital electrons at the nanometer length scale. Using epitaxial AlGaN/AlN quantum wells as a test system, we observe the emergence of additional features in the loss spectrum with increasing Ga content. A comparison of the observed spectra with ab–initio theory reveals the origin of these spectral features is attributed to 3$d$–electrons contributed by Ga. We find that these modes differ in energy from the valence electron plasmons in Al$_\\{1-x\\}$Ga$_x$N due to the different polarizability of the $d$ electrons. Finally, we study the dependence of observed plasmon modes on Ga content, lending insight into plasmon coupling with electron–hole excitations.\n
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\n \n\n \n \n \n \n \n Numerical modeling of specimen geometry for quantitative energy dispersive X-ray spectroscopy.\n \n \n \n\n\n \n Xu, W, Dycus, J H, & LeBeau, J M\n\n\n \n\n\n\n Ultramicroscopy, 184(Pt A): 100–108. January 2018.\n \n\n\n\n
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@ARTICLE{Xu2018-rs,\n  title         = "Numerical modeling of specimen geometry for quantitative\n                   energy dispersive X-ray spectroscopy",\n  author        = "Xu, W and Dycus, J H and LeBeau, J M",\n  abstract      = "Transmission electron microscopy specimens typically exhibit\n                   local distortion at thin foil edges, which can influence the\n                   absorption of X-rays for quantitative energy dispersive\n                   X-ray spectroscopy (EDS). Here, we report a numerical,\n                   three-dimensional approach to model the geometry of general\n                   specimens and its influence on quantification when using\n                   single and multiple detector configurations. As a function\n                   of specimen tilt, we show that the model correctly predicts\n                   the asymmetric nature of X-ray counts and ratios. When using\n                   a single detector, we show that complex specimen geometries\n                   can introduce significant uncertainty in EDS quantification.\n                   Further, we show that this uncertainty can be largely\n                   negated by collection with multiple detectors placed\n                   symmetrically about the sample such as the FEI Super-X\n                   configuration. Based on guidance provided by the model, we\n                   propose methods to reduce quantification error introduced by\n                   the sample shape. The source code is available at\n                   https://github.com/subangstrom/superAngle.",\n  journal       = "Ultramicroscopy",\n  volume        =  184,\n  number        = "Pt A",\n  pages         = "100--108",\n  month         =  jan,\n  year          =  2018,\n  keywords      = "3D specimen geometry; Absorption correction; Energy\n                   dispersive X-ray spectroscopy (EDS); Error\n                   counter-balancing; Multiple EDS detectors; Super-X;LeBeau\n                   Group;AFOSR - YIP;AFOSR;Amazon",\n  copyright     = "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",\n  language      = "en",\n  archivePrefix = "arXiv",\n  eprint        = "1708.04565",\n  primaryClass  = "physics.ins-det",\n  issn          = "0304-3991, 1879-2723",\n  pmid          = "28886487",\n  arxivid       = "1708.04565",\n  doi           = "10.1016/j.ultramic.2017.08.015"\n}\n\n
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\n Transmission electron microscopy specimens typically exhibit local distortion at thin foil edges, which can influence the absorption of X-rays for quantitative energy dispersive X-ray spectroscopy (EDS). Here, we report a numerical, three-dimensional approach to model the geometry of general specimens and its influence on quantification when using single and multiple detector configurations. As a function of specimen tilt, we show that the model correctly predicts the asymmetric nature of X-ray counts and ratios. When using a single detector, we show that complex specimen geometries can introduce significant uncertainty in EDS quantification. Further, we show that this uncertainty can be largely negated by collection with multiple detectors placed symmetrically about the sample such as the FEI Super-X configuration. Based on guidance provided by the model, we propose methods to reduce quantification error introduced by the sample shape. The source code is available at https://github.com/subangstrom/superAngle.\n
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\n \n\n \n \n \n \n \n Atomic Structure of Domain and Interphase Boundaries in Ferroelectric HfO 2.\n \n \n \n\n\n \n Grimley, E. D, Schenk, T., Mikolajick, T., Schroeder, U., & LeBeau, J. M\n\n\n \n\n\n\n Advanced Materials Interfaces, 5(5): 1701258. March 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Grimley2018-je,\n  title    = "Atomic Structure of Domain and Interphase Boundaries in\n              Ferroelectric {HfO} 2",\n  author   = "Grimley, Everett D and Schenk, Tony and Mikolajick, Thomas and\n              Schroeder, Uwe and LeBeau, James M",\n  abstract = "Though the electrical responses of the various polymorphs found\n              in ferroelectric polycrystalline thin film HfO$_2$ are now well\n              characterized, little is currently understood of this novel\n              material's grain sub-structure. In particular, the formation of\n              domain and phase boundaries requires investigation to better\n              understand phase stabilization, switching, and interconversion.\n              Here, we apply scanning transmission electron microscopy to\n              investigate the atomic structure of boundaries in these\n              materials. In particular, we find orthorhombic/orthorhombic\n              domain walls and coherent orthorhombic/monoclinic interphase\n              boundaries formed throughout individual grains. The results\n              inform how interphase boundaries can impose strain conditions\n              that may be key to phase stabilization. Moreover, the atomic\n              structure near interphase boundary walls suggests potential for\n              their mobility under bias, which has been speculated to occur in\n              perovskite morphotropic phase boundary systems by mechanisms\n              similar to domain boundary motion.",\n  journal  = "Advanced Materials Interfaces",\n  volume   =  5,\n  number   =  5,\n  pages    = "1701258",\n  month    =  mar,\n  year     =  2018,\n  keywords = "LeBeau Group",\n  issn     = "2196-7350",\n  arxivid  = "1709.08110",\n  doi      = "10.1002/admi.201701258"\n}\n\n
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\n Though the electrical responses of the various polymorphs found in ferroelectric polycrystalline thin film HfO$_2$ are now well characterized, little is currently understood of this novel material's grain sub-structure. In particular, the formation of domain and phase boundaries requires investigation to better understand phase stabilization, switching, and interconversion. Here, we apply scanning transmission electron microscopy to investigate the atomic structure of boundaries in these materials. In particular, we find orthorhombic/orthorhombic domain walls and coherent orthorhombic/monoclinic interphase boundaries formed throughout individual grains. The results inform how interphase boundaries can impose strain conditions that may be key to phase stabilization. Moreover, the atomic structure near interphase boundary walls suggests potential for their mobility under bias, which has been speculated to occur in perovskite morphotropic phase boundary systems by mechanisms similar to domain boundary motion.\n
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\n \n\n \n \n \n \n \n Super Charge Separation and High Voltage Phase in Na$_{x}$MnO$_{2}$.\n \n \n \n\n\n \n Chen, X., Wang, Y., Wiaderek, K., Sang, X., Borkiewicz, O., Chapman, K., LeBeau, J. M, Lynn, J., & Li, X.\n\n\n \n\n\n\n Adv. Funct. Mater., 28(50): 1805105. December 2018.\n \n\n\n\n
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@ARTICLE{Chen2018-uu,\n  title    = "Super Charge Separation and High Voltage Phase in\n              {Na$_{x}$MnO$_{2}$}",\n  author   = "Chen, Xi and Wang, Yichao and Wiaderek, Kamila and Sang, Xiahan\n              and Borkiewicz, Olaf and Chapman, Karena and LeBeau, James M and\n              Lynn, Jeffrey and Li, Xin",\n  journal  = "Adv. Funct. Mater.",\n  volume   =  28,\n  number   =  50,\n  pages    = "1805105",\n  month    =  dec,\n  year     =  2018,\n  keywords = "LeBeau Group",\n  issn     = "1616-301X",\n  doi      = "10.1002/adfm.201805105"\n}\n\n
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\n \n\n \n \n \n \n \n Analysis of performance instabilities of Hafnia‐based ferroelectrics using modulus spectroscopy and thermally stimulated depolarization currents.\n \n \n \n\n\n \n Fengler, F. P G, Nigon, R., Muralt, P., Grimley, E. D, Sang, X., Sessi, V., Hentschel, R., LeBeau, J. M, Mikolajick, T., & Schroeder, U.\n\n\n \n\n\n\n Adv. Electron. Mater., 4(3): 1700547. March 2018.\n \n\n\n\n
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@ARTICLE{Fengler2018-yi,\n  title     = "Analysis of performance instabilities of Hafnia‐based\n               ferroelectrics using modulus spectroscopy and thermally\n               stimulated depolarization currents",\n  author    = "Fengler, Franz P G and Nigon, Robin and Muralt, Paul and\n               Grimley, Everett D and Sang, Xiahan and Sessi, Violetta and\n               Hentschel, Rico and LeBeau, James M and Mikolajick, Thomas and\n               Schroeder, Uwe",\n  abstract  = "The discovery of the ferroelectric orthorhombic phase in doped\n               hafnia films has sparked immense research efforts. Presently, a\n               major obstacle for hafnia's use in high‐endurance memory\n               applications like nonvolatile random‐access memories is its\n               unstable ferroelectric response during field cycling. Different\n               mechanisms are proposed to explain this instability including\n               field‐induced phase change, electron trapping, and oxygen\n               vacancy diffusion. However, none of these is able to fully\n               explain the complete behavior and interdependencies of these\n               phenomena. Up to now, no complete root cause for fatigue,\n               wake‐up, and imprint effects is presented. In this study, the\n               first evidence for the presence of singly and doubly positively\n               charged oxygen vacancies in hafnia--zirconia films using\n               thermally stimulated currents and impedance spectroscopy is\n               presented. Moreover, it is shown that interaction of these\n               defects with electrons at the interfaces to the electrodes may\n               cause the observed instability of the ferroelectric performance.",\n  journal   = "Adv. Electron. Mater.",\n  publisher = "Wiley",\n  volume    =  4,\n  number    =  3,\n  pages     = "1700547",\n  month     =  mar,\n  year      =  2018,\n  keywords  = "Electron trapping; Ferroelectric; Hafnium oxide; Impedance\n               spectroscopy; Oxygen vacancies; Thermally stimulated\n               depolarization current;LeBeau Group",\n  copyright = "http://onlinelibrary.wiley.com/termsAndConditions\\#vor",\n  language  = "en",\n  issn      = "2199-160X",\n  doi       = "10.1002/aelm.201700547"\n}\n\n
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\n The discovery of the ferroelectric orthorhombic phase in doped hafnia films has sparked immense research efforts. Presently, a major obstacle for hafnia's use in high‐endurance memory applications like nonvolatile random‐access memories is its unstable ferroelectric response during field cycling. Different mechanisms are proposed to explain this instability including field‐induced phase change, electron trapping, and oxygen vacancy diffusion. However, none of these is able to fully explain the complete behavior and interdependencies of these phenomena. Up to now, no complete root cause for fatigue, wake‐up, and imprint effects is presented. In this study, the first evidence for the presence of singly and doubly positively charged oxygen vacancies in hafnia–zirconia films using thermally stimulated currents and impedance spectroscopy is presented. Moreover, it is shown that interaction of these defects with electrons at the interfaces to the electrodes may cause the observed instability of the ferroelectric performance.\n
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\n \n\n \n \n \n \n \n Discovering chemical site occupancy- modulus correlations in Ni based intermetallics via statistical learning methods.\n \n \n \n\n\n \n Broderick, S. R, Kumar, A., Oni, A. A, LeBeau, J. M, Sinnott, S. B, & Rajan, K.\n\n\n \n\n\n\n Computational Condensed Matter, 14(October 2017): 8–14. 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Broderick2018-pd,\n  title     = "Discovering chemical site occupancy- modulus correlations in Ni\n               based intermetallics via statistical learning methods",\n  author    = "Broderick, Scott R and Kumar, Aakash and Oni, Adedapo A and\n               LeBeau, James M and Sinnott, Susan B and Rajan, Krishna",\n  abstract  = "We show how one may extract spectral features from the density\n               of states (DOS) of L12-Ni3Al alloys that can serve as signatures\n               or electronic ``fingerprints'' which capture the correlation\n               between site occupancy of dopants and elastic properties. Based\n               on this correlation, we have developed a computational approach\n               for rapidly identifying the impact of the selection of dopant\n               chemistries on bulk moduli of intermetallics. Our results show\n               for example that Cr preferentially occupies the Al site in Ni3Al\n               which is confirmed by scanning transmission electron microscopy\n               (STEM) energy dispersed X-ray spectroscopy (EDS) analysis. We\n               further show that this preference is due to a sensitivity of Cr\n               to the DOS at −1.7 and 0.2 eV relative to the Fermi energy. In\n               terms of similarity in chemistry-property correlations, we find\n               Cr has a similar effect to Ce when occupying an Al site, while\n               Cr occupying a Ni site has similar correlation as La on a Ni\n               site. This logic can be utilized in targeted design of new alloy\n               chemistries based on similar property correlations and for\n               targeted DOS modification.",\n  journal   = "Computational Condensed Matter",\n  publisher = "Elsevier",\n  volume    =  14,\n  number    = "October 2017",\n  pages     = "8--14",\n  year      =  2018,\n  keywords  = "Density functional theory; Density of state; Materials\n               informatics; Ni-base alloys; Scanning transmission electron\n               microscopy;LeBeau Group;AFOSR",\n  issn      = "2352-2143",\n  doi       = "10.1016/j.cocom.2017.11.001"\n}\n\n
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\n We show how one may extract spectral features from the density of states (DOS) of L12-Ni3Al alloys that can serve as signatures or electronic ``fingerprints'' which capture the correlation between site occupancy of dopants and elastic properties. Based on this correlation, we have developed a computational approach for rapidly identifying the impact of the selection of dopant chemistries on bulk moduli of intermetallics. Our results show for example that Cr preferentially occupies the Al site in Ni3Al which is confirmed by scanning transmission electron microscopy (STEM) energy dispersed X-ray spectroscopy (EDS) analysis. We further show that this preference is due to a sensitivity of Cr to the DOS at −1.7 and 0.2 eV relative to the Fermi energy. In terms of similarity in chemistry-property correlations, we find Cr has a similar effect to Ce when occupying an Al site, while Cr occupying a Ni site has similar correlation as La on a Ni site. This logic can be utilized in targeted design of new alloy chemistries based on similar property correlations and for targeted DOS modification.\n
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\n \n\n \n \n \n \n \n Structure of Ultrathin Native Oxides on III–Nitride Surfaces.\n \n \n \n\n\n \n Dycus, J H., Mirrielees, K. J, Grimley, E. D, Kirste, R., Mita, S., Sitar, Z., Collazo, R., Irving, D. L, & LeBeau, J. M\n\n\n \n\n\n\n ACS Appl. Mater. Interfaces, 10(13): 10607–10611. April 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Dycus2018-wx,\n  title    = "Structure of Ultrathin Native Oxides on {III--Nitride} Surfaces",\n  author   = "Dycus, J Houston and Mirrielees, Kelsey J and Grimley, Everett D\n              and Kirste, Ronny and Mita, Seiji and Sitar, Zlatko and Collazo,\n              Ramon and Irving, Douglas L and LeBeau, James M",\n  abstract = "When pristine material surfaces are exposed to air, highly\n              reactive broken bonds can promote the formation of surface oxides\n              with structures and properties differing greatly from bulk.\n              Determination of the oxide structure is often elusive through the\n              use of indirect diffraction methods or techniques that probe only\n              the outermost layer. As a result, surface oxides forming on\n              widely used materials, such as group III-nitrides, have not been\n              unambiguously resolved, even though critical properties can\n              depend sensitively on their presence. In this study, aberration\n              corrected scanning transmission electron microscopy reveals\n              directly, and with depth dependence, the structure of ultrathin\n              native oxides that form on AlN and GaN surfaces. Through atomic\n              resolution imaging and spectroscopy, we show that the oxide\n              layers are comprised of tetrahedra−octahedra cation−oxygen units,\n              in an arrangement similar to bulk $\\vartheta$-Al 2 O 3 and\n              $\\beta$-Ga 2 O 3 . By applying density functional theory, we show\n              that the observed structures are more stable than previously\n              proposed surface oxide models. We place the impact of these\n              observations in the context of key III-nitride growth, device\n              issues, and the recent discovery of two-dimensional nitrides.",\n  journal  = "ACS Appl. Mater. Interfaces",\n  volume   =  10,\n  number   =  13,\n  pages    = "10607--10611",\n  month    =  apr,\n  year     =  2018,\n  keywords = "aln; are the bedrock; density functional theory; further; group\n              iii nitrides; of modern solid-state lighting; roup iii nitrides;\n              scanning transmission electron microscopy; such as gan and;\n              surface reconstructions; they are of; ultrathin oxides;LeBeau\n              Group;AFOSR - YIP;AFOSR",\n  issn     = "1944-8244",\n  doi      = "10.1021/acsami.8b00845"\n}\n\n
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\n When pristine material surfaces are exposed to air, highly reactive broken bonds can promote the formation of surface oxides with structures and properties differing greatly from bulk. Determination of the oxide structure is often elusive through the use of indirect diffraction methods or techniques that probe only the outermost layer. As a result, surface oxides forming on widely used materials, such as group III-nitrides, have not been unambiguously resolved, even though critical properties can depend sensitively on their presence. In this study, aberration corrected scanning transmission electron microscopy reveals directly, and with depth dependence, the structure of ultrathin native oxides that form on AlN and GaN surfaces. Through atomic resolution imaging and spectroscopy, we show that the oxide layers are comprised of tetrahedra−octahedra cation−oxygen units, in an arrangement similar to bulk $ϑ$-Al 2 O 3 and $β$-Ga 2 O 3 . By applying density functional theory, we show that the observed structures are more stable than previously proposed surface oxide models. We place the impact of these observations in the context of key III-nitride growth, device issues, and the recent discovery of two-dimensional nitrides.\n
