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\n\n \n \n 2024\n \n \n (6)\n \n \n
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\n \n \n\n \n \n \n \n \n \n Diffuse electron scattering reveals kinetic frustration as origin of order in CoCrNi medium entropy alloy.\n \n \n \n \n\n\n \n Foley, D. L.; Barnett, A. K.; Rakita, Y.; Perez, A.; Das, P. P.; Nicolopoulos, S.; Spearot, D. E.; Beyerlein, I. J.; Falk, M. L.; and Taheri, M. L.\n\n\n \n\n\n\n Acta Materialia, 268: 119753. April 2024.\n \n\n\n\n
\n\n\n\n \n \n![\"Diffuse](\"//bibbase.org/img/filetypes/link.svg\"\n\t "\\"Paper\\"\n\t")
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\n\n\n@article{foley_diffuse_2024,\n\ttitle = {Diffuse electron scattering reveals kinetic frustration as origin of order in {CoCrNi} medium entropy alloy},\n\tvolume = {268},\n\tissn = {1359-6454},\n\turl = {https://www.sciencedirect.com/science/article/pii/S135964542400106X},\n\tdoi = {10.1016/j.actamat.2024.119753},\n\tabstract = {Equimolar CoCrNi is driven towards a long-range structure with transformation characteristics similar to that of a strain glass alloy due to the specific stoichiometry and applied aging conditions. This work illustrates the frustrated and kinetically arrested state of this alloy, which develops nano-size, single-phase, isostructural ordered domains at temperatures above 1273 K within a matrix of solid solution. Upon aging at lower temperatures, both atomistic simulation and TEM investigation demonstrate the chemical sensitivity of the matrix by localized symmetry changes which suppress any long-range transformation, mirroring the kinetics observed in strain-glass alloys. Careful quantification of experimental and simulated diffraction patterns from various aging conditions reveal the degree of order in CoCrNi to increase given longer aging times, with achievement of longer domain length scales only when subjected to temperatures below 873 K. This evidence indicates a kinetically constrained, chemically sensitive transition from a disordered fcc to a partially ordered, lower symmetry structure given adequate aging time and temperature. Magnetic effects on the transformation are dictated on the specific alloy stoichiometry and aging temperature, which act to amplify any effects of the glassy kinetics.},\n\turldate = {2024-03-08},\n\tjournal = {Acta Materialia},\n\tauthor = {Foley, Daniel L. and Barnett, Annie K. and Rakita, Yevgeny and Perez, Alejandro and Das, Partha Pratim and Nicolopoulos, Stavros and Spearot, Douglas E. and Beyerlein, Irene J. and Falk, Michael L. and Taheri, Mitra L.},\n\tmonth = apr,\n\tyear = {2024},\n\tkeywords = {Monte Carlo, Transmission electron microscopy, Atomistic simulation, Metal and alloys, Order},\n\tpages = {119753},\n\tfile = {ScienceDirect Snapshot:/Users/yevgenyr/Zotero/storage/4EIMVKRB/S135964542400106X.html:text/html},\n}\n\n\n\n Equimolar CoCrNi is driven towards a long-range structure with transformation characteristics similar to that of a strain glass alloy due to the specific stoichiometry and applied aging conditions. This work illustrates the frustrated and kinetically arrested state of this alloy, which develops nano-size, single-phase, isostructural ordered domains at temperatures above 1273 K within a matrix of solid solution. Upon aging at lower temperatures, both atomistic simulation and TEM investigation demonstrate the chemical sensitivity of the matrix by localized symmetry changes which suppress any long-range transformation, mirroring the kinetics observed in strain-glass alloys. Careful quantification of experimental and simulated diffraction patterns from various aging conditions reveal the degree of order in CoCrNi to increase given longer aging times, with achievement of longer domain length scales only when subjected to temperatures below 873 K. This evidence indicates a kinetically constrained, chemically sensitive transition from a disordered fcc to a partially ordered, lower symmetry structure given adequate aging time and temperature. Magnetic effects on the transformation are dictated on the specific alloy stoichiometry and aging temperature, which act to amplify any effects of the glassy kinetics.\n
\n\n\n\n \n\n \n \n \n \n \n \n Stretched non-negative matrix factorization.\n \n \n \n \n\n\n \n Gu, R.; Rakita, Y.; Lan, L.; Thatcher, Z.; Kamm, G. E.; O’Nolan, D.; Mcbride, B.; Wustrow, A.; Neilson, J. R.; Chapman, K. W.; Du, Q.; and Billinge, S. J. L.\n\n\n \n\n\n\n npj Computational Materials, 10(1): 1–15. August 2024.\n Publisher: Nature Publishing Group\n\n\n\n
\n\n\n\n \n \nPaper\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\n
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\n\n\n@article{gu_stretched_2024,\n\ttitle = {Stretched non-negative matrix factorization},\n\tvolume = {10},\n\tcopyright = {2024 The Author(s)},\n\tissn = {2057-3960},\n\turl = {https://www.nature.com/articles/s41524-024-01377-5},\n\tdoi = {10.1038/s41524-024-01377-5},\n\tabstract = {A novel algorithm, stretchedNMF, is introduced for non-negative matrix factorization (NMF), accounting for signal stretching along the independent variable’s axis. It addresses signal variability caused by stretching, proving beneficial for analyzing data such as powder diffraction at varying temperatures. This approach provides a more meaningful decomposition, particularly when the component signals resemble those from chemical components in the sample. The stretchedNMF model introduces a stretching factor to accommodate signal expansion, solved using discretization and Block Coordinate Descent algorithms. Initial experimental results indicate that the stretchedNMF model outperforms conventional NMF for datasets exhibiting such expansion. An enhanced version, sparse-stretchedNMF, optimized for powder diffraction data from crystalline materials, leverages signal sparsity for accurate extraction, especially with small stretches. Experimental results showcase its effectiveness in analyzing diffraction data, including success in real-time chemical reaction experiments.