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\n \n\n \n \n \n \n \n Electrostatic potential and valence modulation in La0.7Sr0.3MnO3thin films.\n \n \n \n\n\n \n Trappen, R., Garcia-Castro, A C, Tra, V. T., Huang, C. Y., Ibarra-Hernandez, W., Fitch, J., Singh, S., Zhou, J., Cabrera, G., Chu, Y. H., LeBeau, J. M, Romero, A. H, & Holcomb, M. B\n\n\n \n\n\n\n Sci. Rep., 8(1): 14313. 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Trappen2018-hn,\n  title     = "Electrostatic potential and valence modulation in\n               {La0.7Sr0.3MnO3thin} films",\n  author    = "Trappen, Robbyn and Garcia-Castro, A C and Tra, Vu Thanh and\n               Huang, Chih Yeh and Ibarra-Hernandez, Wilfredo and Fitch, James\n               and Singh, Sobhit and Zhou, Jinling and Cabrera, Guerau and Chu,\n               Ying Hao and LeBeau, James M and Romero, Aldo H and Holcomb,\n               Mikel B",\n  abstract  = "The Mn valence in thin film La 0.7 Sr 0.3 MnO 3 was studied as a\n               function of film thickness in the range of 1-16 unit cells with\n               a combination of non-destructive bulk and surface sensitive\n               X-ray absorption spectroscopy techniques. Using a layer-by-layer\n               valence model, it was found that while the bulk averaged valence\n               hovers around its expected value of 3.3, a significant deviation\n               occurs within several unit cells of the surface and interface.\n               These results were supported by first principles calculations.\n               The surface valence increases to up to Mn 3.7+ , whereas the\n               interface valence reduces down to Mn 2.5+. The change in valence\n               from the expected bulk value is consistent with charge\n               redistribution due to the polar discontinuity at the\n               film-substrate interface. The comparison with theory employed\n               here illustrates how this layer-by-layer valence evolves with\n               film thickness and allows for a deeper understanding of the\n               microscopic mechanisms at play in this effect. These results\n               offer insight on how the two-dimensional electron gas is created\n               in thin film oxide alloys and how the magnetic ordering is\n               reduced with dimensionality. The family of materials known as\n               manganites has received considerable attention in the last\n               several decades as promising candidates for device applications\n               like magnetic tunnel junctions 1 and solid oxide fuel cells 2.\n               The widely-studied La 0.7 Sr 0.3 MnO 3 (LSMO) is particularly\n               appealing due to its properties such as large anisotropic\n               magnetoresistance, high spin polarization, and above room\n               temperature Curie temperature 1. However, LSMO exhibits a\n               problem that also exists in many other magnetic systems. When\n               many magnetic materials are thin, their magnetic order is lost\n               or reduced 3-5. The reduction of magnetic order can also occur\n               at the surfaces 6 and interfaces 7 of bulk materials which can\n               be problematic for some applications. The layer of reduced or\n               lost magnetism is called the magnetic dead layer. Magnetism is\n               not the only property that can change in thin films. The\n               electrical conductivity of thin film LSMO is also reduced,\n               exhibiting a temperature dependence consistent with insulators,\n               typically below a thickness of 6 unit cells (u.c.) 8,9. This\n               thickness dependent metal-to-insulator transition has been shown\n               to be a result of increased carrier scattering due to defects\n               already present in the material exacerbated by the reduced\n               dimensionality of the thin films 9. While the loss of\n               conductivity in thin films has been explained, the origin of the\n               magnetic dead layer in complex oxides is still under debate.\n               Density functional (DFT) calculations by Liao et al. show that\n               LSMO should remain magnetic even at a thickness of 1 u.c. 9\n               Studies have focused on factors such as strain 9,10 , oxygen\n               defects 9,11 , and cation non-stoichiometry 11. The influence of\n               the polar LSMO/STO interface has also been studied 12-14 ;\n               however , the implications of this effect for the electronic\n               structure of the material as well as its relation to other\n               factors that influence the dead layer are not well-established.\n               The dead layer problem restricts the development of devices that\n               utilize effects such as magnetoresistance or interfacial\n               magnetoelectricity, which require strong magnetism at the\n               material boundary or interface; thereforethere is a strong need\n               to systematically evaluate the parameter space of these\n               materials in order to learn more about the origin of the MDL and\n               how to work around it.",\n  journal   = "Sci. Rep.",\n  publisher = "Springer US",\n  volume    =  8,\n  number    =  1,\n  pages     = "14313",\n  year      =  2018,\n  keywords  = "LeBeau Group",\n  issn      = "2045-2322",\n  doi       = "10.1038/s41598-018-32701-x"\n}\n\n
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\n The Mn valence in thin film La 0.7 Sr 0.3 MnO 3 was studied as a function of film thickness in the range of 1-16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn 3.7+ , whereas the interface valence reduces down to Mn 2.5+. The change in valence from the expected bulk value is consistent with charge redistribution due to the polar discontinuity at the film-substrate interface. The comparison with theory employed here illustrates how this layer-by-layer valence evolves with film thickness and allows for a deeper understanding of the microscopic mechanisms at play in this effect. These results offer insight on how the two-dimensional electron gas is created in thin film oxide alloys and how the magnetic ordering is reduced with dimensionality. The family of materials known as manganites has received considerable attention in the last several decades as promising candidates for device applications like magnetic tunnel junctions 1 and solid oxide fuel cells 2. The widely-studied La 0.7 Sr 0.3 MnO 3 (LSMO) is particularly appealing due to its properties such as large anisotropic magnetoresistance, high spin polarization, and above room temperature Curie temperature 1. However, LSMO exhibits a problem that also exists in many other magnetic systems. When many magnetic materials are thin, their magnetic order is lost or reduced 3-5. The reduction of magnetic order can also occur at the surfaces 6 and interfaces 7 of bulk materials which can be problematic for some applications. The layer of reduced or lost magnetism is called the magnetic dead layer. Magnetism is not the only property that can change in thin films. The electrical conductivity of thin film LSMO is also reduced, exhibiting a temperature dependence consistent with insulators, typically below a thickness of 6 unit cells (u.c.) 8,9. This thickness dependent metal-to-insulator transition has been shown to be a result of increased carrier scattering due to defects already present in the material exacerbated by the reduced dimensionality of the thin films 9. While the loss of conductivity in thin films has been explained, the origin of the magnetic dead layer in complex oxides is still under debate. Density functional (DFT) calculations by Liao et al. show that LSMO should remain magnetic even at a thickness of 1 u.c. 9 Studies have focused on factors such as strain 9,10 , oxygen defects 9,11 , and cation non-stoichiometry 11. The influence of the polar LSMO/STO interface has also been studied 12-14 ; however , the implications of this effect for the electronic structure of the material as well as its relation to other factors that influence the dead layer are not well-established. The dead layer problem restricts the development of devices that utilize effects such as magnetoresistance or interfacial magnetoelectricity, which require strong magnetism at the material boundary or interface; thereforethere is a strong need to systematically evaluate the parameter space of these materials in order to learn more about the origin of the MDL and how to work around it.\n
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\n \n\n \n \n \n \n \n Charge storage mechanism and degradation of P2-type sodium transition metal oxides in aqueous electrolytes.\n \n \n \n\n\n \n Boyd, S., Dhall, R., LeBeau, J. M, & Augustyn, V.\n\n\n \n\n\n\n J. Mater. Chem. A Mater. Energy Sustain., 6(44): 22266–22276. November 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Boyd2018-fx,\n  title     = "Charge storage mechanism and degradation of P2-type sodium\n               transition metal oxides in aqueous electrolytes",\n  author    = "Boyd, Shelby and Dhall, Rohan and LeBeau, James M and Augustyn,\n               Veronica",\n  abstract  = "Few transition metal oxides exhibit sufficient stability for\n               aqueous ion intercalation from neutral pH electrolytes for\n               low-cost aqueous Na+ batteries and battery-type desalinators. P2\n               layered Na+ manganese-rich oxides have high theoretical\n               capacities and voltages for Na+ storage and are extensively\n               investigated for non-aqueous Na+ batteries. However, the charge\n               storage mechanism and factors controlling interlayer chemistry\n               and redox behavior of these materials in aqueous electrolytes\n               have not been determined. Here, we take a significant step in\n               establishing their aqueous electrochemical behavior by\n               investigating a series of P2 oxides that exhibit a range of\n               stability in water and ambient air: Na0.62Ni0.22Mn0.66Fe0.10O2\n               (NaNMFe), Na0.61Ni0.22Mn0.66Co0.10O2 (NaNMCo),\n               Na0.64Ni0.22Mn0.66Cu0.11O2 (NaNMCu), and Na0.64Mn0.62Cu0.31O2\n               (NaMCu). Depending on the transition metal composition and\n               potential, all materials exhibit significant irreversible Na+\n               loss during the first anodic cycle followed by water\n               intercalation into the interlayer. The presence of water causes\n               conversion into birnessite-like phases and microscopic\n               exfoliation of the particles. The interlayer affinity for water\n               is primarily driven by the Na+ content, which can be tuned by\n               the transition metal composition and the maximum anodic\n               potential during electrochemical cycling. The interlayer water\n               affects the reversible capacity and cycling stability of the\n               oxides, with the highest reversible capacity (∼40 mA h g−1\n               delivered in ∼30 minutes) obtained with NaNMCo. These results\n               present the first studies on the structural effects of aqueous\n               electrochemistry in P2 oxides, highlight the significant\n               differences in the electrochemical behavior of P2 oxides in\n               aqueous vs. non-aqueous electrolytes, and provide guidance on\n               how to use the transition metal chemistry to tune their aqueous\n               charge storage behavior.",\n  journal   = "J. Mater. Chem. A Mater. Energy Sustain.",\n  publisher = "The Royal Society of Chemistry",\n  volume    =  6,\n  number    =  44,\n  pages     = "22266--22276",\n  month     =  nov,\n  year      =  2018,\n  keywords  = "LeBeau Group",\n  language  = "en",\n  issn      = "2050-7488, 2050-7496",\n  doi       = "10.1039/C8TA08367C"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Few transition metal oxides exhibit sufficient stability for aqueous ion intercalation from neutral pH electrolytes for low-cost aqueous Na+ batteries and battery-type desalinators. P2 layered Na+ manganese-rich oxides have high theoretical capacities and voltages for Na+ storage and are extensively investigated for non-aqueous Na+ batteries. However, the charge storage mechanism and factors controlling interlayer chemistry and redox behavior of these materials in aqueous electrolytes have not been determined. Here, we take a significant step in establishing their aqueous electrochemical behavior by investigating a series of P2 oxides that exhibit a range of stability in water and ambient air: Na0.62Ni0.22Mn0.66Fe0.10O2 (NaNMFe), Na0.61Ni0.22Mn0.66Co0.10O2 (NaNMCo), Na0.64Ni0.22Mn0.66Cu0.11O2 (NaNMCu), and Na0.64Mn0.62Cu0.31O2 (NaMCu). Depending on the transition metal composition and potential, all materials exhibit significant irreversible Na+ loss during the first anodic cycle followed by water intercalation into the interlayer. The presence of water causes conversion into birnessite-like phases and microscopic exfoliation of the particles. The interlayer affinity for water is primarily driven by the Na+ content, which can be tuned by the transition metal composition and the maximum anodic potential during electrochemical cycling. The interlayer water affects the reversible capacity and cycling stability of the oxides, with the highest reversible capacity (∼40 mA h g−1 delivered in ∼30 minutes) obtained with NaNMCo. These results present the first studies on the structural effects of aqueous electrochemistry in P2 oxides, highlight the significant differences in the electrochemical behavior of P2 oxides in aqueous vs. non-aqueous electrolytes, and provide guidance on how to use the transition metal chemistry to tune their aqueous charge storage behavior.\n
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\n \n\n \n \n \n \n \n Gradient chemical order in the relaxor Pb(Mg$_{1∕3}$Nb$_{2/3}$)O$_{3}$.\n \n \n \n\n\n \n Cabral, M. J, Zhang, S., Dickey, E. C, & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 112(8): 082901. February 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Cabral2018-dp,\n  title    = "Gradient chemical order in the relaxor\n              {Pb(Mg$_{1∕3}$Nb$_{2/3}$)O$_{3}$}",\n  author   = "Cabral, Matthew J and Zhang, Shujun and Dickey, Elizabeth C and\n              LeBeau, James M",\n  journal  = "Appl. Phys. Lett.",\n  volume   =  112,\n  number   =  8,\n  pages    = "082901",\n  month    =  feb,\n  year     =  2018,\n  keywords = "LeBeau Group",\n  issn     = "0003-6951",\n  doi      = "10.1063/1.5016561"\n}\n\n
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\n \n\n \n \n \n \n \n Complexities of atomic structure at CdO/MgO and CdO/Al$_{2}$O$_{3}$ interfaces.\n \n \n \n\n\n \n Grimley, E. D, Wynn, A. P, Kelley, K. P, Sachet, E., Dean, J. S, Freeman, C. L, Maria, J., & LeBeau, J. M\n\n\n \n\n\n\n J. Appl. Phys., 124(20): 205302. November 2018.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Grimley2018-zh,\n  title     = "Complexities of atomic structure at {CdO/MgO} and\n               {CdO/Al$_{2}$O$_{3}$} interfaces",\n  author    = "Grimley, Everett D and Wynn, Alex P and Kelley, Kyle P and\n               Sachet, Edward and Dean, Julian S and Freeman, Colin L and\n               Maria, Jon-Paul and LeBeau, James M",\n  abstract  = "We report the interface structures of CdO thin films on 001-MgO\n               and 0001-Al 2O 3 substrates. Using aberration corrected scanning\n               transmission electron microscopy, we show that epitaxial growth\n               of (001)-CdO ?(001)-MgO occurs with a lattice misfit greater\n               than 10\\%. A high density of interface misfit dislocations is\n               found to form. In combination with molecular dynamics\n               simulations, we show that dislocation strain fields form and\n               overlap in very thin heterostructures of CdO and MgO ( <3?nm).\n               On the c-Al 2O 3 substrate, we find that CdO grows with a\n               surface normal of 025. We show that three rotation variants form\n               due to the symmetry of the sapphire surface. These results\n               contribute insights into the epitaxial growth of these rock-salt\n               oxides.",\n  journal   = "J. Appl. Phys.",\n  publisher = "American Institute of Physics",\n  volume    =  124,\n  number    =  20,\n  pages     = "205302",\n  month     =  nov,\n  year      =  2018,\n  keywords  = "LeBeau Group",\n  issn      = "0021-8979",\n  doi       = "10.1063/1.5053752"\n}\n\n
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\n We report the interface structures of CdO thin films on 001-MgO and 0001-Al 2O 3 substrates. Using aberration corrected scanning transmission electron microscopy, we show that epitaxial growth of (001)-CdO ?(001)-MgO occurs with a lattice misfit greater than 10%. A high density of interface misfit dislocations is found to form. In combination with molecular dynamics simulations, we show that dislocation strain fields form and overlap in very thin heterostructures of CdO and MgO ( <3?nm). On the c-Al 2O 3 substrate, we find that CdO grows with a surface normal of 025. We show that three rotation variants form due to the symmetry of the sapphire surface. These results contribute insights into the epitaxial growth of these rock-salt oxides.\n
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\n \n\n \n \n \n \n \n 6 kW/cm$^2$ UVC laser threshold in optically pumped lasers achieved by controlling point defect formation.\n \n \n \n\n\n \n Kirste, R., Guo, Q., Dycus, J H., Franke, A., Mita, S., Sarkar, B., Reddy, P., LeBeau, J. M, Collazo, R., & Sitar, Z.\n\n\n \n\n\n\n Appl. Phys. Express, 11(8): 082101. 2018.\n \n\n\n\n
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@ARTICLE{Kirste2018-mh,\n  title    = "6 {kW/cm$^2$} {UVC} laser threshold in optically pumped lasers\n              achieved by controlling point defect formation",\n  author   = "Kirste, Ronny and Guo, Qiang and Dycus, J Houston and Franke,\n              Alexander and Mita, Seiji and Sarkar, Biplab and Reddy, Pramod\n              and LeBeau, James M and Collazo, Ramon and Sitar, Zlatko",\n  journal  = "Appl. Phys. Express",\n  volume   =  11,\n  number   =  8,\n  pages    = "082101",\n  year     =  2018,\n  keywords = "LeBeau Group",\n  issn     = "1882-0778",\n  doi      = "10.7567/APEX.11.082101"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n \n\n \n \n \n \n \n Si doped hafnium oxide - A ``fragile'' ferroelectric system.\n \n \n \n\n\n \n Richter, C., Schenk, T., Park, M. H., Tscharntke, F. A, Grimley, E. D, LeBeau, J. M, Zhou, C., Fancher, C. M, Jones, J. L, Mikolajick, T., & Schroeder, U.\n\n\n \n\n\n\n Advanced Electronic Materials, 3(10): 1700131. October 2017.\n \n\n\n\n
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@ARTICLE{Richter2017-ho,\n  title    = "Si doped hafnium oxide - A ``fragile'' ferroelectric system",\n  author   = "Richter, Claudia and Schenk, Tony and Park, Min Hyuk and\n              Tscharntke, Franziska A and Grimley, Everett D and LeBeau, James\n              M and Zhou, Chuanzhen and Fancher, Chris M and Jones, Jacob L and\n              Mikolajick, Thomas and Schroeder, Uwe",\n  journal  = "Advanced Electronic Materials",\n  volume   =  3,\n  number   =  10,\n  pages    = "1700131",\n  month    =  oct,\n  year     =  2017,\n  keywords = "Landau theory; Rietveld analysis; ferroelectrics; hafnium\n              oxide;LeBeau Group",\n  issn     = "2199-160X",\n  doi      = "10.1002/aelm.201700131"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n \n\n \n \n \n \n \n Transition from Battery to Pseudocapacitor Behavior via Structural Water in Tungsten Oxide.\n \n \n \n\n\n \n Mitchell, J. B, Lo, W. C, Genc, A., LeBeau, J. M, & Augustyn, V.\n\n\n \n\n\n\n Chem. Mater., 29(9): 3928–3937. May 2017.\n \n\n\n\n
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@ARTICLE{Mitchell2017-ga,\n  title     = "Transition from Battery to Pseudocapacitor Behavior via\n               Structural Water in Tungsten Oxide",\n  author    = "Mitchell, James B and Lo, William C and Genc, Arda and LeBeau,\n               James M and Augustyn, Veronica",\n  abstract  = "The kinetics of energy storage in transition metal oxides are\n               usually limited by solid-state diffusion, and the strategy most\n               often utilized to improve their rate capability is to reduce ion\n               diffusion distances by utilizing nanostructured materials. Here,\n               another strategy for …",\n  journal   = "Chem. Mater.",\n  publisher = "ACS Publications",\n  volume    =  29,\n  number    =  9,\n  pages     = "3928--3937",\n  month     =  may,\n  year      =  2017,\n  keywords  = "LeBeau Group",\n  issn      = "0897-4756",\n  doi       = "10.1021/acs.chemmater.6b05485"\n}\n\n
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\n The kinetics of energy storage in transition metal oxides are usually limited by solid-state diffusion, and the strategy most often utilized to improve their rate capability is to reduce ion diffusion distances by utilizing nanostructured materials. Here, another strategy for …\n
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\n \n\n \n \n \n \n \n An Ultrathin Single Crystalline Relaxor Ferroelectric Integrated on a High Mobility Semiconductor.\n \n \n \n\n\n \n Moghadam, R. M, Xiao, Z., Ahmadi-Majlan, K., Grimley, E. D, Bowden, M., Ong, P., Chambers, S. A, LeBeau, J. M, Hong, X., Sushko, P. V, & Ngai, J. H\n\n\n \n\n\n\n Nano Lett., 17(10): 6248–6257. October 2017.\n \n\n\n\n
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@ARTICLE{Moghadam2017-pe,\n  title    = "An Ultrathin Single Crystalline Relaxor Ferroelectric Integrated\n              on a High Mobility Semiconductor",\n  author   = "Moghadam, Reza M and Xiao, Zhiyong and Ahmadi-Majlan, Kamyar and\n              Grimley, Everett D and Bowden, Mark and Ong, Phuong-Vu and\n              Chambers, Scott A and LeBeau, James M and Hong, Xia and Sushko,\n              Peter V and Ngai, Joseph H",\n  abstract = "\\copyright{} 2017 American Chemical Society. The epitaxial growth\n              of multifunctional oxides on semiconductors has opened a pathway\n              to introduce new functionalities to semiconductor device\n              technologies. In particular, the integration of gate materials\n              that enable nonvolatile or hysteretic functionality in\n              field-effect transistors could lead to device technologies that\n              consume less power or allow for novel modalities in computing.\n              Here we present electrical characterization of ultrathin single\n              crystalline SrZr x Ti 1-x O 3 (x = 0.7) films epitaxially grown\n              on a high mobility semiconductor, Ge. Epitaxial films of SrZr x\n              Ti 1-x O 3 exhibit relaxor behavior, characterized by a\n              hysteretic polarization that can modulate the surface potential\n              of Ge. We find that gate layers as thin as 5 nm corresponding to\n              an equivalent-oxide thickness of just 1.0 nm exhibit a ∼2 V\n              hysteretic window in the capacitance-voltage characteristics. The\n              development of hysteretic metal-oxide-semiconductor capacitors\n              with nanoscale gate thicknesses opens new vistas for\n              nanoelectronic devices.",\n  journal  = "Nano Lett.",\n  volume   =  17,\n  number   =  10,\n  pages    = "6248--6257",\n  month    =  oct,\n  year     =  2017,\n  keywords = "Crystalline oxides on semiconductors; a materials platform for; a\n              variety of; crystalline oxides on semiconductors; erroelectrics\n              integrated on semiconductors; have long been; metal;\n              metal-oxide-semiconductor capacitors; multifunctional oxides;\n              oxide; proposed to serve as; relaxor ferroelectrics;\n              semiconductor capacitors;LeBeau Group",\n  issn     = "1530-6984",\n  doi      = "10.1021/acs.nanolett.7b02947"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n © 2017 American Chemical Society. The epitaxial growth of multifunctional oxides on semiconductors has opened a pathway to introduce new functionalities to semiconductor device technologies. In particular, the integration of gate materials that enable nonvolatile or hysteretic functionality in field-effect transistors could lead to device technologies that consume less power or allow for novel modalities in computing. Here we present electrical characterization of ultrathin single crystalline SrZr x Ti 1-x O 3 (x = 0.7) films epitaxially grown on a high mobility semiconductor, Ge. Epitaxial films of SrZr x Ti 1-x O 3 exhibit relaxor behavior, characterized by a hysteretic polarization that can modulate the surface potential of Ge. We find that gate layers as thin as 5 nm corresponding to an equivalent-oxide thickness of just 1.0 nm exhibit a ∼2 V hysteretic window in the capacitance-voltage characteristics. The development of hysteretic metal-oxide-semiconductor capacitors with nanoscale gate thicknesses opens new vistas for nanoelectronic devices.\n
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\n \n\n \n \n \n \n \n Highly tensile-strained Ge/InAlAs nanocomposites.\n \n \n \n\n\n \n Jung, D., Faucher, J., Mukherjee, S., Akey, A., Ironside, D. J D J, Cabral, M., Sang, X., LeBeau, J. M, Bank, S R S. R, Buonassisi, T., Moutanabbir, O., & Lee, M. L. M L\n\n\n \n\n\n\n Nat. Commun., 8: 14204. January 2017.\n \n\n\n\n
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@ARTICLE{Jung2017-oo,\n  title     = "Highly tensile-strained {Ge/InAlAs} nanocomposites",\n  author    = "Jung, Daehwan and Faucher, Joseph and Mukherjee, Samik and Akey,\n               Austin and Ironside, Daniel J D J and Cabral, Matthew and Sang,\n               Xiahan and LeBeau, James M and Bank, S R Seth R and Buonassisi,\n               Tonio and Moutanabbir, Oussama and Lee, Minjoo Larry M L",\n  abstract  = "\\copyright{} The Author(s) 2017. Self-assembled nanocomposites\n               have been extensively investigated due to the novel properties\n               that can emerge when multiple material phases are combined.\n               Growth of epitaxial nanocomposites using lattice-mismatched\n               constituents also enables strain-engineering, which can be used\n               to further enhance material properties. Here, we report\n               self-assembled growth of highly tensile-strained Ge/In 0.52 Al\n               0.48 As (InAlAs) nanocomposites by using spontaneous phase\n               separation. Transmission electron microscopy shows a high\n               density of single-crystalline germanium nanostructures\n               coherently embedded in InAlAs without extended defects, and\n               Raman spectroscopy reveals a 3.8\\% biaxial tensile strain in the\n               germanium nanostructures. We also show that the strain in the\n               germanium nanostructures can be tuned to 5.3\\% by altering the\n               lattice constant of the matrix material, illustrating the\n               versatility of epitaxial nanocomposites for strain engineering.\n               Photoluminescence and electroluminescence results are then\n               discussed to illustrate the potential for realizing devices\n               based on this nanocomposite material.",\n  journal   = "Nat. Commun.",\n  publisher = "Nature Publishing Group",\n  volume    =  8,\n  pages     = "14204",\n  month     =  jan,\n  year      =  2017,\n  keywords  = "LeBeau Group",\n  issn      = "2041-1723",\n  doi       = "10.1038/ncomms14204"\n}\n\n
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\n © The Author(s) 2017. Self-assembled nanocomposites have been extensively investigated due to the novel properties that can emerge when multiple material phases are combined. Growth of epitaxial nanocomposites using lattice-mismatched constituents also enables strain-engineering, which can be used to further enhance material properties. Here, we report self-assembled growth of highly tensile-strained Ge/In 0.52 Al 0.48 As (InAlAs) nanocomposites by using spontaneous phase separation. Transmission electron microscopy shows a high density of single-crystalline germanium nanostructures coherently embedded in InAlAs without extended defects, and Raman spectroscopy reveals a 3.8% biaxial tensile strain in the germanium nanostructures. We also show that the strain in the germanium nanostructures can be tuned to 5.3% by altering the lattice constant of the matrix material, illustrating the versatility of epitaxial nanocomposites for strain engineering. Photoluminescence and electroluminescence results are then discussed to illustrate the potential for realizing devices based on this nanocomposite material.\n
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\n \n\n \n \n \n \n \n A comprehensive study on the structural evolution of HfO$_2$ thin films doped with various dopants.\n \n \n \n\n\n \n Park, M. H., Schenk, T., Fancher, C. M, Grimley, E. D, Zhou, C., Richter, C., LeBeau, J. M, Jones, J. L, Mikolajick, T., & Schroeder, U.\n\n\n \n\n\n\n J. Mater. Chem., 5(19): 4677–4690. 2017.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Park2017-jw,\n  title    = "A comprehensive study on the structural evolution of {HfO$_2$}\n              thin films doped with various dopants",\n  author   = "Park, Min Hyuk and Schenk, Tony and Fancher, Chris M and Grimley,\n              Everett D and Zhou, Chuanzhen and Richter, Claudia and LeBeau,\n              James M and Jones, Jacob L and Mikolajick, Thomas and Schroeder,\n              Uwe",\n  abstract = "Quantitative phase analysis is first performed on doped Hafnia\n              films to elucidate the structural origin of unexpected\n              ferroelectricity.",\n  journal  = "J. Mater. Chem.",\n  volume   =  5,\n  number   =  19,\n  pages    = "4677--4690",\n  year     =  2017,\n  keywords = "LeBeau Group",\n  issn     = "0959-9428, 2050-7526",\n  doi      = "10.1039/C7TC01200D"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Quantitative phase analysis is first performed on doped Hafnia films to elucidate the structural origin of unexpected ferroelectricity.\n
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\n \n\n \n \n \n \n \n Structural and electrical properties of single crystalline SrZrO$_3$ epitaxially grown on Ge (001).\n \n \n \n\n\n \n Lim, Z H, Ahmadi-Majlan, K, Grimley, E D, Du, Y, Bowden, M, Moghadam, R, LeBeau, J M, Chambers, S A, & Ngai, J H\n\n\n \n\n\n\n J. Appl. Phys., 122(8): 084102. August 2017.\n \n\n\n\n
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@ARTICLE{Lim2017-ze,\n  title    = "Structural and electrical properties of single crystalline\n              {SrZrO$_3$} epitaxially grown on {Ge} (001)",\n  author   = "Lim, Z H and Ahmadi-Majlan, K and Grimley, E D and Du, Y and\n              Bowden, M and Moghadam, R and LeBeau, J M and Chambers, S A and\n              Ngai, J H",\n  abstract = "\\copyright{} 2017 Author(s). We present structural and electrical\n              characterization of SrZrO 3 that has been epitaxially grown on\n              Ge(001) by oxide molecular beam epitaxy. Single crystalline SrZrO\n              3 can be nucleated on Ge via deposition at low temperatures\n              followed by annealing at 550 °C in ultra-high vacuum.\n              Photoemission spectroscopy measurements reveal that SrZrO 3\n              exhibits a type-I band arrangement with respect to Ge, with\n              conduction and valence band offsets of 1.4 eV and 3.66 eV,\n              respectively. Capacitance-voltage and current-voltage\n              measurements on 4 nm thick films reveal low leakage current\n              densities and an unpinned Fermi level at the interface that\n              allows modulation of the surface potential of Ge. Ultra-thin\n              films of epitaxial SrZrO 3 can thus be explored as a potential\n              gate dielectric for Ge.",\n  journal  = "J. Appl. Phys.",\n  volume   =  122,\n  number   =  8,\n  pages    = "084102",\n  month    =  aug,\n  year     =  2017,\n  keywords = "LeBeau Group",\n  issn     = "0021-8979",\n  doi      = "10.1063/1.5000142"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n © 2017 Author(s). We present structural and electrical characterization of SrZrO 3 that has been epitaxially grown on Ge(001) by oxide molecular beam epitaxy. Single crystalline SrZrO 3 can be nucleated on Ge via deposition at low temperatures followed by annealing at 550 °C in ultra-high vacuum. Photoemission spectroscopy measurements reveal that SrZrO 3 exhibits a type-I band arrangement with respect to Ge, with conduction and valence band offsets of 1.4 eV and 3.66 eV, respectively. Capacitance-voltage and current-voltage measurements on 4 nm thick films reveal low leakage current densities and an unpinned Fermi level at the interface that allows modulation of the surface potential of Ge. Ultra-thin films of epitaxial SrZrO 3 can thus be explored as a potential gate dielectric for Ge.\n
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\n \n\n \n \n \n \n \n The role of ceramic and glass science research in meeting societal challenges: Report from an NSF ‐sponsored workshop.\n \n \n \n\n\n \n Faber, K. T, Asefa, T., Backhaus-Ricoult, M., Brow, R., Chan, J. Y, Dillon, S., Fahrenholtz, W. G, Finnis, M. W, Garay, J. E, Garcı́a, R Edwin, Gogotsi, Y., Haile, S. M, Halloran, J., Hu, J., Huang, L., Jacobsen, S. D, Lara-Curzio, E., LeBeau, J. M, Lee, W. E, Levi, C. G, Levin, I., Lewis, J. A, Lipkin, D. M, Lu, K., Luo, J., Maria, J., Martin, L. W, Martin, S., Messing, G., Navrotsky, A., Padture, N. P, Randall, C., Rohrer, G. S, Rosenflanz, A., Schaedler, T. A, Schlom, D. G, Sehirlioglu, A., Stevenson, A. J, Tani, T., Tikare, V., Trolier-McKinstry, S., Wang, H., & Yildiz, B.\n\n\n \n\n\n\n J. Am. Ceram. Soc., 100(5): 1777–1803. May 2017.\n \n\n\n\n
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@ARTICLE{Faber2017-kp,\n  title     = "The role of ceramic and glass science research in meeting\n               societal challenges: Report from an {NSF} ‐sponsored workshop",\n  author    = "Faber, Katherine T and Asefa, Tewodros and Backhaus-Ricoult,\n               Monika and Brow, Richard and Chan, Julia Y and Dillon, Shen and\n               Fahrenholtz, William G and Finnis, Michael W and Garay, Javier E\n               and Garc{\\'\\i}a, R Edwin and Gogotsi, Yury and Haile, Sossina M\n               and Halloran, John and Hu, Juejun and Huang, Liping and\n               Jacobsen, Steven D and Lara-Curzio, Edgar and LeBeau, James M\n               and Lee, William E and Levi, Carlos G and Levin, Igor and Lewis,\n               Jennifer A and Lipkin, Don M and Lu, Kathy and Luo, Jian and\n               Maria, Jon-Paul and Martin, Lane W and Martin, Steve and\n               Messing, Gary and Navrotsky, Alexandra and Padture, Nitin P and\n               Randall, Clive and Rohrer, Gregory S and Rosenflanz, Anatoly and\n               Schaedler, Tobias A and Schlom, Darrell G and Sehirlioglu, Alp\n               and Stevenson, Adam J and Tani, Toshihiko and Tikare, Veena and\n               Trolier-McKinstry, Susan and Wang, Hong and Yildiz, Bilge",\n  abstract  = "Under the sponsorship of the U.S. National Science Foundation, a\n               workshop on emerging research opportunities in ceramic and glass\n               science was held in September 2016. Reported here are\n               proceedings of the workshop. The report details eight challenges\n               identified through workshop discussions: Ceramic processing:\n               Programmable design and assembly; The defect genome:\n               Understanding, characterizing, and predicting defects across\n               time and length scales; Functionalizing defects for\n               unprecedented properties; Ceramic flatlands: Defining\n               structure-property relations in free-standing, supported, and\n               confined two-dimensional ceramics; Ceramics in the extreme:\n               Discovery and design strategies; Ceramics in the extreme:\n               Behavior of multimaterial systems; Understanding and exploiting\n               glasses and melts under extreme conditions; and Rational design\n               of functional glasses guided by predictive modeling. It is\n               anticipated that these challenges, once met, will promote basic\n               understanding and ultimately enable advancements within multiple\n               sectors, including energy, environment, manufacturing, security,\n               and health care.",\n  journal   = "J. Am. Ceram. Soc.",\n  publisher = "Wiley",\n  volume    =  100,\n  number    =  5,\n  pages     = "1777--1803",\n  month     =  may,\n  year      =  2017,\n  keywords  = "defects; glass; layered ceramics; processing;\n               ultrahigh-temperature ceramics;LeBeau Group",\n  copyright = "http://creativecommons.org/licenses/by/4.0/",\n  language  = "en",\n  issn      = "0002-7820, 1551-2916",\n  doi       = "10.1111/jace.14881"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Under the sponsorship of the U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held in September 2016. Reported here are proceedings of the workshop. The report details eight challenges identified through workshop discussions: Ceramic processing: Programmable design and assembly; The defect genome: Understanding, characterizing, and predicting defects across time and length scales; Functionalizing defects for unprecedented properties; Ceramic flatlands: Defining structure-property relations in free-standing, supported, and confined two-dimensional ceramics; Ceramics in the extreme: Discovery and design strategies; Ceramics in the extreme: Behavior of multimaterial systems; Understanding and exploiting glasses and melts under extreme conditions; and Rational design of functional glasses guided by predictive modeling. It is anticipated that these challenges, once met, will promote basic understanding and ultimately enable advancements within multiple sectors, including energy, environment, manufacturing, security, and health care.\n
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\n \n\n \n \n \n \n \n A reliable approach to prepare brittle semiconducting materials for cross-sectional transmission electron microscopy.\n \n \n \n\n\n \n Dycus, J H, & LeBeau, J M\n\n\n \n\n\n\n J. Microsc., 268(3): 225–229. December 2017.\n \n\n\n\n
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@ARTICLE{Dycus2017-cb,\n  title    = "A reliable approach to prepare brittle semiconducting materials\n              for cross-sectional transmission electron microscopy",\n  author   = "Dycus, J H and LeBeau, J M",\n  abstract = "Here, we present a sample preparation approach that simplifies\n              the thinning of very brittle wide bandgap semiconducting\n              materials in cross-section geometry for (scanning) transmission\n              electron microscopy. Using AlN thin films grown on sapphire and\n              AlN substrates as case studies, we demonstrate that high-quality\n              samples can be routinely prepared while greatly reducing the\n              preparation time and consumables cost. The approach removes the\n              sample preparation barrier to studying a wide variety of\n              materials by electron microscopy.",\n  journal  = "J. Microsc.",\n  volume   =  268,\n  number   =  3,\n  pages    = "225--229",\n  month    =  dec,\n  year     =  2017,\n  keywords = "Cross-sectioning; Ion milling; STEM; Sample preparation; TEM;\n              Wedge polishing;LeBeau Group;AFOSR - YIP;AFOSR",\n  language = "en",\n  issn     = "0022-2720, 1365-2818",\n  pmid     = "28686283",\n  doi      = "10.1111/jmi.12601"\n}\n\n
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\n Here, we present a sample preparation approach that simplifies the thinning of very brittle wide bandgap semiconducting materials in cross-section geometry for (scanning) transmission electron microscopy. Using AlN thin films grown on sapphire and AlN substrates as case studies, we demonstrate that high-quality samples can be routinely prepared while greatly reducing the preparation time and consumables cost. The approach removes the sample preparation barrier to studying a wide variety of materials by electron microscopy.\n
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\n \n\n \n \n \n \n \n In-situ real-space imaging of single crystal surface reconstructions via electron microscopy.\n \n \n \n\n\n \n Xu, W., Bowes, P. C, Grimley, E. D, Irving, D. L, & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 109(20): 201601. November 2016.\n \n\n\n\n
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@ARTICLE{Xu2016-nf,\n  title    = "In-situ real-space imaging of single crystal surface\n              reconstructions via electron microscopy",\n  author   = "Xu, Weizong and Bowes, Preston C and Grimley, Everett D and\n              Irving, Douglas L and LeBeau, James M",\n  abstract = "Crystal surfaces are sensitive to the surrounding environment,\n              where atoms left with broken bonds reconstruct to minimize\n              surface energy. In many cases, the surface can exhibit chemical\n              properties unique from the bulk. These differences are important\n              as they control reactions and mediate thin film growth. This is\n              particularly true for complex oxides where certain terminating\n              crystal planes are polar and have a net dipole moment. For polar\n              terminations, reconstruction of atoms on the surface is the\n              central mechanism to avoid the so called polar catastrophe. This\n              adds to the complexity of the reconstruction where charge\n              polarization and stoichiometry govern the final surface in\n              addition to standard thermodynamic parameters such as temperature\n              and partial pressure. Here we present direct, in-situ\n              determination of polar SrTiO3 (110) surfaces at temperatures up\n              to 900 C using cross-sectional aberration corrected scanning\n              transmission electron microscopy (STEM). Under these conditions,\n              we observe the coexistence of various surface structures that\n              change as a function of temperature. As the specimen temperature\n              is lowered, the reconstructed surface evolves due to thermal\n              mismatch with the substrate. Periodic defects, similar to\n              dislocations, are found in these surface structures and act to\n              relieve stress due to mismatch. Combining STEM observations and\n              electron spectroscopy with density functional theory, we find a\n              combination of lattice misfit and charge compensation for\n              stabilization. Beyond the characterization of these complex\n              reconstructions, we have developed a general framework that opens\n              a new pathway to simultaneously investigate the surface and near\n              surface regions of single crystals as a function of environment.",\n  journal  = "Appl. Phys. Lett.",\n  volume   =  109,\n  number   =  20,\n  pages    = "201601",\n  month    =  nov,\n  year     =  2016,\n  keywords = "LeBeau Group",\n  issn     = "0003-6951",\n  arxivid  = "1606.01224",\n  doi      = "10.1063/1.4967978"\n}\n\n
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\n Crystal surfaces are sensitive to the surrounding environment, where atoms left with broken bonds reconstruct to minimize surface energy. In many cases, the surface can exhibit chemical properties unique from the bulk. These differences are important as they control reactions and mediate thin film growth. This is particularly true for complex oxides where certain terminating crystal planes are polar and have a net dipole moment. For polar terminations, reconstruction of atoms on the surface is the central mechanism to avoid the so called polar catastrophe. This adds to the complexity of the reconstruction where charge polarization and stoichiometry govern the final surface in addition to standard thermodynamic parameters such as temperature and partial pressure. Here we present direct, in-situ determination of polar SrTiO3 (110) surfaces at temperatures up to 900 C using cross-sectional aberration corrected scanning transmission electron microscopy (STEM). Under these conditions, we observe the coexistence of various surface structures that change as a function of temperature. As the specimen temperature is lowered, the reconstructed surface evolves due to thermal mismatch with the substrate. Periodic defects, similar to dislocations, are found in these surface structures and act to relieve stress due to mismatch. Combining STEM observations and electron spectroscopy with density functional theory, we find a combination of lattice misfit and charge compensation for stabilization. Beyond the characterization of these complex reconstructions, we have developed a general framework that opens a new pathway to simultaneously investigate the surface and near surface regions of single crystals as a function of environment.\n
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\n \n\n \n \n \n \n \n Physical Mechanisms behind the Field-Cycling Behavior of HfO$_{2}$-Based Ferroelectric Capacitors.\n \n \n \n\n\n \n Pe ̌sić, M., Fengler, F. P. G., Larcher, L., Padovani, A., Schenk, T., Grimley, E. D, Sang, X., LeBeau, J. M, Slesazeck, S., Schroeder, U., & Mikolajick, T.\n\n\n \n\n\n\n Adv. Funct. Mater., 26(25): 4601–4612. July 2016.\n \n\n\n\n
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@ARTICLE{Pesic2016-pa,\n  title    = "Physical Mechanisms behind the {Field-Cycling} Behavior of\n              {HfO$_{2}$-Based} Ferroelectric Capacitors",\n  author   = "Pe{\\v s}i{\\'c}, Milan and Fengler, Franz Paul Gustav and Larcher,\n              Luca and Padovani, Andrea and Schenk, Tony and Grimley, Everett D\n              and Sang, Xiahan and LeBeau, James M and Slesazeck, Stefan and\n              Schroeder, Uwe and Mikolajick, Thomas",\n  abstract = "Novel hafnium oxide (HfO2)-based ferroelectrics reveal full\n              scalability and complementary metal oxide semiconductor\n              integratability compared to perovskite-based ferroelectrics that\n              are currently used in nonvolatile ferroelectric random access\n              memories (FeRAMs). Within the lifetime of the device, two main\n              regimes of wake-up and fatigue can be identified. Up to now, the\n              mechanisms behind these two device stages have not been revealed.\n              Thus, the main scope of this study is an identification of the\n              root cause for the increase of the remnant polarization during\n              the wake-up phase and subsequent polarization degradation with\n              further cycling. Combining the comprehensive ferroelectric\n              switching current experiments, Preisach density analysis, and\n              transmission electron microscopy (TEM) study with compact and\n              Technology Computer Aided Design (TCAD) modeling, it has been\n              found out that during the wake-up of the device no new defects\n              are generated but the existing defects redistribute within the\n              device. Furthermore, vacancy diffusion has been identified as the\n              main cause for the phase transformation and consequent increase\n              of the remnant polarization. Utilizing trap density spectroscopy\n              for examining defect evolution with cycling of the device\n              together with modeling of the degradation results in an\n              understanding of the main mechanisms behind the evolution of the\n              ferroelectric response.",\n  journal  = "Adv. Funct. Mater.",\n  volume   =  26,\n  number   =  25,\n  pages    = "4601--4612",\n  month    =  jul,\n  year     =  2016,\n  keywords = "FeCAP; Modeling; ferroelectric HfO2; phase-change;LeBeau\n              Group;HfO2",\n  issn     = "1616-301X, 1616-3028",\n  doi      = "10.1002/adfm.201600590"\n}\n\n