},\n\tlanguage = {en},\n\tnumber = {1},\n\turldate = {2024-10-10},\n\tjournal = {npj Computational Materials},\n\tauthor = {Gu, Ran and Rakita, Yevgeny and Lan, Ling and Thatcher, Zach and Kamm, Gabrielle E. and O’Nolan, Daniel and Mcbride, Brennan and Wustrow, Allison and Neilson, James R. and Chapman, Karena W. and Du, Qiang and Billinge, Simon J. L.},\n\tmonth = aug,\n\tyear = {2024},\n\tnote = {Publisher: Nature Publishing Group},\n\tkeywords = {Theory and computation, Computational methods},\n\tpages = {1--15},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/UUG7CH3U/Gu et al. - 2024 - Stretched non-negative matrix factorization.pdf:application/pdf},\n}\n\n\n\n A novel algorithm, stretchedNMF, is introduced for non-negative matrix factorization (NMF), accounting for signal stretching along the independent variable’s axis. It addresses signal variability caused by stretching, proving beneficial for analyzing data such as powder diffraction at varying temperatures. This approach provides a more meaningful decomposition, particularly when the component signals resemble those from chemical components in the sample. The stretchedNMF model introduces a stretching factor to accommodate signal expansion, solved using discretization and Block Coordinate Descent algorithms. Initial experimental results indicate that the stretchedNMF model outperforms conventional NMF for datasets exhibiting such expansion. An enhanced version, sparse-stretchedNMF, optimized for powder diffraction data from crystalline materials, leverages signal sparsity for accurate extraction, especially with small stretches. Experimental results showcase its effectiveness in analyzing diffraction data, including success in real-time chemical reaction experiments.\n
\n\n\n\n \n\n \n \n \n \n \n \n Study of Heterogeneity across Csx(CH3NH3)1–xPbBr3 Halide Perovskite Crystals with XPS Imaging and Small-Area Spectra.\n \n \n \n \n\n\n \n Kaslasi, H.; Rakita, Y.; Kaplan-Ashiri, I.; Hodes, G.; and Bendikov, T.\n\n\n \n\n\n\n Crystal Growth & Design, 24(15): 6421–6430. August 2024.\n Publisher: American Chemical Society\n\n\n\n
\n\n\n\n \n \nPaper\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
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\n\n\n@article{kaslasi_study_2024,\n\ttitle = {Study of {Heterogeneity} across {Csx}({CH3NH3})1–{xPbBr3} {Halide} {Perovskite} {Crystals} with {XPS} {Imaging} and {Small}-{Area} {Spectra}},\n\tvolume = {24},\n\tissn = {1528-7483},\n\turl = {https://doi.org/10.1021/acs.cgd.4c00676},\n\tdoi = {10.1021/acs.cgd.4c00676},\n\tabstract = {Interest in halide perovskites (HaPs) is motivated by the combination of superior optoelectronic properties, ease of synthesis, and a surprisingly low density of electrically active defects. HaPs possess high chemical sensitivity, especially those having an organic cation at their A position (AMX3). X-ray photoelectron spectroscopy (XPS) is a surface technique with sensitivity that goes down to a single atomic layer and provides unique information that relates the elemental composition with the chemical and electronic states of the elements in the material. Our study focuses on XPS imaging in combination with selected small-area spectra and uses aged (3 years old) solution-grown single crystals of mixed A-cation CsxMA1–xPbBr3 (MA = CH3NH3+) HaPs as a candidate for investigating intracrystal heterogeneity. With XPS, we followed the variations in chemical composition by measuring crystals at different regions down to 50 μm diameter of the samples. By comparing the surface of the crystals with their cross-section, we found significant changes in the Cs+ and Br– concentrations, which increase toward the interior of the crystal. Contrarily, concentrations of carbon and nitrogen predominate on the top surface and especially at crystal edges, which form a partial covering of the crystals beyond the visible crystal boundaries, something that is not seen by electron microscopy analysis and shows the advantage of the XPS for measurements of light elements. Besides demonstrating the utility of the XPS technique, this compositional heterogeneity within the CsxMA1–xPbBr3 crystals reveals novel insights into the complex chemical nature of what may be seen as uniform single crystals and brings crucial information for their understanding.},\n\tnumber = {15},\n\turldate = {2024-10-10},\n\tjournal = {Crystal Growth \\& Design},\n\tauthor = {Kaslasi, Hadar and Rakita, Yevgeny and Kaplan-Ashiri, Ifat and Hodes, Gary and Bendikov, Tatyana},\n\tmonth = aug,\n\tyear = {2024},\n\tnote = {Publisher: American Chemical Society},\n\tpages = {6421--6430},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/EZ87PTWR/Kaslasi et al. - 2024 - Study of Heterogeneity across Csx(CH3NH3)1–xPbBr3 .pdf:application/pdf},\n}\n\n\n\n Interest in halide perovskites (HaPs) is motivated by the combination of superior optoelectronic properties, ease of synthesis, and a surprisingly low density of electrically active defects. HaPs possess high chemical sensitivity, especially those having an organic cation at their A position (AMX3). X-ray photoelectron spectroscopy (XPS) is a surface technique with sensitivity that goes down to a single atomic layer and provides unique information that relates the elemental composition with the chemical and electronic states of the elements in the material. Our study focuses on XPS imaging in combination with selected small-area spectra and uses aged (3 years old) solution-grown single crystals of mixed A-cation CsxMA1–xPbBr3 (MA = CH3NH3+) HaPs as a candidate for investigating intracrystal heterogeneity. With XPS, we followed the variations in chemical composition by measuring crystals at different regions down to 50 μm diameter of the samples. By comparing the surface of the crystals with their cross-section, we found significant changes in the Cs+ and Br– concentrations, which increase toward the interior of the crystal. Contrarily, concentrations of carbon and nitrogen predominate on the top surface and especially at crystal edges, which form a partial covering of the crystals beyond the visible crystal boundaries, something that is not seen by electron microscopy analysis and shows the advantage of the XPS for measurements of light elements. Besides demonstrating the utility of the XPS technique, this compositional heterogeneity within the CsxMA1–xPbBr3 crystals reveals novel insights into the complex chemical nature of what may be seen as uniform single crystals and brings crucial information for their understanding.\n
\n\n\n\n \n\n \n \n \n \n \n \n Exceptional hardness in multiprincipal element alloys via hierarchical oxygen heterogeneities.\n \n \n \n \n\n\n \n Beaudry, D. C.; Waters, M. J.; Valentino, G. M.; Foley, D. L.; Anber, E.; Rakita, Y.; Brandenburg, C. J.; Couzinié, J.; Perrière, L.; Aoki, T.; Knipling, K. E.; Callahan, P. G.; Redemann, B. W.; McQueen, T. M.; Opila, E. J.; Rondinelli, J. M.; and Taheri, M. L.\n\n\n \n\n\n\n Science Advances, 10(38): eado9697. September 2024.\n Publisher: American Association for the Advancement of Science\n\n\n\n
\n\n\n\n \n \nPaper\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
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\n\n\n@article{beaudry_exceptional_2024,\n\ttitle = {Exceptional hardness in multiprincipal element alloys via hierarchical oxygen heterogeneities},\n\tvolume = {10},\n\turl = {https://www.science.org/doi/10.1126/sciadv.ado9697},\n\tdoi = {10.1126/sciadv.ado9697},\n\tabstract = {Refractory multiprincipal element alloys (RMPEAs) are potential successors to incumbent high-temperature structural alloys, although efforts to improve oxidation resistance with large additions of passivating elements have led to embrittlement. RMPEAs containing group IV and V elements have a balance of properties including moderate ductility, low density, and the necessary formability. We find that oxidation of group IV-V RMPEAs induces hierarchical heterogeneities, ranging from nanoscale interstitial complexes to tertiary phases. This microstructural hierarchy considerably enhances hardness without indentation cracking, with values ranging between 12.1 and 22.6 GPa from the oxide-adjacent metal to the surface oxides, a 3.7 to 6.8× increase over the interstitial-free alloy. Our fundamental understanding of the oxygen influence on phase formation informs future alloy design to enhance oxidation resistance and obtain exceptional hardness while preserving plasticity.},\n\tnumber = {38},\n\turldate = {2024-10-10},\n\tjournal = {Science Advances},\n\tauthor = {Beaudry, David C. and Waters, Michael J. and Valentino, Gianna M. and Foley, Daniel L. and Anber, Elaf and Rakita, Yevgeny and Brandenburg, Charlie J. and Couzinié, Jean-Philippe and Perrière, Loïc and Aoki, Toshihiro and Knipling, Keith E. and Callahan, Patrick G. and Redemann, Benjamin W.Y. and McQueen, Tyrel M. and Opila, Elizabeth J. and Rondinelli, James M. and Taheri, Mitra L.},\n\tmonth = sep,\n\tyear = {2024},\n\tnote = {Publisher: American Association for the Advancement of Science},\n\tpages = {eado9697},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/JTSF3YMF/Beaudry et al. - 2024 - Exceptional hardness in multiprincipal element all.pdf:application/pdf},\n}\n\n\n\n Refractory multiprincipal element alloys (RMPEAs) are potential successors to incumbent high-temperature structural alloys, although efforts to improve oxidation resistance with large additions of passivating elements have led to embrittlement. RMPEAs containing group IV and V elements have a balance of properties including moderate ductility, low density, and the necessary formability. We find that oxidation of group IV-V RMPEAs induces hierarchical heterogeneities, ranging from nanoscale interstitial complexes to tertiary phases. This microstructural hierarchy considerably enhances hardness without indentation cracking, with values ranging between 12.1 and 22.6 GPa from the oxide-adjacent metal to the surface oxides, a 3.7 to 6.8× increase over the interstitial-free alloy. Our fundamental understanding of the oxygen influence on phase formation informs future alloy design to enhance oxidation resistance and obtain exceptional hardness while preserving plasticity.\n
\n\n\n\n \n\n \n \n \n \n \n \n Prior implantation of hydrogen as a mechanism to delay helium bubbles, blistering, and exfoliation in titanium.\n \n \n \n \n\n\n \n Ilyasafov, S. F.; Maman, N.; Kentsch, U.; Zenou, V. Y.; Vaknin, M.; Rakita, Y.; Zamir, G.; Dahan, I.; and Shneck, R. Z.\n\n\n \n\n\n\n Journal of Nuclear Materials, 594: 155017. June 2024.\n \n\n\n\n