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\n Novel hafnium oxide (HfO2)-based ferroelectrics reveal full scalability and complementary metal oxide semiconductor integratability compared to perovskite-based ferroelectrics that are currently used in nonvolatile ferroelectric random access memories (FeRAMs). Within the lifetime of the device, two main regimes of wake-up and fatigue can be identified. Up to now, the mechanisms behind these two device stages have not been revealed. Thus, the main scope of this study is an identification of the root cause for the increase of the remnant polarization during the wake-up phase and subsequent polarization degradation with further cycling. Combining the comprehensive ferroelectric switching current experiments, Preisach density analysis, and transmission electron microscopy (TEM) study with compact and Technology Computer Aided Design (TCAD) modeling, it has been found out that during the wake-up of the device no new defects are generated but the existing defects redistribute within the device. Furthermore, vacancy diffusion has been identified as the main cause for the phase transformation and consequent increase of the remnant polarization. Utilizing trap density spectroscopy for examining defect evolution with cycling of the device together with modeling of the degradation results in an understanding of the main mechanisms behind the evolution of the ferroelectric response.\n
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\n \n\n \n \n \n \n \n Unleashing strain induced ferroelectricity in complex oxide thin films via precise stoichiometry control.\n \n \n \n\n\n \n Haislmaier, R. C R C, Grimley, E. D E D, Biegalski, M D M. D, LeBeau, J. M, Trolier-McKinstry, S., Gopalan, V., & Engel-Herbert, R.\n\n\n \n\n\n\n Adv. Funct. Mater., 26(40): 7271–7279. October 2016.\n \n\n\n\n
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@ARTICLE{Haislmaier2016-kj,\n  title    = "Unleashing strain induced ferroelectricity in complex oxide thin\n              films via precise stoichiometry control",\n  author   = "Haislmaier, Ryan C R C and Grimley, Everett D E D and Biegalski,\n              M D Michael D and LeBeau, James M and Trolier-McKinstry, Susan\n              and Gopalan, Venkatraman and Engel-Herbert, Roman",\n  abstract = "\\copyright{} 2016 WILEY-VCH Verlag GmbH \\& Co. KGaA, Weinheim\n              Strain tuning has emerged as a powerful means to enhance\n              properties and to induce otherwise unattainable phenomena in\n              complex oxide films. However, by employing strain alone, the\n              predicted properties sometimes fail to emerge. In this work, the\n              critical role of precise stoichiometry control for realizing\n              strain-induced ferroelectricity in CaTiO 3 films is demonstrated.\n              An adsorption controlled growth window is discovered for CaTiO 3\n              films grown by hybrid molecular beam epitaxy, which ensures an\n              excellent control over the Ti:Ca atomic percent ratio of < 0.8\\%\n              in the films. Superior ferroelectric and dielectric properties\n              are found for films grown inside the stoichiometric growth\n              window, yielding maximum polarization, dielectric constant, and\n              paraelectric-to-ferroelectric transition temperatures. Outside\n              this growth window, properties are severely deteriorated and\n              ultimately suppressed by defects in the films. This study\n              exemplifies the important role of precise compositional control\n              for achieving strain-induced properties. Untangling the effects\n              of strain and stoichiometry on functional properties will\n              accelerate both fundamental discoveries yet to be made in the\n              vast materials design space of strained complex oxide films, as\n              well as utilization of strain-stabilized phenomena in future\n              devices.",\n  journal  = "Adv. Funct. Mater.",\n  volume   =  26,\n  number   =  40,\n  pages    = "7271--7279",\n  month    =  oct,\n  year     =  2016,\n  keywords = "ferroelectric thin films; hybrid molecular beam epitaxy;\n              perovskites; stoichiometry control;Ferroelectric thin\n              films;Perovskites;hybrid molecular beam epitaxy;stoichiometry\n              control;LeBeau Group",\n  issn     = "1616-301X",\n  doi      = "10.1002/adfm.201602767"\n}\n\n
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\n © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Strain tuning has emerged as a powerful means to enhance properties and to induce otherwise unattainable phenomena in complex oxide films. However, by employing strain alone, the predicted properties sometimes fail to emerge. In this work, the critical role of precise stoichiometry control for realizing strain-induced ferroelectricity in CaTiO 3 films is demonstrated. An adsorption controlled growth window is discovered for CaTiO 3 films grown by hybrid molecular beam epitaxy, which ensures an excellent control over the Ti:Ca atomic percent ratio of < 0.8% in the films. Superior ferroelectric and dielectric properties are found for films grown inside the stoichiometric growth window, yielding maximum polarization, dielectric constant, and paraelectric-to-ferroelectric transition temperatures. Outside this growth window, properties are severely deteriorated and ultimately suppressed by defects in the films. This study exemplifies the important role of precise compositional control for achieving strain-induced properties. Untangling the effects of strain and stoichiometry on functional properties will accelerate both fundamental discoveries yet to be made in the vast materials design space of strained complex oxide films, as well as utilization of strain-stabilized phenomena in future devices.\n
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\n \n\n \n \n \n \n \n Structural Changes Underlying Field-Cycling Phenomena in Ferroelectric HfO$_2$ Thin Films.\n \n \n \n\n\n \n Grimley, E. D, Schenk, T., Sang, X., Pe ̌sić, M., Schroeder, U., Mikolajick, T., & LeBeau, J. M\n\n\n \n\n\n\n Advanced Electronic Materials, 2(9): 1600173. September 2016.\n \n\n\n\n
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@ARTICLE{Grimley2016-nf,\n  title    = "Structural Changes Underlying {Field-Cycling} Phenomena in\n              Ferroelectric {HfO$_2$} Thin Films",\n  author   = "Grimley, Everett D and Schenk, Tony and Sang, Xiahan and Pe{\\v\n              s}i{\\'c}, Milan and Schroeder, Uwe and Mikolajick, Thomas and\n              LeBeau, James M",\n  journal  = "Advanced Electronic Materials",\n  volume   =  2,\n  number   =  9,\n  pages    = "1600173",\n  month    =  sep,\n  year     =  2016,\n  keywords = "Ferroelectrics; Hafnium oxide; Impedance spectroscopy; Scanning\n              transmission electron microscopy; Thin films;LeBeau\n              Group;HfO2;DHS proposal",\n  issn     = "2199-160X",\n  doi      = "10.1002/aelm.201600173"\n}\n\n
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\n \n\n \n \n \n \n \n Structure and magnetic properties of a multi-principal element Ni–Fe–Cr–Co–Zn–Mn alloy.\n \n \n \n\n\n \n Zaddach, A J, Niu, C, Oni, A A, Fan, M, LeBeau, J. M, Irving, D L, & Koch, C C\n\n\n \n\n\n\n Intermetallics, 68: 107–112. January 2016.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Zaddach2016-iw,\n  title    = "Structure and magnetic properties of a multi-principal element\n              {Ni--Fe--Cr--Co--Zn--Mn} alloy",\n  author   = "Zaddach, A J and Niu, C and Oni, A A and Fan, M and LeBeau, James\n              M and Irving, D L and Koch, C C",\n  abstract = "\\copyright{} 2015 Elsevier Ltd. All rights reserved. A\n              nanocrystalline alloy with a nominal composition of Ni 20 Fe 20\n              Cr 20 Co 20 Zn 15 Mn 5 was produced by mechanical alloying and\n              processed using annealing treatments between 450 and 600°C for\n              lengths from 0.5 to 4 h. Analysis was conducted using x-ray\n              diffraction, transmission electron microscopy, magnetometry, and\n              first-principles calculations. Despite designing the alloy using\n              empirical high-entropy alloy guidelines, it was found to\n              precipitate numerous phases after annealing. These precipitates\n              included a magnetic phase, $\\alpha$-FeCo, which, after the\n              optimal heat treatment conditions of 1 h at 500°C, resulted in an\n              alloy with reasonably good hard magnetic properties. The effect\n              of annealing temperature and time on the microstructure and\n              magnetic properties are discussed, as well as the likely\n              mechanisms that cause the microstructure development.",\n  journal  = "Intermetallics",\n  volume   =  68,\n  pages    = "107--112",\n  month    =  jan,\n  year     =  2016,\n  keywords = "Ab--initio calculations; Electron microscopy; Magnetic\n              properties; Mechanical alloying and milling; Nanocrystalline\n              metals; Phase stability; transmission;LeBeau Group;HEA\n              DMREF;AFOSR - YIP",\n  issn     = "0966-9795",\n  doi      = "10.1016/j.intermet.2015.09.009"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n © 2015 Elsevier Ltd. All rights reserved. A nanocrystalline alloy with a nominal composition of Ni 20 Fe 20 Cr 20 Co 20 Zn 15 Mn 5 was produced by mechanical alloying and processed using annealing treatments between 450 and 600°C for lengths from 0.5 to 4 h. Analysis was conducted using x-ray diffraction, transmission electron microscopy, magnetometry, and first-principles calculations. Despite designing the alloy using empirical high-entropy alloy guidelines, it was found to precipitate numerous phases after annealing. These precipitates included a magnetic phase, $α$-FeCo, which, after the optimal heat treatment conditions of 1 h at 500°C, resulted in an alloy with reasonably good hard magnetic properties. The effect of annealing temperature and time on the microstructure and magnetic properties are discussed, as well as the likely mechanisms that cause the microstructure development.\n
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\n \n\n \n \n \n \n \n Atom site preference and $γ$′/$γ$ mismatch strain in NiAlCoTi superalloys.\n \n \n \n\n\n \n Oni, A A, Broderick, S R, Rajan, K, & LeBeau, J M\n\n\n \n\n\n\n Intermetallics, 73: 72–78. June 2016.\n \n\n\n\n
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@ARTICLE{Oni2016-er,\n  title    = "Atom site preference and $\\gamma$′/$\\gamma$ mismatch strain in\n              {NiAlCoTi} superalloys",\n  author   = "Oni, A A and Broderick, S R and Rajan, K and LeBeau, J M",\n  abstract = "The structure and chemistry of NiCoAlTi quaternary superalloys\n              are investigated at the microstructural and atomic scale. Atom\n              probe tomograghy (APT) is used to quantify phase compositions and\n              elemental partitioning behavior. Using aberration corrected\n              electron microscopy, the site occupancy of the atoms within the\n              A3 B structure (L12--type) $\\gamma$′ phase is determined via\n              atomic resolution energy dispersive X-ray spectroscopy (EDX). Ni\n              is observed to preferentially occupy the A sub-lattice positions\n              for all alloys, while Al and Ti occupy the B sub-lattice. In\n              contrast, Co's site preference changes from a random distribution\n              to the A sub-lattice as the alloy composition changes, in\n              agreement with theoretical predictions from literature. Finally,\n              the lattice strain across the $\\gamma$′/$\\gamma$ interfaces is\n              measured as a function of alloy composition.",\n  journal  = "Intermetallics",\n  volume   =  73,\n  pages    = "72--78",\n  month    =  jun,\n  year     =  2016,\n  keywords = "quaternary superalloy; scanning transmission electron microscopy;\n              Site preference; Strain measurement;LeBeau Group;AFOSR - YIP",\n  issn     = "0966-9795",\n  doi      = "10.1016/j.intermet.2016.03.006"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n The structure and chemistry of NiCoAlTi quaternary superalloys are investigated at the microstructural and atomic scale. Atom probe tomograghy (APT) is used to quantify phase compositions and elemental partitioning behavior. Using aberration corrected electron microscopy, the site occupancy of the atoms within the A3 B structure (L12–type) $γ$′ phase is determined via atomic resolution energy dispersive X-ray spectroscopy (EDX). Ni is observed to preferentially occupy the A sub-lattice positions for all alloys, while Al and Ti occupy the B sub-lattice. In contrast, Co's site preference changes from a random distribution to the A sub-lattice as the alloy composition changes, in agreement with theoretical predictions from literature. Finally, the lattice strain across the $γ$′/$γ$ interfaces is measured as a function of alloy composition.\n
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\n \n\n \n \n \n \n \n Characterizing the response of a scintillator-based detector to single electrons.\n \n \n \n\n\n \n Sang, X., & LeBeau, J. M\n\n\n \n\n\n\n Ultramicroscopy, 161: 3–9. February 2016.\n \n\n\n\n
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@ARTICLE{Sang2016-oz,\n  title     = "Characterizing the response of a scintillator-based detector to\n               single electrons",\n  author    = "Sang, Xiahan and LeBeau, James M",\n  abstract  = "Here we report the response of a high angle annular dark field\n               scintillator-based detector to single electrons. We demonstrate\n               that care must be taken when determining the single electron\n               intensity as significant discrepancies can occur when\n               quantifying STEM images with different methods. To account for\n               the detector response, we first image the detector using very\n               low beam currents (∼8fA), and subsequently model the interval\n               between consecutive single electrons events. We find that single\n               electrons striking the detector present a wide distribution of\n               intensities, which we show is not described by a simple\n               function. Further, we present a method to accurately account for\n               the electrons within the incident probe when conducting\n               quantitative imaging. The role detector settings play on\n               determining the single electron intensity is also explored.\n               Finally, we extend our analysis to describe the response of the\n               detector to multiple electron events within the dwell interval\n               of each pixel.",\n  journal   = "Ultramicroscopy",\n  publisher = "Elsevier BV",\n  volume    =  161,\n  pages     = "3--9",\n  month     =  feb,\n  year      =  2016,\n  keywords  = "Detector response; Quantitative imaging; STEM; Scintillator;\n               Single electron counting;LeBeau\n               Group;QSTEMChapter;Detector;AFOSR - YIP",\n  language  = "en",\n  issn      = "0304-3991, 1879-2723",\n  pmid      = "26624510",\n  doi       = "10.1016/j.ultramic.2015.11.008"\n}\n\n
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\n Here we report the response of a high angle annular dark field scintillator-based detector to single electrons. We demonstrate that care must be taken when determining the single electron intensity as significant discrepancies can occur when quantifying STEM images with different methods. To account for the detector response, we first image the detector using very low beam currents (∼8fA), and subsequently model the interval between consecutive single electrons events. We find that single electrons striking the detector present a wide distribution of intensities, which we show is not described by a simple function. Further, we present a method to accurately account for the electrons within the incident probe when conducting quantitative imaging. The role detector settings play on determining the single electron intensity is also explored. Finally, we extend our analysis to describe the response of the detector to multiple electron events within the dwell interval of each pixel.\n
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\n \n\n \n \n \n \n \n A numerical model for multiple detector energy dispersive X-ray spectroscopy in the transmission electron microscope.\n \n \n \n\n\n \n Xu, W, Dycus, J H, Sang, X, & LeBeau, J M\n\n\n \n\n\n\n Ultramicroscopy, 164: 51–61. May 2016.\n \n\n\n\n
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@ARTICLE{Xu2016-kv,\n  title    = "A numerical model for multiple detector energy dispersive X-ray\n              spectroscopy in the transmission electron microscope",\n  author   = "Xu, W and Dycus, J H and Sang, X and LeBeau, J M",\n  abstract = "Here we report a numerical approach to model a four quadrant\n              energy dispersive X-ray spectrometer in the transmission electron\n              microscope. The model includes detector geometries, specimen\n              position and absorption, shadowing by the holder, and filtering\n              by the Be carrier. We show that this comprehensive model\n              accurately predicts absolute counts and intensity ratios as a\n              function of specimen tilt and position. We directly compare the\n              model to experimental results acquired with a FEI Super-X EDS\n              four quadrant detector. The contribution from each detector to\n              the sum is investigated. The program and source code can be\n              downloaded from https://github.com/subangstrom/superAngle.",\n  journal  = "Ultramicroscopy",\n  volume   =  164,\n  pages    = "51--61",\n  month    =  may,\n  year     =  2016,\n  keywords = "Detector collection angle; Energy dispersive X-ray spectroscopy\n              (EDS); Shadowing; Spurious X-rays; Super-X; X-ray absorption\n              correction;LeBeau Group;AFOSR - YIP",\n  issn     = "0304-3991",\n  pmid     = "26948674",\n  doi      = "10.1016/j.ultramic.2016.02.004"\n}\n\n
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\n Here we report a numerical approach to model a four quadrant energy dispersive X-ray spectrometer in the transmission electron microscope. The model includes detector geometries, specimen position and absorption, shadowing by the holder, and filtering by the Be carrier. We show that this comprehensive model accurately predicts absolute counts and intensity ratios as a function of specimen tilt and position. We directly compare the model to experimental results acquired with a FEI Super-X EDS four quadrant detector. The contribution from each detector to the sum is investigated. The program and source code can be downloaded from https://github.com/subangstrom/superAngle.\n
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\n \n\n \n \n \n \n \n Quantitative atomic resolution elemental mapping via absolute-scale energy dispersive X-ray spectroscopy.\n \n \n \n\n\n \n Chen, Z, Weyland, M, Sang, X, Xu, W, Dycus, J H, LeBeau, J. M, D'Alfonso, A J, Allen, L J, & Findlay, S D\n\n\n \n\n\n\n Ultramicroscopy, 168: 7–16. September 2016.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n  \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Chen2016-ra,\n  title    = "Quantitative atomic resolution elemental mapping via\n              absolute-scale energy dispersive X-ray spectroscopy",\n  author   = "Chen, Z and Weyland, M and Sang, X and Xu, W and Dycus, J H and\n              LeBeau, James M and D'Alfonso, A J and Allen, L J and Findlay, S\n              D",\n  abstract = "\\copyright{} 2016 Elsevier B.V. Quantitative agreement on an\n              absolute scale is demonstrated between experiment and simulation\n              for two-dimensional, atomic-resolution elemental mapping via\n              energy dispersive X-ray spectroscopy. This requires all\n              experimental parameters to be carefully characterized. The\n              agreement is good, but some discrepancies remain. The most likely\n              contributing factors are identified and discussed. Previous\n              predictions that increasing the probe forming aperture helps to\n              suppress the channelling enhancement in the average signal are\n              confirmed experimentally. It is emphasized that simple\n              column-by-column analysis requires a choice of sample thickness\n              that compromises between being thick enough to yield a good\n              signal-to-noise ratio while being thin enough that the\n              overwhelming majority of the EDX signal derives from the column\n              on which the probe is placed, despite strong electron scattering\n              effects.",\n  journal  = "Ultramicroscopy",\n  volume   =  168,\n  pages    = "7--16",\n  month    =  sep,\n  year     =  2016,\n  keywords = "Atomic-resolution mapping; Elemental quantification; Energy\n              dispersive X-ray (EDX) spectroscopy; Scanning transmission\n              electron microscopy (STEM); scanning transmission electron\n              microscopy;LeBeau Group;AFOSR - YIP",\n  issn     = "0304-3991",\n  doi      = "10.1016/j.ultramic.2016.05.008"\n}\n\n
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\n © 2016 Elsevier B.V. Quantitative agreement on an absolute scale is demonstrated between experiment and simulation for two-dimensional, atomic-resolution elemental mapping via energy dispersive X-ray spectroscopy. This requires all experimental parameters to be carefully characterized. The agreement is good, but some discrepancies remain. The most likely contributing factors are identified and discussed. Previous predictions that increasing the probe forming aperture helps to suppress the channelling enhancement in the average signal are confirmed experimentally. It is emphasized that simple column-by-column analysis requires a choice of sample thickness that compromises between being thick enough to yield a good signal-to-noise ratio while being thin enough that the overwhelming majority of the EDX signal derives from the column on which the probe is placed, despite strong electron scattering effects.\n
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\n \n\n \n \n \n \n \n Influence of experimental conditions on atom column visibility in energy dispersive X-ray spectroscopy.\n \n \n \n\n\n \n Dycus, J H, Xu, W, Sang, X, D'Alfonso, A J, Chen, Z, Weyland, M, Allen, L J, Findlay, S D, & LeBeau, J M M\n\n\n \n\n\n\n Ultramicroscopy, 171: 1–7. August 2016.\n \n\n\n\n