\n\n\n\n \n \nPaper\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 \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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\n\n\n@article{ilyasafov_prior_2024,\n\ttitle = {Prior implantation of hydrogen as a mechanism to delay helium bubbles, blistering, and exfoliation in titanium},\n\tvolume = {594},\n\tissn = {0022-3115},\n\turl = {https://www.sciencedirect.com/science/article/pii/S002231152400120X},\n\tdoi = {10.1016/j.jnucmat.2024.155017},\n\tabstract = {This study explores the delaying of the formation of helium bubbles and blisters in pure titanium by hydrogen pre-implantation. Titanium, implanted with helium (40 KeV, 5 × 1017 ions/cm²), exhibited large bubbles that cause exfoliation after heat treatment, whereas hydrogen pre-implantation inhibited bubble growth at room temperature and reduced the exfoliation after heat treatment. In the samples pre-implanted with hydrogen, we found evidence of helium diffusion delay by: (a) a fourfold reduction in bubble pressure (b) faceted cavities in the samples (c) a smaller increase in titanium lattice parameters (d) a 16-fold reduction in average bubble size and a sixfold reduction in bubble area fraction (e) a more than twofold decrease in exfoliation (f) a tendency toward the formation of larger bubbles as a result of heat treatment. We believe that it is reasonable to assume that the inhibition of helium diffusion between tetrahedral interstitial lattice sites takes place because of the occupation of the intermediate octahedral sites by hydrogen atoms. Evidence for the opposite effect, that is inhibition of the diffusion of hydrogen in the presence of helium, is found in the retention of hydrogen in the specimens at elevated temperatures. This retention allowed the existence of titanium hydride after heat treatment at 680 °C. The present study sheds light on the intricate interplay between hydrogen and helium in titanium, providing insights into mechanisms that can potentially mitigate helium-induced damage in materials.},\n\turldate = {2024-10-10},\n\tjournal = {Journal of Nuclear Materials},\n\tauthor = {Ilyasafov, Svetlana Fink and Maman, Nitzan and Kentsch, Ulrich and Zenou, Victor Y. and Vaknin, Moshe and Rakita, Yevgeny and Zamir, Gabriel and Dahan, Itzhak and Shneck, Roni Z.},\n\tmonth = jun,\n\tyear = {2024},\n\tkeywords = {Irradiation damage, Blisters, Bubble formation, EELS, Helium diffusion, Helium implantation, Nuclear technology, Plasma-facing materials (PFMs), Pre-implantation, Repulsive interactions, Surface exfoliation, Titanium hydride},\n\tpages = {155017},\n}\n\n\n\n This study explores the delaying of the formation of helium bubbles and blisters in pure titanium by hydrogen pre-implantation. Titanium, implanted with helium (40 KeV, 5 × 1017 ions/cm²), exhibited large bubbles that cause exfoliation after heat treatment, whereas hydrogen pre-implantation inhibited bubble growth at room temperature and reduced the exfoliation after heat treatment. In the samples pre-implanted with hydrogen, we found evidence of helium diffusion delay by: (a) a fourfold reduction in bubble pressure (b) faceted cavities in the samples (c) a smaller increase in titanium lattice parameters (d) a 16-fold reduction in average bubble size and a sixfold reduction in bubble area fraction (e) a more than twofold decrease in exfoliation (f) a tendency toward the formation of larger bubbles as a result of heat treatment. We believe that it is reasonable to assume that the inhibition of helium diffusion between tetrahedral interstitial lattice sites takes place because of the occupation of the intermediate octahedral sites by hydrogen atoms. Evidence for the opposite effect, that is inhibition of the diffusion of hydrogen in the presence of helium, is found in the retention of hydrogen in the specimens at elevated temperatures. This retention allowed the existence of titanium hydride after heat treatment at 680 °C. The present study sheds light on the intricate interplay between hydrogen and helium in titanium, providing insights into mechanisms that can potentially mitigate helium-induced damage in materials.\n
\n\n\n\n \n\n \n \n \n \n \n \n Surface Defects Control Bulk Carrier Densities in Polycrystalline Pb-Halide Perovskites.\n \n \n \n \n\n\n \n Cahen, D.; Rakita, Y.; Egger, D. A.; and Kahn, A.\n\n\n \n\n\n\n Advanced Materials, 36(50): 2407098. 2024.\n _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.202407098\n\n\n\n
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\n\n\n@article{cahen_surface_2024,\n\ttitle = {Surface {Defects} {Control} {Bulk} {Carrier} {Densities} in {Polycrystalline} {Pb}-{Halide} {Perovskites}},\n\tvolume = {36},\n\tcopyright = {© 2024 The Author(s). Advanced Materials published by Wiley-VCH GmbH},\n\tissn = {1521-4095},\n\turl = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202407098},\n\tdoi = {10.1002/adma.202407098},\n\tabstract = {The (opto)electronic behavior of semiconductors depends on their (quasi-)free electronic carrier densities. These are regulated by semiconductor doping, i.e., controlled “electronic contamination”. For metal halide perovskites (HaPs), the functional materials in several device types, which already challenge some of the understanding of semiconductor properties, this study shows that doping type, density and properties derived from these, are to a first approximation controlled via their surfaces. This effect, relevant to all semiconductors, and already found for some, is very evident for lead (Pb)-HaPs because of their intrinsically low electrically active bulk and surface defect densities. Volume carrier densities for most polycrystalline Pb-HaP films ({\\textless}1 µm grain diameter) are below those resulting from even {\\textless} 0.1\\% of surface sites being electrically active defects. This implies and is consistent with interfacial defects controlling HaP devices in multi-layered structures with most of the action at the two HaP interfaces. Surface and interface passivation effects on bulk electrical properties are relevant to all semiconductors and are crucial for developing those used today. However, because bulk dopant introduction in HaPs at controlled ppm levels for electronic-relevant carrier densities is so difficult, passivation effects are vastly more critical and dominate, to first approximation, their optoelectronic characteristics in devices.