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@ARTICLE{Dycus2016-ep,\n  title    = "Influence of experimental conditions on atom column visibility in\n              energy dispersive X-ray spectroscopy",\n  author   = "Dycus, J H and Xu, W and Sang, X and D'Alfonso, A J and Chen, Z\n              and Weyland, M and Allen, L J and Findlay, S D and LeBeau, J M M",\n  abstract = "\\copyright{} 2016 Elsevier B.V. Here we report the influence of\n              key experimental parameters on atomically resolved energy\n              dispersive X-ray spectroscopy (EDX). In particular, we examine\n              the role of the probe forming convergence semi-angle, sample\n              thickness, lattice spacing, and dwell/collection time. We show\n              that an optimum specimen-dependent probe forming convergence\n              angle exists to maximize the signal-to-noise ratio of the\n              atomically resolved signal in EDX mapping. Furthermore, we\n              highlight that it can be important to select an appropriate dwell\n              time to efficiently process the X-ray signal. These practical\n              considerations provide insight for experimental parameters in\n              atomic resolution energy dispersive X-ray analysis.",\n  journal  = "Ultramicroscopy",\n  volume   =  171,\n  pages    = "1--7",\n  month    =  aug,\n  year     =  2016,\n  keywords = "Atomic resolution; Electron channeling; Energy-dispersive X-ray\n              spectroscopy; Probe convergence angle; Scanning transmission\n              electron microscopy (STEM); scanning transmission electron\n              microscopy;LeBeau Group",\n  issn     = "0304-3991",\n  doi      = "10.1016/j.ultramic.2016.08.013"\n}\n\n
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\n © 2016 Elsevier B.V. Here we report the influence of key experimental parameters on atomically resolved energy dispersive X-ray spectroscopy (EDX). In particular, we examine the role of the probe forming convergence semi-angle, sample thickness, lattice spacing, and dwell/collection time. We show that an optimum specimen-dependent probe forming convergence angle exists to maximize the signal-to-noise ratio of the atomically resolved signal in EDX mapping. Furthermore, we highlight that it can be important to select an appropriate dwell time to efficiently process the X-ray signal. These practical considerations provide insight for experimental parameters in atomic resolution energy dispersive X-ray analysis.\n
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\n \n\n \n \n \n \n \n Competing pathways for nucleation of the double perovskite structure in the epitaxial synthesis of La$_2$MnNiO$_6$.\n \n \n \n\n\n \n Spurgeon, S. R S R, Du, Y., Droubay, T., Devaraj, A., Sang, X., Longo, P., Yan, P., Kotula, P G P. G, Shutthanandan, V., Bowden, M. E M E, LeBeau, J. M, Wang, C., Sushko, P. V P V, & Chambers, S A S. A\n\n\n \n\n\n\n Chem. Mater., 28(11): 3814–3822. June 2016.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Spurgeon2016-vu,\n  title    = "Competing pathways for nucleation of the double perovskite\n              structure in the epitaxial synthesis of {La$_2$MnNiO$_6$}",\n  author   = "Spurgeon, Steven R S R and Du, Yingge and Droubay, Timothy and\n              Devaraj, Arun and Sang, Xiahan and Longo, Paolo and Yan, Pengfei\n              and Kotula, P G Paul G and Shutthanandan, Vaithiyalingam and\n              Bowden, Mark E M E and LeBeau, James M and Wang, Chongmin and\n              Sushko, Peter V P V and Chambers, S A Scott A",\n  abstract = "\\copyright{} 2016 American Chemical Society. Double perovskites\n              of the form R 2 BB′O 6 (where R is a rare earth cation and B and\n              B′ are chemically distinct transition metal cations with\n              half-filled and empty e g orbitals, respectively) are of\n              significant interest for their magnetoelectric properties. La 2\n              MnNiO 6 is particularly attractive because of its large expected\n              ferromagnetic moment per formula unit (5 $\\mu$ B f.u. -1 ) and\n              its semiconducting character. If the ideal structure nucleates,\n              superexchange coupling can take place via the B - O - B′ bonds\n              that form, and the moment per formula unit can attain its maximum\n              theoretical value. However, we show that even in the case of\n              layer-by-layer deposition via molecular beam epitaxy, the system\n              can follow multiple reaction pathways that lead to deviations\n              from the double perovskite structure. In particular, we observe a\n              spatially extended phase in which B-site cation disorder occurs,\n              resulting in Mn - O - Mn and Ni - O - Ni antiferromagnetic\n              domains, as well as the formation of quasi-epitaxial,\n              antiferromagnetic NiO nanoscale inclusions, surrounded by a\n              Mn-rich double perovskite. The coexistence of the double\n              perovskite and secondary phases in oxygen deficient conditions is\n              supported by first-principles modeling. However, extended\n              annealing in air restores long-range B-site order and begins to\n              dissolve the NiO inclusions, yielding an ideal structure and an\n              enhanced ferromagnetic moment. This study reveals fundamental\n              structure-property relationships that may not be apparent during\n              the design phase of a multielement crystalline solid and\n              illustrates how to engineer a synthetic path to a desired\n              product.",\n  journal  = "Chem. Mater.",\n  volume   =  28,\n  number   =  11,\n  pages    = "3814--3822",\n  month    =  jun,\n  year     =  2016,\n  keywords = "LeBeau Group",\n  issn     = "0897-4756",\n  doi      = "10.1021/acs.chemmater.6b00829"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n © 2016 American Chemical Society. Double perovskites of the form R 2 BB′O 6 (where R is a rare earth cation and B and B′ are chemically distinct transition metal cations with half-filled and empty e g orbitals, respectively) are of significant interest for their magnetoelectric properties. La 2 MnNiO 6 is particularly attractive because of its large expected ferromagnetic moment per formula unit (5 $μ$ B f.u. -1 ) and its semiconducting character. If the ideal structure nucleates, superexchange coupling can take place via the B - O - B′ bonds that form, and the moment per formula unit can attain its maximum theoretical value. However, we show that even in the case of layer-by-layer deposition via molecular beam epitaxy, the system can follow multiple reaction pathways that lead to deviations from the double perovskite structure. In particular, we observe a spatially extended phase in which B-site cation disorder occurs, resulting in Mn - O - Mn and Ni - O - Ni antiferromagnetic domains, as well as the formation of quasi-epitaxial, antiferromagnetic NiO nanoscale inclusions, surrounded by a Mn-rich double perovskite. The coexistence of the double perovskite and secondary phases in oxygen deficient conditions is supported by first-principles modeling. However, extended annealing in air restores long-range B-site order and begins to dissolve the NiO inclusions, yielding an ideal structure and an enhanced ferromagnetic moment. This study reveals fundamental structure-property relationships that may not be apparent during the design phase of a multielement crystalline solid and illustrates how to engineer a synthetic path to a desired product.\n
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\n \n\n \n \n \n \n \n Structure and chemistry of passivated SiC/SiO$_2$ interfaces.\n \n \n \n\n\n \n Houston Dycus, J, Xu, W., Lichtenwalner, D. J, Hull, B., Palmour, J. W, & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 108(20): 201607. May 2016.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Houston_Dycus2016-pt,\n  title    = "Structure and chemistry of passivated {SiC/SiO$_2$} interfaces",\n  author   = "Houston Dycus, J and Xu, Weizong and Lichtenwalner, Daniel J and\n              Hull, Brett and Palmour, John W and LeBeau, James M",\n  journal  = "Appl. Phys. Lett.",\n  volume   =  108,\n  number   =  20,\n  pages    = "201607",\n  month    =  may,\n  year     =  2016,\n  keywords = "LeBeau Group",\n  issn     = "0003-6951",\n  doi      = "10.1063/1.4951677"\n}\n\n
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\n \n\n \n \n \n \n \n Comparison of thermoelectric properties of nanostructured Mg$_2$Si, FeSi$_2$, SiGe, and nanocomposites of SiGe–Mg$_2$Si, SiGe–FeSi$_2$.\n \n \n \n\n\n \n Nozariasbmarz, A., Roy, P., Zamanipour, Z., Dycus, J H., Cabral, M. J, LeBeau, J. M, Krasinski, J. S, & Vashaee, D.\n\n\n \n\n\n\n APL Materials, 4(10): 104814. 2016.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Nozariasbmarz2016-bl,\n  title    = "Comparison of thermoelectric properties of nanostructured\n              {Mg$_2$Si}, {FeSi$_2$}, {SiGe}, and nanocomposites of\n              {SiGe--Mg$_2$Si}, {SiGe--FeSi$_2$}",\n  author   = "Nozariasbmarz, Amin and Roy, Palash and Zamanipour, Zahra and\n              Dycus, J Houston and Cabral, Matthew J and LeBeau, James M and\n              Krasinski, Jerzy S and Vashaee, Daryoosh",\n  journal  = "APL Materials",\n  volume   =  4,\n  number   =  10,\n  pages    = "104814",\n  year     =  2016,\n  keywords = "LeBeau Group",\n  issn     = "2166-532X",\n  doi      = "10.1063/1.4966138"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n \n\n \n \n \n \n \n Processing low-Oxide ZrB$_2$ ceramics with high strength using boron carbide and spark plasma sintering.\n \n \n \n\n\n \n Pham, D., Dycus, J. H., LeBeau, J. M, Manga, V. R, Muralidharan, K., & Corral, E. L\n\n\n \n\n\n\n J. Am. Ceram. Soc., 99(37653): 2585–2592. 2016.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Pham2016-dz,\n  title     = "Processing low-Oxide {ZrB$_2$} ceramics with high strength using\n               boron carbide and spark plasma sintering",\n  author    = "Pham, David and Dycus, Joseph Houston and LeBeau, James M and\n               Manga, Venkateswara R and Muralidharan, Krishna and Corral,\n               Erica L",\n  abstract  = "A phase diagram-assisted powder processing approach is shown to\n               produce low-oxygen (0.06 wt\\%O) ZrB2 ceramics using minimal B4C\n               additions (0.25 wt\\%) and spark plasma sintering. Scanning\n               electron microscopy and scanning transmission electron\n               microscopy with elemental spectroscopy are used to identify\n               ``trash collector'' oxides. These ``trash collector'' oxides are\n               composed of manufacturer metal powder impurities that form\n               discreet oxide particles due to the absence of standard Zr--B\n               oxides found in high oxygen samples. A preliminary Zr--B--C--O\n               quaternary thermodynamic database developed as a part of this\n               work was used to calculate the ZrO2--B4C pseudobinary phase\n               diagram and ZrB2--ZrO2--B4C pseudoternary phase diagrams. We use\n               the calculated equilibrium phase diagrams to characterize the\n               oxide impurities and show the direct reaction path that allows\n               for the formation of ZrB2 with an oxygen content of 0.06 wt\\%,\n               fine grains (3.3 $\\mu$m) and superior mechanical properties\n               (flexural strength of 660 MPa).",\n  journal   = "J. Am. Ceram. Soc.",\n  publisher = "Wiley Online Library",\n  volume    =  99,\n  number    =  37653,\n  pages     = "2585--2592",\n  year      =  2016,\n  keywords  = "microscopy; processing; spark plasma sintering; transmission\n               electron; ultra-high temperature ceramics; zirconium/zirconium\n               compounds;LeBeau Group",\n  issn      = "0002-7820",\n  doi       = "10.1111/jace.14253"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n A phase diagram-assisted powder processing approach is shown to produce low-oxygen (0.06 wt%O) ZrB2 ceramics using minimal B4C additions (0.25 wt%) and spark plasma sintering. Scanning electron microscopy and scanning transmission electron microscopy with elemental spectroscopy are used to identify ``trash collector'' oxides. These ``trash collector'' oxides are composed of manufacturer metal powder impurities that form discreet oxide particles due to the absence of standard Zr–B oxides found in high oxygen samples. A preliminary Zr–B–C–O quaternary thermodynamic database developed as a part of this work was used to calculate the ZrO2–B4C pseudobinary phase diagram and ZrB2–ZrO2–B4C pseudoternary phase diagrams. We use the calculated equilibrium phase diagrams to characterize the oxide impurities and show the direct reaction path that allows for the formation of ZrB2 with an oxygen content of 0.06 wt%, fine grains (3.3 $μ$m) and superior mechanical properties (flexural strength of 660 MPa).\n
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\n \n\n \n \n \n \n \n Combined experimental and computational methods reveal the evolution of buried interfaces during synthesis of ferroelectric thin films.\n \n \n \n\n\n \n Jones, J. L, LeBeau, J. M, Nikkel, J., Oni, A. A, Dycus, J H., Cozzan, C., Lin, F., Chernatynskiy, A., Nino, J. C, Sinnott, S. B, Mhin, S., Brennecka, G. L, & Ihlefeld, J.\n\n\n \n\n\n\n Advanced Materials Interfaces, 2(10): 1500181. July 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Jones2015-eo,\n  title    = "Combined experimental and computational methods reveal the\n              evolution of buried interfaces during synthesis of ferroelectric\n              thin films",\n  author   = "Jones, Jacob L and LeBeau, James M and Nikkel, Jason and Oni,\n              Adedapo A and Dycus, J Houston and Cozzan, Clayton and Lin,\n              Fang-Yin and Chernatynskiy, Aleksandr and Nino, Juan C and\n              Sinnott, Susan B and Mhin, Sungwook and Brennecka, Geoff L and\n              Ihlefeld, Jon",\n  journal  = "Advanced Materials Interfaces",\n  volume   =  2,\n  number   =  10,\n  pages    = "1500181",\n  month    =  jul,\n  year     =  2015,\n  keywords = "LeBeau Group",\n  issn     = "2196-7350",\n  doi      = "10.1002/admi.201500181"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n \n\n \n \n \n \n \n Effect of B and Cr on elastic strength and crystal structure of Ni$_3$Al alloys under high pressure.\n \n \n \n\n\n \n Raju, S V, Oni, A A, Godwal, B K, Yan, J, Drozd, V, Srinivasan, S, LeBeau, J M, Rajan, K, & Saxena, S K\n\n\n \n\n\n\n J. Alloys Compd., 619: 616–620. January 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Raju2015-dd,\n  title    = "Effect of {B} and Cr on elastic strength and crystal structure of\n              {Ni$_3$Al} alloys under high pressure",\n  author   = "Raju, S V and Oni, A A and Godwal, B K and Yan, J and Drozd, V\n              and Srinivasan, S and LeBeau, J M and Rajan, K and Saxena, S K",\n  abstract = "Samples of Ni3Al, Ni3Al:B and Ni--Al--Cr super alloys were\n              prepared by directional solidification method and their effect of\n              alloying with ternary elements on the mechanical properties was\n              investigated. In-situ X-ray diffraction studies were carried out\n              on undoped Ni3Al, Ni3Al:B with boron 500ppm and Ni--Al--Cr with\n              7.5at.\\% of chromium super alloys at high pressure using diamond\n              anvil cell. The results indicate that micro-alloying with B forms\n              $\\gamma$′-phase (L12 structure), similar to the pure Ni 3Al,\n              while Ni--Al--Cr alloy consists of $\\gamma$′ precipitates in a\n              matrix of $\\gamma$-phase (Ni-FCC structure). The crystal\n              structure of all three alloys was stable up to 20GPa. Micro\n              alloying with boron increases bulk modulus of Ni3Al by 8\\%\n              whereas alloying with chromium has the opposite effect decreasing\n              the modulus by 11\\% when compared to undoped alloy. Further, the\n              elastic modulus and hardness of Ni3Al, Ni3Al:B and Ni--Al--Cr\n              alloys were determined using the nano-indentation technique, in\n              combination with compressibility data which enabled the\n              estimation of shear modulus and Poisson's ratio of these alloys.",\n  journal  = "J. Alloys Compd.",\n  volume   =  619,\n  pages    = "616--620",\n  month    =  jan,\n  year     =  2015,\n  keywords = "Elastic properties; High pressure; Nano-indentation; Superalloys;\n              X-ray diffraction;LeBeau Group",\n  issn     = "0925-8388",\n  doi      = "10.1016/j.jallcom.2014.09.012"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Samples of Ni3Al, Ni3Al:B and Ni–Al–Cr super alloys were prepared by directional solidification method and their effect of alloying with ternary elements on the mechanical properties was investigated. In-situ X-ray diffraction studies were carried out on undoped Ni3Al, Ni3Al:B with boron 500ppm and Ni–Al–Cr with 7.5at.% of chromium super alloys at high pressure using diamond anvil cell. The results indicate that micro-alloying with B forms $γ$′-phase (L12 structure), similar to the pure Ni 3Al, while Ni–Al–Cr alloy consists of $γ$′ precipitates in a matrix of $γ$-phase (Ni-FCC structure). The crystal structure of all three alloys was stable up to 20GPa. Micro alloying with boron increases bulk modulus of Ni3Al by 8% whereas alloying with chromium has the opposite effect decreasing the modulus by 11% when compared to undoped alloy. Further, the elastic modulus and hardness of Ni3Al, Ni3Al:B and Ni–Al–Cr alloys were determined using the nano-indentation technique, in combination with compressibility data which enabled the estimation of shear modulus and Poisson's ratio of these alloys.\n
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\n \n\n \n \n \n \n \n Accurate nanoscale crystallography in real-space using scanning transmission electron microscopy.\n \n \n \n\n\n \n Dycus, J H., Harris, J. S, Sang, X., Fancher, C. M, Findlay, S. D, Oni, A. A, Chan, T. E, Koch, C. C, Jones, J. L, Allen, L. J, Irving, D. L, & LeBeau, J. M\n\n\n \n\n\n\n Microsc. Microanal., 21(04): 946–952. August 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Dycus2015-qu,\n  title    = "Accurate nanoscale crystallography in real-space using scanning\n              transmission electron microscopy",\n  author   = "Dycus, J Houston and Harris, Joshua S and Sang, Xiahan and\n              Fancher, Chris M and Findlay, Scott D and Oni, Adedapo A and\n              Chan, Tsung-Ta E and Koch, Carl C and Jones, Jacob L and Allen,\n              Leslie J and Irving, Douglas L and LeBeau, James M",\n  abstract = "Here, we report reproducible and accurate measurement of\n              crystallographic parameters using scanning transmission electron\n              microscopy. This is made possible by removing drift and residual\n              scan distortion. We demonstrate real-space lattice parameter\n              measurements with <0.1\\% error for complex-layered chalcogenides\n              Bi 2 Te 3 , Bi 2 Se 3 , and a Bi 2 Te 2.7 Se 0.3 nanostructured\n              alloy. Pairing the technique with atomic resolution spectroscopy,\n              we connect local structure with chemistry and bonding. Combining\n              these results with density functional theory, we show that the\n              incorporation of Se into Bi 2 Te 3 causes charge redistribution\n              that anomalously increases the van der Waals gap between building\n              blocks of the layered structure. The results show that atomic\n              resolution imaging with electrons can accurately and robustly\n              quantify crystallography at the nanoscale.",\n  journal  = "Microsc. Microanal.",\n  volume   =  21,\n  number   =  04,\n  pages    = "946--952",\n  month    =  aug,\n  year     =  2015,\n  keywords = "LeBeau Group",\n  issn     = "1431-9276",\n  doi      = "10.1017/S1431927615013732"\n}\n\n
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\n Here, we report reproducible and accurate measurement of crystallographic parameters using scanning transmission electron microscopy. This is made possible by removing drift and residual scan distortion. We demonstrate real-space lattice parameter measurements with <0.1% error for complex-layered chalcogenides Bi 2 Te 3 , Bi 2 Se 3 , and a Bi 2 Te 2.7 Se 0.3 nanostructured alloy. Pairing the technique with atomic resolution spectroscopy, we connect local structure with chemistry and bonding. Combining these results with density functional theory, we show that the incorporation of Se into Bi 2 Te 3 causes charge redistribution that anomalously increases the van der Waals gap between building blocks of the layered structure. The results show that atomic resolution imaging with electrons can accurately and robustly quantify crystallography at the nanoscale.\n
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\n \n\n \n \n \n \n \n Mapping Chemical Selection Pathways for Designing Multicomponent Alloys: an informatics framework for materials design.\n \n \n \n\n\n \n Srinivasan, S., Broderick, S. R, Zhang, R., Mishra, A., Sinnott, S. B, Saxena, S. K, LeBeau, J. M, & Rajan, K.\n\n\n \n\n\n\n Sci. Rep., 5(October): 17960. December 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Srinivasan2015-rs,\n  title     = "Mapping Chemical Selection Pathways for Designing Multicomponent\n               Alloys: an informatics framework for materials design",\n  author    = "Srinivasan, Srikant and Broderick, Scott R and Zhang, Ruifeng\n               and Mishra, Amrita and Sinnott, Susan B and Saxena, Surendra K\n               and LeBeau, James M and Rajan, Krishna",\n  abstract  = "A data driven methodology is developed for tracking the\n               collective influence of the multiple attributes of alloying\n               elements on both thermodynamic and mechanical properties of\n               metal alloys. Cobalt-based superalloys are used as a template to\n               demonstrate the approach. By mapping the high dimensional nature\n               of the systematics of elemental data embedded in the periodic\n               table into the form of a network graph, one can guide targeted\n               first principles calculations that identify the influence of\n               specific elements on phase stability, crystal structure and\n               elastic properties. This provides a fundamentally new means to\n               rapidly identify new stable alloy chemistries with enhanced high\n               temperature properties. The resulting visualization scheme\n               exhibits the grouping and proximity of elements based on their\n               impact on the properties of intermetallic alloys. Unlike the\n               periodic table however, the distance between neighboring\n               elements uncovers relationships in a complex high dimensional\n               information space that would not have been easily seen\n               otherwise. The predictions of the methodology are found to be\n               consistent with reported experimental and theoretical studies.\n               The informatics based methodology presented in this study can be\n               generalized to a framework for data analysis and knowledge\n               discovery that can be applied to many material systems and\n               recreated for different design objectives.",\n  journal   = "Sci. Rep.",\n  publisher = "Nature Publishing Group",\n  volume    =  5,\n  number    = "October",\n  pages     = "17960",\n  month     =  dec,\n  year      =  2015,\n  keywords  = "LeBeau Group;AFOSR - YIP",\n  language  = "en",\n  issn      = "2045-2322",\n  pmid      = "26681142",\n  doi       = "10.1038/srep17960",\n  pmc       = "PMC4683530"\n}\n\n