},\n\tlanguage = {en},\n\tnumber = {50},\n\turldate = {2025-05-12},\n\tjournal = {Advanced Materials},\n\tauthor = {Cahen, David and Rakita, Yevgeny and Egger, David A. and Kahn, Antoine},\n\tyear = {2024},\n\tnote = {\\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.202407098},\n\tkeywords = {defect tolerance, halide perovskites, self-healing, surface defects},\n\tpages = {2407098},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/8ZH2DWIK/Cahen et al. - 2024 - Surface Defects Control Bulk Carrier Densities in .pdf:application/pdf;Snapshot:/Users/yevgenyr/Zotero/storage/LJ2PSU7Q/adma.html:text/html},\n}\n\n\n The (opto)electronic behavior of semiconductors depends on their (quasi-)free electronic carrier densities. These are regulated by semiconductor doping, i.e., controlled “electronic contamination”. For metal halide perovskites (HaPs), the functional materials in several device types, which already challenge some of the understanding of semiconductor properties, this study shows that doping type, density and properties derived from these, are to a first approximation controlled via their surfaces. This effect, relevant to all semiconductors, and already found for some, is very evident for lead (Pb)-HaPs because of their intrinsically low electrically active bulk and surface defect densities. Volume carrier densities for most polycrystalline Pb-HaP films (\\textless1 µm grain diameter) are below those resulting from even \\textless 0.1% of surface sites being electrically active defects. This implies and is consistent with interfacial defects controlling HaP devices in multi-layered structures with most of the action at the two HaP interfaces. Surface and interface passivation effects on bulk electrical properties are relevant to all semiconductors and are crucial for developing those used today. However, because bulk dopant introduction in HaPs at controlled ppm levels for electronic-relevant carrier densities is so difficult, passivation effects are vastly more critical and dominate, to first approximation, their optoelectronic characteristics in devices.\n
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\n \n \n\n \n \n \n \n \n \n Mapping structural heterogeneity at the nanoscale with scanning nano-structure electron microscopy (SNEM).\n \n \n \n \n\n\n \n Rakita, Y.; Hart, J. L.; Das, P. P.; Shahrezaei, S.; Foley, D. L.; Mathaudhu, S. N.; Nicolopoulos, S.; Taheri, M. L.; and Billinge, S. J. L.\n\n\n \n\n\n\n Acta Materialia, 242: 118426. January 2023.\n \n\n\n\n
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\n\n\n@article{rakita_mapping_2023,\n\ttitle = {Mapping structural heterogeneity at the nanoscale with scanning nano-structure electron microscopy ({SNEM})},\n\tvolume = {242},\n\tissn = {1359-6454},\n\turl = {https://www.sciencedirect.com/science/article/pii/S1359645422008035},\n\tdoi = {10.1016/j.actamat.2022.118426},\n\tabstract = {Here we explore the use of scanning electron diffraction (also known as 4D-STEM) coupled with electron atomic pair distribution function analysis (ePDF) to understand the local order (structure and chemistry) as a function of position in a complex multicomponent system, a hot rolled, Ni-encapsulated, Zr65Cu17.5Ni10Al7.5 bulk metallic glass (BMG), with a spatial resolution of 3 nm. We show that it is possible to gain insight into the chemistry and chemical clustering/ordering tendency in different regions of the sample, including in the vicinity of nano-scale crystallites that are identified from virtual dark field images and in heavily deformed regions at the edge of the BMG. In addition to simpler analysis, unsupervised machine learning was used to extract partial PDFs from the material, modeled as a quasi-binary alloy, and map them in space. These maps allowed key insights not only into the local average composition, as validated by EELS, but also a unique insight into chemical short-range ordering tendencies in different regions of the sample during formation. The experiments are straightforward and rapid and, unlike spectroscopic measurements, don’t require energy filters on the instrument. We spatially map different quantities of interest (QoI’s), defined as scalars that can be computed directly from positions and widths of ePDF peaks or parameters refined from fits to the patterns. We developed a flexible and rapid data reduction and analysis software framework that allows experimenters to rapidly explore images of the sample on the basis of different QoI’s. The power and flexibility of this approach are explored and described in detail. Because of the fact that we are getting spatially resolved images of the nanoscale structure obtained from ePDFs we call this approach scanning nano-structure electron microscopy (SNEM), and we believe that it will be powerful and useful extension of current 4D-STEM methods.