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\n A data driven methodology is developed for tracking the collective influence of the multiple attributes of alloying elements on both thermodynamic and mechanical properties of metal alloys. Cobalt-based superalloys are used as a template to demonstrate the approach. By mapping the high dimensional nature of the systematics of elemental data embedded in the periodic table into the form of a network graph, one can guide targeted first principles calculations that identify the influence of specific elements on phase stability, crystal structure and elastic properties. This provides a fundamentally new means to rapidly identify new stable alloy chemistries with enhanced high temperature properties. The resulting visualization scheme exhibits the grouping and proximity of elements based on their impact on the properties of intermetallic alloys. Unlike the periodic table however, the distance between neighboring elements uncovers relationships in a complex high dimensional information space that would not have been easily seen otherwise. The predictions of the methodology are found to be consistent with reported experimental and theoretical studies. The informatics based methodology presented in this study can be generalized to a framework for data analysis and knowledge discovery that can be applied to many material systems and recreated for different design objectives.\n
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\n \n\n \n \n \n \n \n Large area strain analysis using scanning transmission electron microscopy across multiple images.\n \n \n \n\n\n \n Oni, A A, Sang, X, Raju, S V, Dumpala, S, Broderick, S, Kumar, A, Sinnott, S, Saxena, S, Rajan, K, & LeBeau, J M\n\n\n \n\n\n\n Appl. Phys. Lett., 106(1): 011601. January 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n  \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Oni2015-yz,\n  title     = "Large area strain analysis using scanning transmission electron\n               microscopy across multiple images",\n  author    = "Oni, A A and Sang, X and Raju, S V and Dumpala, S and Broderick,\n               S and Kumar, A and Sinnott, S and Saxena, S and Rajan, K and\n               LeBeau, J M",\n  abstract  = "Here, we apply revolving scanning transmission electron\n               microscopy to measure lattice strain across a sample using a\n               single reference area. To do so, we remove image distortion\n               introduced by sample drift, which usually restricts strain\n               analysis to a single image. Overcoming this challenge, we show\n               that it is possible to use strain reference areas elsewhere in\n               the sample, thereby enabling reliable strain mapping across\n               large areas. As a prototypical example, we determine the strain\n               present within the microstructure of a Ni-based superalloy\n               directly from atom column positions as well as geometric phase\n               analysis. While maintaining atomic resolution, we quantify\n               strain within nanoscale regions and demonstrate that large,\n               unit-cell level strain fluctuations are present within the\n               intermetallic phase.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "AIP Publishing",\n  volume    =  106,\n  number    =  1,\n  pages     = "011601",\n  month     =  jan,\n  year      =  2015,\n  keywords  = "LeBeau Group",\n  issn      = "0003-6951",\n  doi       = "10.1063/1.4905368"\n}\n\n
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\n Here, we apply revolving scanning transmission electron microscopy to measure lattice strain across a sample using a single reference area. To do so, we remove image distortion introduced by sample drift, which usually restricts strain analysis to a single image. Overcoming this challenge, we show that it is possible to use strain reference areas elsewhere in the sample, thereby enabling reliable strain mapping across large areas. As a prototypical example, we determine the strain present within the microstructure of a Ni-based superalloy directly from atom column positions as well as geometric phase analysis. While maintaining atomic resolution, we quantify strain within nanoscale regions and demonstrate that large, unit-cell level strain fluctuations are present within the intermetallic phase.\n
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\n \n\n \n \n \n \n \n Direct observation of charge mediated lattice distortions in complex oxide solid solutions.\n \n \n \n\n\n \n Sang, X., Grimley, E. D, Niu, C., Irving, D. L, & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 106(6): 061913. February 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n  \n \n 1 download\n \n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Sang2015-xa,\n  title     = "Direct observation of charge mediated lattice distortions in\n               complex oxide solid solutions",\n  author    = "Sang, Xiahan and Grimley, Everett D and Niu, Changning and\n               Irving, Douglas L and LeBeau, James M",\n  abstract  = "Using aberration corrected scanning transmission electron\n               microscopy combined with advanced imaging methods, we directly\n               observe atom column specific, picometer-scale displacements\n               induced by local chemistry in a complex oxide solid solution.\n               Displacements predicted from density functional theory were\n               found to correlate with the observed experimental trends.\n               Further analysis of bonding and charge distribution was used to\n               clarify the mechanisms responsible for the detected structural\n               behavior. By extending the experimental electron microscopy\n               measurements to previously inaccessible length scales, we\n               identified correlated atomic displacements linked to bond\n               differences within the complex oxide structure.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "American Institute of Physics",\n  volume    =  106,\n  number    =  6,\n  pages     = "061913",\n  month     =  feb,\n  year      =  2015,\n  keywords  = "LeBeau Group;HfO2;QSTEMChapter",\n  issn      = "0003-6951",\n  doi       = "10.1063/1.4908124"\n}\n\n
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\n Using aberration corrected scanning transmission electron microscopy combined with advanced imaging methods, we directly observe atom column specific, picometer-scale displacements induced by local chemistry in a complex oxide solid solution. Displacements predicted from density functional theory were found to correlate with the observed experimental trends. Further analysis of bonding and charge distribution was used to clarify the mechanisms responsible for the detected structural behavior. By extending the experimental electron microscopy measurements to previously inaccessible length scales, we identified correlated atomic displacements linked to bond differences within the complex oxide structure.\n
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\n \n\n \n \n \n \n \n Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo.\n \n \n \n\n\n \n Niu, C, Zaddach, A J, Oni, A A, Sang, X, Hurt, J W, LeBeau, J M, Koch, C C, & Irving, D L\n\n\n \n\n\n\n Appl. Phys. Lett., 106(16): 161906. April 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Niu2015-rh,\n  title     = "Spin-driven ordering of Cr in the equiatomic high entropy alloy\n               {NiFeCrCo}",\n  author    = "Niu, C and Zaddach, A J and Oni, A A and Sang, X and Hurt, J W\n               and LeBeau, J M and Koch, C C and Irving, D L",\n  abstract  = "Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high\n               entropy alloy (HEA) was predicted by first-principles\n               calculations. Ordering of Cr is driven by the reduction in\n               energy realized by surrounding anti-ferromagnetic Cr with\n               ferromagnetic Ni, Fe, and Co in an alloyed L12 structure. The\n               fully Cr-ordered alloyed L12 phase was predicted to have a\n               magnetic moment that is 36\\% of that for the magnetically\n               frustrated random solid solution. Three samples were synthesized\n               by milling or casting/annealing. The cast/annealed sample was\n               found to have a low temperature magnetic moment that is 44\\% of\n               the moment in the milled sample, which is consistent with\n               theoretical predictions for ordering. Scanning transmission\n               electron microscopy measurements were performed and the presence\n               of ordered nano-domains in cast/annealed samples throughout the\n               equiatomic NiFeCrCo HEA was identified.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "AIP Publishing",\n  volume    =  106,\n  number    =  16,\n  pages     = "161906",\n  month     =  apr,\n  year      =  2015,\n  keywords  = "LeBeau Group;HEA DMREF;HfO2",\n  issn      = "0003-6951",\n  doi       = "10.1063/1.4918996"\n}\n\n
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\n Spin-driven ordering of Cr in an equiatomic fcc NiFeCrCo high entropy alloy (HEA) was predicted by first-principles calculations. Ordering of Cr is driven by the reduction in energy realized by surrounding anti-ferromagnetic Cr with ferromagnetic Ni, Fe, and Co in an alloyed L12 structure. The fully Cr-ordered alloyed L12 phase was predicted to have a magnetic moment that is 36% of that for the magnetically frustrated random solid solution. Three samples were synthesized by milling or casting/annealing. The cast/annealed sample was found to have a low temperature magnetic moment that is 44% of the moment in the milled sample, which is consistent with theoretical predictions for ordering. Scanning transmission electron microscopy measurements were performed and the presence of ordered nano-domains in cast/annealed samples throughout the equiatomic NiFeCrCo HEA was identified.\n
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\n \n\n \n \n \n \n \n On the structural origins of ferroelectricity in HfO2 thin films.\n \n \n \n\n\n \n Sang, X., Grimley, E. D, Schenk, T., Schroeder, U., & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 106(16): 162905. April 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Sang2015-qh,\n  title     = "On the structural origins of ferroelectricity in {HfO2} thin\n               films",\n  author    = "Sang, Xiahan and Grimley, Everett D and Schenk, Tony and\n               Schroeder, Uwe and LeBeau, James M",\n  abstract  = "Here, we present a structural study on the origin of\n               ferroelectricity in Gd doped HfO2 thin films. We apply\n               aberration corrected high-angle annular dark-field scanning\n               transmission electron microscopy to directly determine the\n               underlying lattice type using projected atom positions and\n               measured lattice parameters. Furthermore, we apply nanoscale\n               electron diffraction methods to visualize the crystal symmetry\n               elements. Combined, the experimental results provide unambiguous\n               evidence for the existence of a non-centrosymmetric orthorhombic\n               phase that can support spontaneous polarization, resolving the\n               origin of ferroelectricity in HfO2 thin films.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "AIP Publishing",\n  volume    =  106,\n  number    =  16,\n  pages     = "162905",\n  month     =  apr,\n  year      =  2015,\n  keywords  = "LeBeau Group;HfO2",\n  issn      = "0003-6951, 1077-3118",\n  doi       = "10.1063/1.4919135"\n}\n\n
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\n Here, we present a structural study on the origin of ferroelectricity in Gd doped HfO2 thin films. We apply aberration corrected high-angle annular dark-field scanning transmission electron microscopy to directly determine the underlying lattice type using projected atom positions and measured lattice parameters. Furthermore, we apply nanoscale electron diffraction methods to visualize the crystal symmetry elements. Combined, the experimental results provide unambiguous evidence for the existence of a non-centrosymmetric orthorhombic phase that can support spontaneous polarization, resolving the origin of ferroelectricity in HfO2 thin films.\n
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\n \n\n \n \n \n \n \n Thickness dependence of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$ magnetoelectric interfaces.\n \n \n \n\n\n \n Zhou, J., Tra, V. T., Dong, S., Trappen, R., Marcus, M. A, Jenkins, C., Frye, C., Wolfe, E., White, R., Polisetty, S., Lin, J., LeBeau, J. M, Chu, Y., & Holcomb, M. B.\n\n\n \n\n\n\n Appl. Phys. Lett., 107(14): 141603. October 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Zhou2015-um,\n  title     = "Thickness dependence of\n               {La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$}\n               magnetoelectric interfaces",\n  author    = "Zhou, Jinling and Tra, Vu Thanh and Dong, Shuai and Trappen,\n               Robbyn and Marcus, Matthew A and Jenkins, Catherine and Frye,\n               Charles and Wolfe, Evan and White, Ryan and Polisetty, Srinivas\n               and Lin, Jiunn-Yuan and LeBeau, James M and Chu, Ying-Hao and\n               Holcomb, Mikel Barry",\n  abstract  = "Magnetoelectric materials have great potential to revolutionize\n               electronic devices due to the coupling of their electric and\n               magnetic properties. Thickness varying La0.7Sr0.3MnO3\n               (LSMO)/PbZr0.2Ti0.8O3 (PZT) heterostructures were built and\n               measured in this article by valence sensitive x-ray absorption\n               spectroscopy. The sizing effects of the heterostructures on the\n               LSMO/PZT magnetoelectric interfaces were investigated through\n               the behavior of Mn valence, a property associated with the LSMO\n               magnetization. We found that Mn valence increases with both LSMO\n               and PZT thickness. Piezoresponse force microscopy revealed a\n               transition from monodomain to polydomain structure along the PZT\n               thickness gradient. The ferroelectric surface charge may change\n               with domain structure and its effects on Mn valence were\n               simulated using a two-orbital double-exchange model. The\n               screening of ferroelectric surface charge increases the electron\n               charges in the interface region, and greatly changes the\n               interfacial Mn valence, which likely plays a leading role in the\n               interfacial magnetoelectric coupling. The LSMO thickness\n               dependence was examined through the combination of two detection\n               modes with drastically different attenuation depths. The\n               different length scales of these techniques' sensitivity to the\n               atomic valence were used to estimate the depth dependence Mn\n               valence. A smaller interfacial Mn valence than the bulk was\n               found by globally fitting the experimental results.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "AIP Publishing",\n  volume    =  107,\n  number    =  14,\n  pages     = "141603",\n  month     =  oct,\n  year      =  2015,\n  keywords  = "LeBeau Group",\n  issn      = "0003-6951",\n  doi       = "10.1063/1.4932517"\n}\n\n
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\n Magnetoelectric materials have great potential to revolutionize electronic devices due to the coupling of their electric and magnetic properties. Thickness varying La0.7Sr0.3MnO3 (LSMO)/PbZr0.2Ti0.8O3 (PZT) heterostructures were built and measured in this article by valence sensitive x-ray absorption spectroscopy. The sizing effects of the heterostructures on the LSMO/PZT magnetoelectric interfaces were investigated through the behavior of Mn valence, a property associated with the LSMO magnetization. We found that Mn valence increases with both LSMO and PZT thickness. Piezoresponse force microscopy revealed a transition from monodomain to polydomain structure along the PZT thickness gradient. The ferroelectric surface charge may change with domain structure and its effects on Mn valence were simulated using a two-orbital double-exchange model. The screening of ferroelectric surface charge increases the electron charges in the interface region, and greatly changes the interfacial Mn valence, which likely plays a leading role in the interfacial magnetoelectric coupling. The LSMO thickness dependence was examined through the combination of two detection modes with drastically different attenuation depths. The different length scales of these techniques' sensitivity to the atomic valence were used to estimate the depth dependence Mn valence. A smaller interfacial Mn valence than the bulk was found by globally fitting the experimental results.\n
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\n \n\n \n \n \n \n \n Imaging magnetic and ferroelectric domains and interfacial spins in magnetoelectric La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$ heterostructures.\n \n \n \n\n\n \n Huang, C., Zhou, J, Tra, V T, White, R, Trappen, R, N'Diaye, A T, Spencer, M, Frye, C, Cabrera, G B, Nguyen, V, LeBeau, J M, Chu, Y., & Holcomb, M B\n\n\n \n\n\n\n J. Phys. Condens. Matter, 27(50): 504003. December 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Huang2015-tp,\n  title     = "Imaging magnetic and ferroelectric domains and interfacial spins\n               in magnetoelectric\n               {La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$}\n               heterostructures",\n  author    = "Huang, C-Y and Zhou, J and Tra, V T and White, R and Trappen, R\n               and N'Diaye, A T and Spencer, M and Frye, C and Cabrera, G B and\n               Nguyen, V and LeBeau, J M and Chu, Y-H and Holcomb, M B",\n  abstract  = "Strong magnetoelectric coupling can occur at the interface\n               between ferromagnetic and ferroelectric films. Similar to work\n               on interfacial exchange bias, photoemission electron microscopy\n               was utilized to image both magnetic and ferroelectric domains\n               and the resulting interfacial Ti spin in the same locations of\n               La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures. Multiple image\n               analysis techniques, which could be applicable for a variety of\n               fields needing quantitative data on image switching, confirm\n               both improved magnetic switching and an increased population of\n               interfacial spins with increased thickness of the ultrathin\n               La0.7Sr0.3MnO3 layer. The perpendicular orientation of the\n               interfacial spins is also discussed. This work suggests a\n               magnetoelectric dead layer, with reduced interfacial\n               magnetoelectricity when thin magnetic films are present.",\n  journal   = "J. Phys. Condens. Matter",\n  publisher = "IOP Publishing",\n  volume    =  27,\n  number    =  50,\n  pages     = "504003",\n  month     =  dec,\n  year      =  2015,\n  keywords  = "LSMO; dichroism; image analysis; interface; magnetoelectric;\n               manganite; photoemission electron microscopy;LeBeau Group",\n  language  = "en",\n  issn      = "0953-8984, 1361-648X",\n  pmid      = "26613406",\n  doi       = "10.1088/0953-8984/27/50/504003"\n}\n\n
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\n Strong magnetoelectric coupling can occur at the interface between ferromagnetic and ferroelectric films. Similar to work on interfacial exchange bias, photoemission electron microscopy was utilized to image both magnetic and ferroelectric domains and the resulting interfacial Ti spin in the same locations of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures. Multiple image analysis techniques, which could be applicable for a variety of fields needing quantitative data on image switching, confirm both improved magnetic switching and an increased population of interfacial spins with increased thickness of the ultrathin La0.7Sr0.3MnO3 layer. The perpendicular orientation of the interfacial spins is also discussed. This work suggests a magnetoelectric dead layer, with reduced interfacial magnetoelectricity when thin magnetic films are present.\n