},\n\turldate = {2023-12-13},\n\tjournal = {Acta Materialia},\n\tauthor = {Rakita, Yevgeny and Hart, James L. and Das, Partha Pratim and Shahrezaei, Sina and Foley, Daniel L. and Mathaudhu, Suveen Nigel and Nicolopoulos, Stavros and Taheri, Mitra L. and Billinge, Simon J. L.},\n\tmonth = jan,\n\tyear = {2023},\n\tkeywords = {Pair distribution function, Metallic glass, 4D STEM},\n\tpages = {118426},\n\tfile = {ScienceDirect Snapshot:/Users/yevgenyr/Zotero/storage/5YSPADZ4/S1359645422008035.html:text/html;Submitted Version:/Users/yevgenyr/Zotero/storage/4HDIAPGK/Rakita et al. - 2023 - Mapping structural heterogeneity at the nanoscale .pdf:application/pdf},\n}\n\n\n\n Here we explore the use of scanning electron diffraction (also known as 4D-STEM) coupled with electron atomic pair distribution function analysis (ePDF) to understand the local order (structure and chemistry) as a function of position in a complex multicomponent system, a hot rolled, Ni-encapsulated, Zr65Cu17.5Ni10Al7.5 bulk metallic glass (BMG), with a spatial resolution of 3 nm. We show that it is possible to gain insight into the chemistry and chemical clustering/ordering tendency in different regions of the sample, including in the vicinity of nano-scale crystallites that are identified from virtual dark field images and in heavily deformed regions at the edge of the BMG. In addition to simpler analysis, unsupervised machine learning was used to extract partial PDFs from the material, modeled as a quasi-binary alloy, and map them in space. These maps allowed key insights not only into the local average composition, as validated by EELS, but also a unique insight into chemical short-range ordering tendencies in different regions of the sample during formation. The experiments are straightforward and rapid and, unlike spectroscopic measurements, don’t require energy filters on the instrument. We spatially map different quantities of interest (QoI’s), defined as scalars that can be computed directly from positions and widths of ePDF peaks or parameters refined from fits to the patterns. We developed a flexible and rapid data reduction and analysis software framework that allows experimenters to rapidly explore images of the sample on the basis of different QoI’s. The power and flexibility of this approach are explored and described in detail. Because of the fact that we are getting spatially resolved images of the nanoscale structure obtained from ePDFs we call this approach scanning nano-structure electron microscopy (SNEM), and we believe that it will be powerful and useful extension of current 4D-STEM methods.\n
\n\n\n\n \n\n \n \n \n \n \n \n 10.09 - Local structure determination using total scattering data.\n \n \n \n \n\n\n \n Billinge, S. J. L.; Skjaervoe, S. H.; Terban, M. W.; Tao, S.; Yang, L.; Rakita, Y.; and Frandsen, B. A.\n\n\n \n\n\n\n In Reedijk, J.; and Poeppelmeier, K. R., editor(s), Comprehensive Inorganic Chemistry III (Third Edition), pages 222–247. Elsevier, Oxford, January 2023.\n \n\n\n\n
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\n\n\n@incollection{billinge_1009_2023,\n\taddress = {Oxford},\n\ttitle = {10.09 - {Local} structure determination using total scattering data},\n\tisbn = {978-0-12-823153-1},\n\turl = {https://www.sciencedirect.com/science/article/pii/B9780128231449000406},\n\tabstract = {“This article describes the application of total scattering and atomic pair distribution function (PDF) studies to the study of local and intermediate range structure in complex materials. We give a brief introduction to the methods, and then survey a sampling of different applications of them in various inorganic chemistry applications, including energy materials, nanoparticles, layered materials, metal organic frameworks and host-guest systems, polycrystalline thin films, atomic clusters, hybrid-perovskites. We also discuss studies of local magnetism and amorphous materials.”},\n\turldate = {2023-12-13},\n\tbooktitle = {Comprehensive {Inorganic} {Chemistry} {III} ({Third} {Edition})},\n\tpublisher = {Elsevier},\n\tauthor = {Billinge, Simon J. L. and Skjaervoe, Sandra H. and Terban, Maxwell W. and Tao, Songsheng and Yang, Long and Rakita, Yevgeny and Frandsen, Benjamin A.},\n\teditor = {Reedijk, Jan and Poeppelmeier, Kenneth R.},\n\tmonth = jan,\n\tyear = {2023},\n\tdoi = {10.1016/B978-0-12-823144-9.00040-6},\n\tkeywords = {Total scattering, X-ray diffraction, Nanomaterials, Local structure, Neutron diffraction, PDF, Nanoparticles, Electron diffraction, Atomic pair distribution function analysis},\n\tpages = {222--247},\n\tfile = {ScienceDirect Snapshot:/Users/yevgenyr/Zotero/storage/2N9EIMP4/B9780128231449000406.html:text/html},\n}\n\n\n\n “This article describes the application of total scattering and atomic pair distribution function (PDF) studies to the study of local and intermediate range structure in complex materials. We give a brief introduction to the methods, and then survey a sampling of different applications of them in various inorganic chemistry applications, including energy materials, nanoparticles, layered materials, metal organic frameworks and host-guest systems, polycrystalline thin films, atomic clusters, hybrid-perovskites. We also discuss studies of local magnetism and amorphous materials.”\n
\n\n\n\n \n\n \n \n \n \n \n \n Phonon-driven intra-exciton Rabi oscillations in CsPbBr3 halide perovskites.\n \n \n \n \n\n\n \n Nguyen, X. T.; Winte, K.; Timmer, D.; Rakita, Y.; Ceratti, D. R.; Aharon, S.; Ramzan, M. S.; Cocchi, C.; Lorke, M.; Jahnke, F.; Cahen, D.; Lienau, C.; and De Sio, A.\n\n\n \n\n\n\n Nature Communications, 14(1): 1047. February 2023.\n Number: 1 Publisher: Nature Publishing Group\n\n\n\n
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\n\n\n@article{nguyen_phonon-driven_2023,\n\ttitle = {Phonon-driven intra-exciton {Rabi} oscillations in {CsPbBr3} halide perovskites},\n\tvolume = {14},\n\tcopyright = {2023 The Author(s)},\n\tissn = {2041-1723},\n\turl = {https://www.nature.com/articles/s41467-023-36654-2},\n\tdoi = {10.1038/s41467-023-36654-2},\n\tabstract = {Coupling electromagnetic radiation with matter, e.g., by resonant light fields in external optical cavities, is highly promising for tailoring the optoelectronic properties of functional materials on the nanoscale. Here, we demonstrate that even internal fields induced by coherent lattice motions can be used to control the transient excitonic optical response in CsPbBr3 halide perovskite crystals. Upon resonant photoexcitation, two-dimensional electronic spectroscopy reveals an excitonic peak structure oscillating persistently with a 100-fs period for up to {\\textasciitilde}2 ps which does not match the frequency of any phonon modes of the crystals. Only at later times, beyond 2 ps, two low-frequency phonons of the lead-bromide lattice dominate the dynamics. We rationalize these findings by an unusual exciton-phonon coupling inducing off-resonant 100-fs Rabi oscillations between 1s and 2p excitons driven by the low-frequency phonons. As such, prevailing models for the electron-phonon coupling in halide perovskites are insufficient to explain these results. We propose the coupling of characteristic low-frequency phonon fields to intra-excitonic transitions in halide perovskites as the key to control the anharmonic response of these materials in order to establish new routes for enhancing their optoelectronic properties.},\n\tlanguage = {en},\n\tnumber = {1},\n\turldate = {2023-12-13},\n\tjournal = {Nature Communications},\n\tauthor = {Nguyen, Xuan Trung and Winte, Katrin and Timmer, Daniel and Rakita, Yevgeny and Ceratti, Davide Raffaele and Aharon, Sigalit and Ramzan, Muhammad Sufyan and Cocchi, Caterina and Lorke, Michael and Jahnke, Frank and Cahen, David and Lienau, Christoph and De Sio, Antonietta},\n\tmonth = feb,\n\tyear = {2023},\n\tnote = {Number: 1\nPublisher: Nature Publishing Group},\n\tkeywords = {Condensed-matter physics, Materials for devices, Optical spectroscopy},\n\tpages = {1047},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/WL4MH2GV/Nguyen et al. - 2023 - Phonon-driven intra-exciton Rabi oscillations in C.pdf:application/pdf},\n}\n\n\n\n Coupling electromagnetic radiation with matter, e.g., by resonant light fields in external optical cavities, is highly promising for tailoring the optoelectronic properties of functional materials on the nanoscale. Here, we demonstrate that even internal fields induced by coherent lattice motions can be used to control the transient excitonic optical response in CsPbBr3 halide perovskite crystals. Upon resonant photoexcitation, two-dimensional electronic spectroscopy reveals an excitonic peak structure oscillating persistently with a 100-fs period for up to ~2 ps which does not match the frequency of any phonon modes of the crystals. Only at later times, beyond 2 ps, two low-frequency phonons of the lead-bromide lattice dominate the dynamics. We rationalize these findings by an unusual exciton-phonon coupling inducing off-resonant 100-fs Rabi oscillations between 1s and 2p excitons driven by the low-frequency phonons. As such, prevailing models for the electron-phonon coupling in halide perovskites are insufficient to explain these results. We propose the coupling of characteristic low-frequency phonon fields to intra-excitonic transitions in halide perovskites as the key to control the anharmonic response of these materials in order to establish new routes for enhancing their optoelectronic properties.\n
\n\n\n\n \n\n \n \n \n \n \n \n Thermal Contributions to the Local and Long-Range Structural Disorder in CH3NH3PbBr3.\n \n \n \n \n\n\n \n Weadock, N. J.; MacKeen, C.; Qin, X.; Waquier, L.; Rakita, Y.; Vigil, J. A.; Karunadasa, H. I.; Blum, V.; Toney, M. F.; and Bridges, F.\n\n\n \n\n\n\n PRX Energy, 2(3): 033004. July 2023.\n Publisher: American Physical Society\n\n\n\n
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\n\n\n@article{weadock_thermal_2023,\n\ttitle = {Thermal {Contributions} to the {Local} and {Long}-{Range} {Structural} {Disorder} in {CH3NH3PbBr3}},\n\tvolume = {2},\n\turl = {https://link.aps.org/doi/10.1103/PRXEnergy.2.033004},\n\tdoi = {10.1103/PRXEnergy.2.033004},\n\tabstract = {The hybrid lead halide perovskite (LHP) family exhibits large structural fluctuations that contribute to the remarkable properties of LHP-based optoelectronic devices. In three-dimensional LHPs such as CH3NH3PbBr3, the structural phase transitions have been well characterized; changes in local structure and origins of structural disorder, however, have received less attention. We investigate the temperature dependence of the Pb—Br bond distribution, effective spring constant, and dynamic correlations with a combined extended x-ray-absorption fine structure (EXAFS), single-crystal x-ray diffraction (SXRD) and ab initio molecular dynamics (AIMD) study. EXAFS provides a snapshot of the local environment around the probe atom, rather than the time- and space-averaged structure obtained from SXRD. Molecular librations are observed below the orthorhombic-tetragonal transition temperature, and across this transition we find an anomalous increase in the Pb-Br effective spring constant. The x-ray absorption near edge structure reveals only subtle changes in the electronic structure; therefore, we propose that the increase in bond strength is the result of a redistribution of the charge density, concomitant with the loss of persistent Br…H bonding. Furthermore, the temperature dependence of the Pb—Br bond asymmetry indicates that the structural disorder in CH3NH3PbBr3 is primarily driven by thermally activated anharmonic dynamics rather than static disorder. Our results describe the local structure responsible for the optoelectronic performance of LHP devices and bring new insights into modifying halide bonding to prevent halide migration.