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\n \n\n \n \n \n \n \n Growth of SrVO$_3$ thin films by hybrid molecular beam epitaxy.\n \n \n \n\n\n \n Eaton, C., Moyer, J. A, Alipour, H. M, Grimley, E. D, Brahlek, M., LeBeau, J. M, & Engel-Herbert, R.\n\n\n \n\n\n\n J. Vac. Sci. Technol. A, 33(6): 061504. November 2015.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Eaton2015-po,\n  title     = "Growth of {SrVO$_3$} thin films by hybrid molecular beam epitaxy",\n  author    = "Eaton, Craig and Moyer, Jarrett A and Alipour, Hamideh M and\n               Grimley, Everett D and Brahlek, Matthew and LeBeau, James M and\n               Engel-Herbert, Roman",\n  abstract  = "The authors report the growth of stoichiometric SrVO3 thin films\n               on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) substrates using hybrid\n               molecular beam epitaxy. This growth approach employs a\n               conventional effusion cell to supply elemental A-site Sr and the\n               metalorganic precursor vanadium oxytriisopropoxide (VTIP) to\n               supply vanadium. Oxygen is supplied in its molecular form\n               through a gas inlet. An optimal VTIP:Sr flux ratio has been\n               identified using reflection high-energy electron-diffraction,\n               x-ray diffraction, atomic force microscopy, and scanning\n               transmission electron microscopy, demonstrating stoichiometric\n               SrVO3 films with atomically flat surface morphology. Away from\n               the optimal VTIP:Sr flux, characteristic changes in the\n               crystalline structure and surface morphology of the films were\n               found, enabling identification of the type of nonstoichiometry.\n               For optimal VTIP:Sr flux ratios, high quality SrVO3 thin films\n               were obtained with smallest deviation of the lattice parameter\n               from the ideal value and with atomically smooth surfaces,\n               indicative of the good cation stoichiometry achieved by this\n               growth technique.",\n  journal   = "J. Vac. Sci. Technol. A",\n  publisher = "American Vacuum Society",\n  volume    =  33,\n  number    =  6,\n  pages     = "061504",\n  month     =  nov,\n  year      =  2015,\n  keywords  = "LeBeau Group;HfO2",\n  issn      = "0734-2101",\n  doi       = "10.1116/1.4927439"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n The authors report the growth of stoichiometric SrVO3 thin films on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) substrates using hybrid molecular beam epitaxy. This growth approach employs a conventional effusion cell to supply elemental A-site Sr and the metalorganic precursor vanadium oxytriisopropoxide (VTIP) to supply vanadium. Oxygen is supplied in its molecular form through a gas inlet. An optimal VTIP:Sr flux ratio has been identified using reflection high-energy electron-diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy, demonstrating stoichiometric SrVO3 films with atomically flat surface morphology. Away from the optimal VTIP:Sr flux, characteristic changes in the crystalline structure and surface morphology of the films were found, enabling identification of the type of nonstoichiometry. For optimal VTIP:Sr flux ratios, high quality SrVO3 thin films were obtained with smallest deviation of the lattice parameter from the ideal value and with atomically smooth surfaces, indicative of the good cation stoichiometry achieved by this growth technique.\n
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\n \n\n \n \n \n \n \n Phase coexistence in Ti$_6$Sn$_5$ intermetallics.\n \n \n \n\n\n \n Oni, A A, Hook, D, Maria, J P, & LeBeau, J M\n\n\n \n\n\n\n Intermetallics, 51: 48–52. August 2014.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Oni2014-um,\n  title    = "Phase coexistence in {Ti$_6$Sn$_5$} intermetallics",\n  author   = "Oni, A A and Hook, D and Maria, J P and LeBeau, J M",\n  abstract = "Here we report the structural characterization of a complex\n              Ti--Sn intermetallic compound, Ti6Sn5. From X-ray diffraction,\n              the resulting compound was observed to exist in both orthorhombic\n              and hexagonal phases. Analysis by electron microscopy revealed\n              that ``planar-like'' defects form throughout the material. Atomic\n              resolution aberration-corrected scanning transmission electron\n              microscopy reveals that these ``planar-like'' defects represent\n              the coexistence of the orthorhombic and hexagonal phases within\n              single grains. The resulting interwoven phases range in thickness\n              from a fraction to multiple unit cells and exhibit coherent phase\n              boundaries with the matrix grain.",\n  journal  = "Intermetallics",\n  volume   =  51,\n  pages    = "48--52",\n  month    =  aug,\n  year     =  2014,\n  keywords = "LeBeau Group;AFOSR - YIP",\n  issn     = "0966-9795",\n  doi      = "10.1016/j.intermet.2014.03.002"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Here we report the structural characterization of a complex Ti–Sn intermetallic compound, Ti6Sn5. From X-ray diffraction, the resulting compound was observed to exist in both orthorhombic and hexagonal phases. Analysis by electron microscopy revealed that ``planar-like'' defects form throughout the material. Atomic resolution aberration-corrected scanning transmission electron microscopy reveals that these ``planar-like'' defects represent the coexistence of the orthorhombic and hexagonal phases within single grains. The resulting interwoven phases range in thickness from a fraction to multiple unit cells and exhibit coherent phase boundaries with the matrix grain.\n
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\n \n\n \n \n \n \n \n The role of terminal oxide structure and properties in nanothermite reactions.\n \n \n \n\n\n \n Mily, E J, Oni, A, LeBeau, J M, Liu, Y, Brown-Shaklee, H J, Ihlefeld, J F, & Maria, J.\n\n\n \n\n\n\n Thin Solid Films, 562: 405–410. July 2014.\n \n\n\n\n
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@ARTICLE{Mily2014-ql,\n  title    = "The role of terminal oxide structure and properties in\n              nanothermite reactions",\n  author   = "Mily, E J and Oni, A and LeBeau, J M and Liu, Y and\n              Brown-Shaklee, H J and Ihlefeld, J F and Maria, J-P",\n  abstract = "In this report, thin films of copper oxide, a common thermite\n              oxidant, and varying metallic species (Al, Zr, and Mg) were\n              deposited in an alternating layered geometry on sapphire by\n              magnetron sputtering. Keeping stoichiometric equivalence, effects\n              of varying metallic constituents were studied with respect to\n              their onset reaction temperature and energy output. Reaction\n              progression was characterized by a systematic step wise vacuum\n              anneal followed by subsequent ex situ x-ray diffraction, and\n              differential thermal analysis. It was found that reaction\n              temperature depends heavily on the terminal oxide's diffusion\n              properties, showing a correlation",\n  journal  = "Thin Solid Films",\n  volume   =  562,\n  pages    = "405--410",\n  month    =  jul,\n  year     =  2014,\n  keywords = "barrier layer; energetic material; film;LeBeau Group;HfO2",\n  issn     = "0040-6090",\n  doi      = "10.1016/j.tsf.2014.05.005"\n}\n\n
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\n In this report, thin films of copper oxide, a common thermite oxidant, and varying metallic species (Al, Zr, and Mg) were deposited in an alternating layered geometry on sapphire by magnetron sputtering. Keeping stoichiometric equivalence, effects of varying metallic constituents were studied with respect to their onset reaction temperature and energy output. Reaction progression was characterized by a systematic step wise vacuum anneal followed by subsequent ex situ x-ray diffraction, and differential thermal analysis. It was found that reaction temperature depends heavily on the terminal oxide's diffusion properties, showing a correlation\n
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\n \n\n \n \n \n \n \n Revolving scanning transmission electron microscopy: Correcting sample drift distortion without prior knowledge.\n \n \n \n\n\n \n Sang, X., & LeBeau, J. M\n\n\n \n\n\n\n Ultramicroscopy, 138: 28–35. March 2014.\n \n\n\n\n
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@ARTICLE{Sang2014-po,\n  title    = "Revolving scanning transmission electron microscopy: Correcting\n              sample drift distortion without prior knowledge",\n  author   = "Sang, Xiahan and LeBeau, James M",\n  abstract = "We report the development of revolving scanning transmission\n              electron microscopy -- RevSTEM -- a technique that enables\n              characterization and removal of sample drift distortion from\n              atomic resolution images without the need for a priori crystal\n              structure information. To measure and correct the distortion, we\n              acquire an image series while rotating the scan coordinate system\n              between successive frames. Through theory and experiment, we show\n              that the revolving image series captures the information\n              necessary to analyze sample drift rate and direction. At atomic\n              resolution, we quantify the image distortion using the projective\n              standard deviation, a rapid, real-space method to directly\n              measure lattice vector angles. By fitting these angles to a\n              physical model, we show that the refined drift parameters provide\n              the input needed to correct distortion across the series. We\n              demonstrate that RevSTEM simultaneously removes the need for a\n              priori structure information to correct distortion, leads to a\n              dramatically improved signal-to-noise ratio, and enables\n              picometer precision and accuracy regardless of drift rate.",\n  journal  = "Ultramicroscopy",\n  volume   =  138,\n  pages    = "28--35",\n  month    =  mar,\n  year     =  2014,\n  keywords = "Drift correction; Image distortion; Projective standard deviation\n              (PSD); Revolving STEM (RevSTEM); Scanning transmission electron\n              microscopy (STEM); Signal to noise ratio;LeBeau\n              Group;QSTEMChapter;Distances;Electron diffuse scattering;HfO2;HEA\n              DMREF;Amazon",\n  language = "en",\n  issn     = "0304-3991, 1879-2723",\n  pmid     = "24444498",\n  doi      = "10.1016/j.ultramic.2013.12.004"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n We report the development of revolving scanning transmission electron microscopy – RevSTEM – a technique that enables characterization and removal of sample drift distortion from atomic resolution images without the need for a priori crystal structure information. To measure and correct the distortion, we acquire an image series while rotating the scan coordinate system between successive frames. Through theory and experiment, we show that the revolving image series captures the information necessary to analyze sample drift rate and direction. At atomic resolution, we quantify the image distortion using the projective standard deviation, a rapid, real-space method to directly measure lattice vector angles. By fitting these angles to a physical model, we show that the refined drift parameters provide the input needed to correct distortion across the series. We demonstrate that RevSTEM simultaneously removes the need for a priori structure information to correct distortion, leads to a dramatically improved signal-to-noise ratio, and enables picometer precision and accuracy regardless of drift rate.\n
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\n \n\n \n \n \n \n \n Smooth cubic commensurate oxides on gallium nitride.\n \n \n \n\n\n \n Paisley, E. A, Gaddy, B. E, LeBeau, J. M, Shelton, C. T, Biegalski, M. D, Christen, H. M, Losego, M. D, Mita, S., Collazo, R., Sitar, Z., Irving, D. L, & Maria, J.\n\n\n \n\n\n\n J. Appl. Phys., 115(6): 064101. February 2014.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Paisley2014-qf,\n  title     = "Smooth cubic commensurate oxides on gallium nitride",\n  author    = "Paisley, Elizabeth A and Gaddy, Benjamin E and LeBeau, James M\n               and Shelton, Christopher T and Biegalski, Michael D and\n               Christen, Hans M and Losego, Mark D and Mita, Seiji and Collazo,\n               Ram{\\'o}n and Sitar, Zlatko and Irving, Douglas L and Maria,\n               Jon-Paul",\n  abstract  = "Smooth, commensurate alloys of ?111?-oriented Mg0.52Ca0.48O\n               (MCO) thin films are demonstrated on Ga-polar, c+\n               [0001]-oriented GaN by surfactant-assisted molecular beam\n               epitaxy and pulsed laser deposition. These are unique examples\n               of coherent cubic oxide|nitride interfaces with structural and\n               morphological perfection. Metal-insulator-semiconductor\n               capacitor structures were fabricated on n-type GaN. A comparison\n               of leakage current density for conventional and\n               surfactant-assisted growth reveals a nearly 100? reduction in\n               leakage current density for the surfactant-assisted samples.\n               HAADF-STEM images of the MCO|GaN interface show commensurate\n               alignment of atomic planes with minimal defects due to lattice\n               mismatch. STEM and DFT calculations show that GaN c/2 steps\n               create incoherent boundaries in MCO over layers which manifest\n               as two in-plane rotations and determine consequently the density\n               of structural defects in otherwise coherent MCO. This new\n               understanding of interfacial steps between HCP and FCC crystals\n               identifies the steps needed to create globally defect-free\n               heterostructures.",\n  journal   = "J. Appl. Phys.",\n  publisher = "American Institute of Physics",\n  volume    =  115,\n  number    =  6,\n  pages     = "064101",\n  month     =  feb,\n  year      =  2014,\n  keywords  = "LeBeau Group;HfO2",\n  issn      = "0021-8979",\n  doi       = "10.1063/1.4861172"\n}\n\n
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\n Smooth, commensurate alloys of ?111?-oriented Mg0.52Ca0.48O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100? reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.\n
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\n \n\n \n \n \n \n \n Ferroelectric phenomena in Si-doped HfO$_2$ thin films with TiN and Ir electrodes.\n \n \n \n\n\n \n Lomenzo, P. D, Zhao, P., Takmeel, Q., Moghaddam, S., Nishida, T., Nelson, M., Fancher, C. M, Grimley, E. D, Sang, X., LeBeau, J. M, & Jones, J. L\n\n\n \n\n\n\n J. Vac. Sci. Technol. B Microelectron. Nanometer Struct. Process. Meas. Phenom., 32(3): 03D123. May 2014.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Lomenzo2014-nn,\n  title     = "Ferroelectric phenomena in {Si}-doped {HfO$_2$} thin films with\n               {TiN} and {Ir} electrodes",\n  author    = "Lomenzo, Patrick D and Zhao, Peng and Takmeel, Qanit and\n               Moghaddam, Saeed and Nishida, Toshikazu and Nelson, Matthew and\n               Fancher, Chris M and Grimley, Everett D and Sang, Xiahan and\n               LeBeau, James M and Jones, Jacob L",\n  abstract  = "Ferroelectric HfO2 is an attractive candidate for future\n               ferroelectric random access memory devices due to its\n               compatibility with the complementary metal-oxide-semiconductor\n               process, conformal deposition, and scaling ability.\n               Crystallization of HfO2 with different dopants and annealing\n               conditions can produce the stabilization of the monoclinic,\n               tetragonal, cubic, or orthorhombic crystal phases. In this work,\n               the authors observe ferroelectric behavior in Si-doped hafnium\n               oxide with TiN and Ir electrodes. Atomic layer deposited 10 nm\n               HfO2 capacitors doped with varying concentrations of SiO2 have\n               been fabricated in the\n               metal--ferroelectric--insulator--semiconductor (MFIS) structure.\n               The ferroelectric characteristics of thin film HfO2 are compared\n               in the MFIS and metal--ferroelectric--metal configurations.\n               Post-metallization anneals were applied to all thin film\n               ferroelectric HfO2 capacitors, resulting in a remanent\n               polarization of up to 22 $\\mu$C/cm2 and a range of observed\n               coercive voltages, emphasizing the importance of the annealing\n               conditions, electrode materials, and device structure on the\n               ferroelectric properties of thin film HfO2.",\n  journal   = "J. Vac. Sci. Technol. B Microelectron. Nanometer Struct.\n               Process. Meas. Phenom.",\n  publisher = "AVS: Science \\& Technology of Materials, Interfaces, and\n               Processing",\n  volume    =  32,\n  number    =  3,\n  pages     = "03D123",\n  month     =  may,\n  year      =  2014,\n  keywords  = "LeBeau Group",\n  issn      = "1071-1023, 2166-2746",\n  doi       = "10.1116/1.4873323"\n}\n\n
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\n Ferroelectric HfO2 is an attractive candidate for future ferroelectric random access memory devices due to its compatibility with the complementary metal-oxide-semiconductor process, conformal deposition, and scaling ability. Crystallization of HfO2 with different dopants and annealing conditions can produce the stabilization of the monoclinic, tetragonal, cubic, or orthorhombic crystal phases. In this work, the authors observe ferroelectric behavior in Si-doped hafnium oxide with TiN and Ir electrodes. Atomic layer deposited 10 nm HfO2 capacitors doped with varying concentrations of SiO2 have been fabricated in the metal–ferroelectric–insulator–semiconductor (MFIS) structure. The ferroelectric characteristics of thin film HfO2 are compared in the MFIS and metal–ferroelectric–metal configurations. Post-metallization anneals were applied to all thin film ferroelectric HfO2 capacitors, resulting in a remanent polarization of up to 22 $μ$C/cm2 and a range of observed coercive voltages, emphasizing the importance of the annealing conditions, electrode materials, and device structure on the ferroelectric properties of thin film HfO2.\n
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\n \n\n \n \n \n \n \n Response of nanostructured ferritic alloys to high-dose heavy ion irradiation.\n \n \n \n\n\n \n Parish, C. M, White, R. M, LeBeau, J. M, & Miller, M. K\n\n\n \n\n\n\n J. Nucl. Mater., 445(1): 251–260. 2014.\n \n\n\n\n
\n\n\n\n \n\n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Parish2014-dx,\n  title    = "Response of nanostructured ferritic alloys to high-dose heavy ion\n              irradiation",\n  author   = "Parish, Chad M and White, Ryan M and LeBeau, James M and Miller,\n              Michael K",\n  abstract = "A latest-generation aberration-corrected scanning/transmission\n              electron microscope (STEM) is used to study heavy-ion-irradiated\n              nanostructured ferritic alloys (NFAs). Results are presented for\n              STEM X-ray mapping of NFA 14YWT irradiated with 10MeV Pt to 16 or\n              160 dpa at −100°C and 750°C, as well as pre-irradiation reference\n              material. Irradiation at −100°C results in ballistic destruction\n              of the beneficial microstructural features present in the\n              pre-irradiated reference material, such as Ti--Y--O nanoclusters\n              (NCs) and grain boundary (GB) segregation. Irradiation at 750°C\n              retains these beneficial features, but indicates some coarsening\n              of the NCs, diffusion of Al to the NCs, and a reduction of the\n              Cr--WGB segregation (or solute excess) content. Ion irradiation\n              combined with the latest-generation STEM hardware allows for\n              rapid screening of fusion candidate materials and improved\n              understanding of irradiation-induced microstructural changes in\n              NFAs.",\n  journal  = "J. Nucl. Mater.",\n  volume   =  445,\n  number   =  1,\n  pages    = "251--260",\n  year     =  2014,\n  keywords = "LeBeau Group;HfO2",\n  issn     = "0022-3115"\n}\n
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\n A latest-generation aberration-corrected scanning/transmission electron microscope (STEM) is used to study heavy-ion-irradiated nanostructured ferritic alloys (NFAs). Results are presented for STEM X-ray mapping of NFA 14YWT irradiated with 10MeV Pt to 16 or 160 dpa at −100°C and 750°C, as well as pre-irradiation reference material. Irradiation at −100°C results in ballistic destruction of the beneficial microstructural features present in the pre-irradiated reference material, such as Ti–Y–O nanoclusters (NCs) and grain boundary (GB) segregation. Irradiation at 750°C retains these beneficial features, but indicates some coarsening of the NCs, diffusion of Al to the NCs, and a reduction of the Cr–WGB segregation (or solute excess) content. Ion irradiation combined with the latest-generation STEM hardware allows for rapid screening of fusion candidate materials and improved understanding of irradiation-induced microstructural changes in NFAs.\n
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\n \n\n \n \n \n \n \n Detector non-uniformity in scanning transmission electron microscopy.\n \n \n \n\n\n \n Findlay, S D, & LeBeau, J M\n\n\n \n\n\n\n Ultramicroscopy, 124: 52–60. January 2013.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Findlay2013-pg,\n  title    = "Detector non-uniformity in scanning transmission electron\n              microscopy",\n  author   = "Findlay, S D and LeBeau, J M",\n  abstract = "A non-uniform response across scanning transmission electron\n              microscope annular detectors has been found experimentally, but\n              is seldom incorporated into simulations. Through case study\n              simulations, we establish the nature and scale of the\n              discrepancies which may arise from failing to account for\n              detector non-uniformity. If standard detectors are used at long\n              camera lengths such that the detector is within or near to the\n              bright field region, we find errors in contrast of the order of\n              10\\%, sufficiently small for qualitative work but non-trivial as\n              experiments become more quantitative. In cases where the detector\n              has been characterized in advance, we discuss the detector\n              response normalization and how it may be incorporated in\n              simulations. \\copyright{} 2012 Elsevier B.V.",\n  journal  = "Ultramicroscopy",\n  volume   =  124,\n  pages    = "52--60",\n  month    =  jan,\n  year     =  2013,\n  keywords = "Detector efficiency.; High-angle annular dark field (HAADF);\n              Scanning transmission electron microscopy (STEM);Detector\n              efficiency;High-angle annular dark field (HAADF);Scanning\n              transmission electron microscopy\n              (STEM);adf-stem;contrast;corrected stem;crystal;dark-field\n              images;probe;thermal diffuse-scattering;thickness;LeBeau\n              Group;QSTEMChapter;Detector;HfO2;3.34",\n  language = "English",\n  issn     = "0304-3991, 1879-2723",\n  pmid     = "23142745",\n  doi      = "10.1016/j.ultramic.2012.09.001"\n}\n\n
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\n A non-uniform response across scanning transmission electron microscope annular detectors has been found experimentally, but is seldom incorporated into simulations. Through case study simulations, we establish the nature and scale of the discrepancies which may arise from failing to account for detector non-uniformity. If standard detectors are used at long camera lengths such that the detector is within or near to the bright field region, we find errors in contrast of the order of 10%, sufficiently small for qualitative work but non-trivial as experiments become more quantitative. In cases where the detector has been characterized in advance, we discuss the detector response normalization and how it may be incorporated in simulations. © 2012 Elsevier B.V.\n
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\n \n\n \n \n \n \n \n Airbrushed nickel nanoparticles for large-area growth of vertically aligned carbon nanofibers on metal (Al, Cu, Ti) surfaces.\n \n \n \n\n\n \n Sarac, M. F, Anderson, B. D, Pearce, R. C, Railsback, J. G, Oni, A. A, White, R. M, Hensley, D. K, LeBeau, J. M, Melechko, A. V, & Tracy, J. B\n\n\n \n\n\n\n ACS Appl. Mater. Interfaces, 5(18): 8955–8960. September 2013.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Sarac2013-pz,\n  title     = "Airbrushed nickel nanoparticles for large-area growth of\n               vertically aligned carbon nanofibers on metal ({Al, Cu, Ti})\n               surfaces",\n  author    = "Sarac, Mehmet F and Anderson, Bryan D and Pearce, Ryan C and\n               Railsback, Justin G and Oni, Adedapo A and White, Ryan M and\n               Hensley, Dale K and LeBeau, James M and Melechko, Anatoli V and\n               Tracy, Joseph B",\n  abstract  = "Vertically aligned carbon nanofibers (VACNFs) were grown by\n               plasma-enhanced chemical vapor deposition (PECVD) using Ni\n               nanoparticle (NP) catalysts that were deposited by airbrushing\n               onto Si, Al, Cu, and Ti substrates. Airbrushing is a simple\n               method for depositing catalyst NPs over large areas that is\n               compatible with roll-to-roll processing. The distribution and\n               morphology of VACNFs are affected by the airbrushing parameters\n               and the composition of the metal foil. Highly concentrated Ni\n               NPs in heptane give more uniform distributions than pentane and\n               hexanes, resulting in more uniform coverage of VACNFs. For VACNF\n               growth on metal foils, Si micropowder was added as a precursor\n               for Si-enriched coatings formed in situ on the VACNFs that\n               impart mechanical rigidity. Interactions between the catalyst\n               NPs and the metal substrates impart control over the VACNF\n               morphology. Growth of carbon nanostructures on Cu is\n               particularly noteworthy because the miscibility of Ni with Cu\n               poses challenges for VACNF growth, and carbon nanostructures\n               anchored to Cu substrates are desired as anode materials for\n               Li-ion batteries and for thermal interface materials.",\n  journal   = "ACS Appl. Mater. Interfaces",\n  publisher = "American Chemical Society",\n  volume    =  5,\n  number    =  18,\n  pages     = "8955--8960",\n  month     =  sep,\n  year      =  2013,\n  keywords  = "airbrushing; carbon nanofibers; carbon nanotubes; catalyst;\n               copper; metal foils; nanoparticles; nickel;LeBeau Group;HfO2",\n  issn      = "1944-8244",\n  pmid      = "24016419",\n  doi       = "10.1021/am401889t"\n}\n\n% The entry below contains non-ASCII chars that could not be converted\n% to a LaTeX equivalent.\n
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\n Vertically aligned carbon nanofibers (VACNFs) were grown by plasma-enhanced chemical vapor deposition (PECVD) using Ni nanoparticle (NP) catalysts that were deposited by airbrushing onto Si, Al, Cu, and Ti substrates. Airbrushing is a simple method for depositing catalyst NPs over large areas that is compatible with roll-to-roll processing. The distribution and morphology of VACNFs are affected by the airbrushing parameters and the composition of the metal foil. Highly concentrated Ni NPs in heptane give more uniform distributions than pentane and hexanes, resulting in more uniform coverage of VACNFs. For VACNF growth on metal foils, Si micropowder was added as a precursor for Si-enriched coatings formed in situ on the VACNFs that impart mechanical rigidity. Interactions between the catalyst NPs and the metal substrates impart control over the VACNF morphology. Growth of carbon nanostructures on Cu is particularly noteworthy because the miscibility of Ni with Cu poses challenges for VACNF growth, and carbon nanostructures anchored to Cu substrates are desired as anode materials for Li-ion batteries and for thermal interface materials.\n
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\n \n\n \n \n \n \n \n From Core–Shell to Alloys: The Preparation and Characterization of Solution-Synthesized AuPd Nanoparticle Catalysts.\n \n \n \n\n\n \n Wilson, A. R, Sun, K., Chi, M., White, R. M, LeBeau, J. M, Lamb, H H., & Wiley, B. J\n\n\n \n\n\n\n J. Phys. Chem. C, 117(34): 17557–17566. August 2013.\n \n\n\n\n
\n\n\n\n \n\n \n \n doi\n  \n \n\n \n link\n  \n \n\n bibtex\n \n\n \n  \n \n abstract \n \n\n \n\n \n \n \n \n \n \n \n\n  \n \n \n \n \n\n\n\n
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@ARTICLE{Wilson2013-kj,\n  title     = "From {Core--Shell} to Alloys: The Preparation and\n               Characterization of {Solution-Synthesized} {AuPd} Nanoparticle\n               Catalysts",\n  author    = "Wilson, Adria R and Sun, Keyi and Chi, Miaofang and White, Ryan\n               M and LeBeau, James M and Lamb, H Henry and Wiley, Benjamin J",\n  abstract  = "This article describes the solution-phase synthesis of 4 nm gold\n               nanoparticles with 0.7 atom-thick, 1.9 atom-thick, and 3.8\n               atom-thick layers of Pd on their surfaces. These well-defined\n               core--shell nanoparticles were deposited on a silica support,\n               calcined, and reduced at 300 °C to create alloyed nanoparticles\n               containing 10.9, 20.2, and 28.5\\% Pd (w/w). Monometallic Pd\n               nanoparticles sintered during calcination at 300 °C, but no\n               sintering was observed for AuPd nanoparticles. Diffuse\n               reflectance infrared Fourier transform (DRIFT) spectra of\n               adsorbed CO suggests that Au donates d electron density to Pd in\n               the core--shell and alloy structures and confirms the presence\n               of Au and Pd atoms on the surface of the nanoparticles after\n               calcination and reduction. The properties of the AuPd alloy\n               catalysts were tested in the vapor-phase conversion of\n               $\\alpha$-limonene to p-cymene. AuPd nanoparticles containing\n               20\\% or more Pd per particle produced p-cymene yields greater\n               than 80\\%, equivalent to conventional Pd catalysts prepared by\n               incipient wetness and ion exchange methods. Very low yields of\n               p-cymene were obtained from dehydrogenation of p-menthane under\n               equivalent conditions, suggesting that the production of\n               p-cymene from $\\alpha$-limonene proceeds through terpinene\n               intermediates.",\n  journal   = "J. Phys. Chem. C",\n  publisher = "American Chemical Society",\n  volume    =  117,\n  number    =  34,\n  pages     = "17557--17566",\n  month     =  aug,\n  year      =  2013,\n  keywords  = "LeBeau Group;HfO2",\n  issn      = "1932-7447",\n  doi       = "10.1021/jp404157m"\n}\n\n
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\n This article describes the solution-phase synthesis of 4 nm gold nanoparticles with 0.7 atom-thick, 1.9 atom-thick, and 3.8 atom-thick layers of Pd on their surfaces. These well-defined core–shell nanoparticles were deposited on a silica support, calcined, and reduced at 300 °C to create alloyed nanoparticles containing 10.9, 20.2, and 28.5% Pd (w/w). Monometallic Pd nanoparticles sintered during calcination at 300 °C, but no sintering was observed for AuPd nanoparticles. Diffuse reflectance infrared Fourier transform (DRIFT) spectra of adsorbed CO suggests that Au donates d electron density to Pd in the core–shell and alloy structures and confirms the presence of Au and Pd atoms on the surface of the nanoparticles after calcination and reduction. The properties of the AuPd alloy catalysts were tested in the vapor-phase conversion of $α$-limonene to p-cymene. AuPd nanoparticles containing 20% or more Pd per particle produced p-cymene yields greater than 80%, equivalent to conventional Pd catalysts prepared by incipient wetness and ion exchange methods. Very low yields of p-cymene were obtained from dehydrogenation of p-menthane under equivalent conditions, suggesting that the production of p-cymene from $α$-limonene proceeds through terpinene intermediates.\n
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\n \n\n \n \n \n \n \n Atomic scale structure and chemistry of Bi2Te3/GaAs interfaces grown by metallorganic van der Waals epitaxy.\n \n \n \n\n\n \n Houston Dycus, J, White, R. M, Pierce, J. M, Venkatasubramanian, R., & LeBeau, J. M\n\n\n \n\n\n\n Appl. Phys. Lett., 102(8): 081601. February 2013.\n \n\n\n\n
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@ARTICLE{Houston_Dycus2013-ea,\n  title     = "Atomic scale structure and chemistry of {Bi2Te3/GaAs} interfaces\n               grown by metallorganic van der Waals epitaxy",\n  author    = "Houston Dycus, J and White, Ryan M and Pierce, Jonathan M and\n               Venkatasubramanian, Rama and LeBeau, James M",\n  abstract  = "Here, we report the atomic scale structure and chemistry of\n               epitaxial Bi2Te3 thin films grown via metallorganic chemical\n               vapor deposition on (001) GaAs substrates. Using aberration\n               corrected high-angle annular dark-field scanning transmission\n               electron microscopy (HAADF STEM), we report an atomically abrupt\n               interface spanned by a second phase. Further, we demonstrate\n               that interpretation of HAADF STEM image intensities does not\n               provide an unambiguous interface structure. Combining atomic\n               resolution imaging and spectroscopy, we determine the identity\n               of the interfacial species is found to be consistent with that\n               of a bilayer of Ga?Te that terminates GaAs dangling bonds.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "American Institute of Physics",\n  volume    =  102,\n  number    =  8,\n  pages     = "081601",\n  month     =  feb,\n  year      =  2013,\n  keywords  = "6835Ct; 6847Fg; 6855ag; 7155Eq; 8115Gh; 8115Kk; III-V\n               semiconductors; MOCVD; bismuth compounds; dangling bonds;\n               gallium arsenide; interface structure; scanning-transmission\n               electron microscopy; semiconductor epitaxial layers;\n               semiconductor growth; semiconductor materials; vapour phase\n               epitaxial growth;LeBeau Group;HfO2",\n  issn      = "0003-6951",\n  doi       = "10.1063/1.4793518"\n}\n\n
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\n Here, we report the atomic scale structure and chemistry of epitaxial Bi2Te3 thin films grown via metallorganic chemical vapor deposition on (001) GaAs substrates. Using aberration corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM), we report an atomically abrupt interface spanned by a second phase. Further, we demonstrate that interpretation of HAADF STEM image intensities does not provide an unambiguous interface structure. Combining atomic resolution imaging and spectroscopy, we determine the identity of the interfacial species is found to be consistent with that of a bilayer of Ga?Te that terminates GaAs dangling bonds.\n
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\n \n\n \n \n \n \n \n Interface properties of Ga(As,P)/(In,Ga)As strained multiple quantum well structures.\n \n \n \n\n\n \n Samberg, J. P, Alipour, H. M, Bradshaw, G. K, Zachary Carlin, C, Colter, P. C, LeBeau, J. M, El-Masry, N A, & Bedair, S. M\n\n\n \n\n\n\n Appl. Phys. Lett., 103(7): 071605. August 2013.\n \n\n\n\n
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@ARTICLE{Samberg2013-fl,\n  title     = "Interface properties of {Ga(As,P)/(In,Ga)As} strained multiple\n               quantum well structures",\n  author    = "Samberg, Joshua P and Alipour, Hamideh M and Bradshaw, Geoffrey\n               K and Zachary Carlin, C and Colter, Peter C and LeBeau, James M\n               and El-Masry, N A and Bedair, Salah M",\n  abstract  = "(In,Ga)As/Ga(As,P) multiple quantum wells (MQWs) with GaAs\n               interface layers have been characterized with photoluminescence\n               (PL) and high resolution scanning transmission electron\n               microscopy (STEM). By growing (In,Ga)As/Ga(As,P) MQWs with\n               asymmetric GaAs interfacial layers, we found that phosphorus\n               carry-over had a profound effect on the absorption edge of the\n               (In,Ga)As wells. Evidence for this phosphorus was initially\n               determined via PL and then definitively proven through STEM and\n               energy dispersive x-ray spectroscopy. We show that the\n               phosphorus carry-over can be prevented with sufficiently thick\n               GaAs transition layers. Preliminary results for GaAs p-i-n solar\n               cells utilizing the improved MQWs are presented.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "American Institute of Physics",\n  volume    =  103,\n  number    =  7,\n  pages     = "071605",\n  month     =  aug,\n  year      =  2013,\n  keywords  = "LeBeau Group;HfO2",\n  issn      = "0003-6951",\n  doi       = "10.1063/1.4818548"\n}\n\n
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\n (In,Ga)As/Ga(As,P) multiple quantum wells (MQWs) with GaAs interface layers have been characterized with photoluminescence (PL) and high resolution scanning transmission electron microscopy (STEM). By growing (In,Ga)As/Ga(As,P) MQWs with asymmetric GaAs interfacial layers, we found that phosphorus carry-over had a profound effect on the absorption edge of the (In,Ga)As wells. Evidence for this phosphorus was initially determined via PL and then definitively proven through STEM and energy dispersive x-ray spectroscopy. We show that the phosphorus carry-over can be prevented with sufficiently thick GaAs transition layers. Preliminary results for GaAs p-i-n solar cells utilizing the improved MQWs are presented.\n
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\n \n\n \n \n \n \n \n Carrier concentration modulation by hot pressing pressure in n-type nanostructured Bi(Se)Te alloy.\n \n \n \n\n\n \n Chan, T. E, LeBeau, J. M, Venkatasubramanian, R., Thomas, P., Stuart, J., & Koch, C. C\n\n\n \n\n\n\n Appl. Phys. Lett., 103(14): 144106. October 2013.\n \n\n\n\n
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@ARTICLE{Chan2013-xv,\n  title     = "Carrier concentration modulation by hot pressing pressure in\n               n-type nanostructured {Bi(Se)Te} alloy",\n  author    = "Chan, Tsung-Ta E and LeBeau, James M and Venkatasubramanian,\n               Rama and Thomas, Peter and Stuart, Judy and Koch, Carl C",\n  abstract  = "We demonstrate experimentally that an optimal hot pressing\n               pressure is required for high thermoelectric power factor in\n               different n-type Bi(Se)Te alloys for a given processing\n               temperature. This phenomenon is attributed to the variations in\n               carrier concentration, which changes the Seebeck coefficient and\n               therefore the power factor. The variations could arise from the\n               difference in the concentration of charged antisite defects as\n               their formation energy changes with pressures. Furthermore,\n               modifications of the energy gap resulting from the lattice\n               distortions at high pressure also likely play a role.",\n  journal   = "Appl. Phys. Lett.",\n  publisher = "AIP Publishing",\n  volume    =  103,\n  number    =  14,\n  pages     = "144106",\n  month     =  oct,\n  year      =  2013,\n  keywords  = "LeBeau Group",\n  issn      = "0003-6951",\n  doi       = "10.1063/1.4823801"\n}\n\n
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\n We demonstrate experimentally that an optimal hot pressing pressure is required for high thermoelectric power factor in different n-type Bi(Se)Te alloys for a given processing temperature. This phenomenon is attributed to the variations in carrier concentration, which changes the Seebeck coefficient and therefore the power factor. The variations could arise from the difference in the concentration of charged antisite defects as their formation energy changes with pressures. Furthermore, modifications of the energy gap resulting from the lattice distortions at high pressure also likely play a role.\n
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\n  \n 2012\n \n \n (1)\n \n \n
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\n \n\n \n \n \n \n \n Interface location by depth sectioning using a low-angle annular dark field detector.\n \n \n \n\n\n \n Ruben, G., Cosgriff, E. C, D'Alfonso, A. J, Findlay, S. D, LeBeau, J. M, & Allen, L. J\n\n\n \n\n\n\n Ultramicroscopy, 113: 131–138. February 2012.\n \n\n\n\n
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@ARTICLE{Ruben2012-my,\n  title    = "Interface location by depth sectioning using a low-angle annular\n              dark field detector",\n  author   = "Ruben, Gary and Cosgriff, Eireann C and D'Alfonso, Adrian J and\n              Findlay, Scott D and LeBeau, James M and Allen, Leslie J",\n  abstract = "We investigate the application of a highly convergent\n              aberration-corrected electron probe to the determination of\n              depth-related features of layered heterostructures. By centring\n              the probe upon an atomic column and varying defocus, we obtain a\n              depth-scan of the signal from a low-angle annular dark field\n              (LAADF) detector. Peaks associated with the heterojunctions and\n              crystal surfaces are observed which allow for the sample\n              thickness and heterojunction locations to be determined.\n              Channelling of the electron wave function along atomic columns is\n              shown to play an important role in the production of these peaks,\n              whose presence at all interfaces is shown to rely on a\n              combination of elastic and thermal diffuse scattering signals.\n              \\copyright{} 2011 Elsevier B.V.",\n  journal  = "Ultramicroscopy",\n  volume   =  113,\n  pages    = "131--138",\n  month    =  feb,\n  year     =  2012,\n  keywords = "Depth sectioning; Heterostructure determination; Low-angle\n              annular dark field; Scanning transmission electron\n              microscopy;Depth sectioning;Heterostructure\n              determination;Low-angle annular dark field;Scanning transmission\n              electron microscopy;atoms;bloch wave\n              analysis;contrast;crystals;debye-waller factors;part\n              i;resolution;scattering;stem;transmission\n              electron-microscopy;LeBeau Group;HfO2",\n  language = "English",\n  issn     = "0304-3991",\n  pmid     = "22257596",\n  doi      = "10.1016/j.ultramic.2011.11.002"\n}\n\n
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\n We investigate the application of a highly convergent aberration-corrected electron probe to the determination of depth-related features of layered heterostructures. By centring the probe upon an atomic column and varying defocus, we obtain a depth-scan of the signal from a low-angle annular dark field (LAADF) detector. Peaks associated with the heterojunctions and crystal surfaces are observed which allow for the sample thickness and heterojunction locations to be determined. Channelling of the electron wave function along atomic columns is shown to play an important role in the production of these peaks, whose presence at all interfaces is shown to rely on a combination of elastic and thermal diffuse scattering signals. © 2011 Elsevier B.V.\n
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\n  \n 2011\n \n \n (1)\n \n \n
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\n \n\n \n \n \n \n \n On the strain in n-type GaN.\n \n \n \n\n\n \n Xie, J., Mita, S., Hussey, L., Rice, A., Tweedie, J., Lebeau, J. M, Collazo, R. R., & Sitar, Z.\n\n\n \n\n\n\n Appl. Phys. Lett., 99(14): 2009–2012. October 2011.\n \n\n\n\n
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@ARTICLE{Xie2011-my,\n  title    = "On the strain in n-type {GaN}",\n  author   = "Xie, Jinqiao and Mita, Seiji and Hussey, Lindsay and Rice,\n              Anthony and Tweedie, James and Lebeau, James M and Collazo,\n              Ramón Ram??n and Sitar, Zlatko",\n  abstract = "It was demonstrated that Ge has the same effect as Si on the\n              strain evolution in n-type GaN as measured by x-ray\n              diffraction.Dislocation inclination, which causes tensile strain\n              in n-type GaN, was clearly observed by transmission electron\n              microscopy where Gedoping was introduced during epitaxialgrowth.\n              This result is explained by the Fermi level effect model that\n              indicates dislocation inclination due to the climbing process\n              through Ga vacancies. Therefore, there is no dependence of\n              dislocation inclination on dopant species.",\n  journal  = "Appl. Phys. Lett.",\n  volume   =  99,\n  number   =  14,\n  pages    = "2009--2012",\n  month    =  oct,\n  year     =  2011,\n  keywords = "Fermi level;III-V semiconductors;Si-doped GaN;X-ray\n              diffraction;aln;dislocation climb;elemental\n              semiconductors;gallium\n              compounds;germanium;impurities;layers;mocvd;photoluminescence;semiconductor\n              doping;semiconductor epitaxial layers;stress;tensile\n              strength;thin-films;transmission electron microscopy;vacancies\n              (crystal);vapour phase epitaxial growth;wide band gap\n              semiconductors;LeBeau Group",\n  language = "English",\n  issn     = "0003-6951",\n  doi      = "10.1063/1.3647772"\n}\n\n
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\n It was demonstrated that Ge has the same effect as Si on the strain evolution in n-type GaN as measured by x-ray diffraction.Dislocation inclination, which causes tensile strain in n-type GaN, was clearly observed by transmission electron microscopy where Gedoping was introduced during epitaxialgrowth. This result is explained by the Fermi level effect model that indicates dislocation inclination due to the climbing process through Ga vacancies. Therefore, there is no dependence of dislocation inclination on dopant species.\n
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