},\n\tnumber = {3},\n\turldate = {2023-12-13},\n\tjournal = {PRX Energy},\n\tauthor = {Weadock, Nicholas J. and MacKeen, Cameron and Qin, Xixi and Waquier, Louis and Rakita, Yevgeny and Vigil, Julian A. and Karunadasa, Hemamala I. and Blum, Volker and Toney, Michael F. and Bridges, Frank},\n\tmonth = jul,\n\tyear = {2023},\n\tnote = {Publisher: American Physical Society},\n\tpages = {033004},\n\tfile = {APS Snapshot:/Users/yevgenyr/Zotero/storage/RQE5W6T5/PRXEnergy.2.html:text/html;Full Text PDF:/Users/yevgenyr/Zotero/storage/YELKCPXB/Weadock et al. - 2023 - Thermal Contributions to the Local and Long-Range .pdf:application/pdf},\n}\n\n\n\n The hybrid lead halide perovskite (LHP) family exhibits large structural fluctuations that contribute to the remarkable properties of LHP-based optoelectronic devices. In three-dimensional LHPs such as CH3NH3PbBr3, the structural phase transitions have been well characterized; changes in local structure and origins of structural disorder, however, have received less attention. We investigate the temperature dependence of the Pb—Br bond distribution, effective spring constant, and dynamic correlations with a combined extended x-ray-absorption fine structure (EXAFS), single-crystal x-ray diffraction (SXRD) and ab initio molecular dynamics (AIMD) study. EXAFS provides a snapshot of the local environment around the probe atom, rather than the time- and space-averaged structure obtained from SXRD. Molecular librations are observed below the orthorhombic-tetragonal transition temperature, and across this transition we find an anomalous increase in the Pb-Br effective spring constant. The x-ray absorption near edge structure reveals only subtle changes in the electronic structure; therefore, we propose that the increase in bond strength is the result of a redistribution of the charge density, concomitant with the loss of persistent Br…H bonding. Furthermore, the temperature dependence of the Pb—Br bond asymmetry indicates that the structural disorder in CH3NH3PbBr3 is primarily driven by thermally activated anharmonic dynamics rather than static disorder. Our results describe the local structure responsible for the optoelectronic performance of LHP devices and bring new insights into modifying halide bonding to prevent halide migration.\n
\n\n\n\n \n\n \n \n \n \n \n \n Sacrificial nano-sized carbon-based scaffolds for MAX phase to MXene-based technologies.\n \n \n \n \n\n\n \n Sobolev, K.; and Rakita, Y.\n\n\n \n\n\n\n Matter, 6(8): 2597–2599. August 2023.\n Publisher: Elsevier\n\n\n\n
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\n\n\n\n@article{sobolev_sacrificial_2023,\n\ttitle = {Sacrificial nano-sized carbon-based scaffolds for {MAX} phase to {MXene}-based technologies},\n\tvolume = {6},\n\tissn = {2590-2393, 2590-2385},\n\turl = {https://www.cell.com/matter/abstract/S2590-2385(23)00322-3},\n\tdoi = {10.1016/j.matt.2023.06.037},\n\tlanguage = {English},\n\tnumber = {8},\n\turldate = {2023-12-13},\n\tjournal = {Matter},\n\tauthor = {Sobolev, Kirill and Rakita, Yevgeny},\n\tmonth = aug,\n\tyear = {2023},\n\tnote = {Publisher: Elsevier},\n\tpages = {2597--2599},\n}\n\n\n\n \n\n \n \n \n \n \n \n Stretched Non-negative Matrix Factorization.\n \n \n \n \n\n\n \n Gu, R.; Rakita, Y.; Lan, L.; Thatcher, Z.; Kamm, G. E.; O'Nolan, D.; Mcbride, B.; Wustrow, A.; Neilson, J. R.; Chapman, K. W.; Du, Q.; and Billinge, S. J. L.\n\n\n \n\n\n\n November 2023.\n arXiv:2311.15173 [cond-mat]\n\n\n\n
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\n\n\n@misc{gu_stretched_2023,\n\ttitle = {Stretched {Non}-negative {Matrix} {Factorization}},\n\turl = {http://arxiv.org/abs/2311.15173},\n\tdoi = {10.48550/arXiv.2311.15173},\n\tabstract = {An algorithm is described and tested that carries out a non negative matrix factorization (NMF) ignoring any stretching of the signal along the axis of the independent variable. This extended NMF model is called StretchedNMF. Variability in a set of signals due to this stretching is then ignored in the decomposition. This can be used, for example, to study sets of powder diffraction data collected at different temperatures where the materials are undergoing thermal expansion. It gives a more meaningful decomposition in this case where the component signals resemble signals from chemical components in the sample. The StretchedNMF model introduces a new variable, the stretching factor, to describe any expansion of the signal. To solve StretchedNMF, we discretize it and employ Block Coordinate Descent framework algorithms. The initial experimental results indicate that StretchedNMF model outperforms the conventional NMF for sets of data with such an expansion. A further enhancement to StretchedNMF for the case of powder diffraction data from crystalline materials called Sparse-StretchedNMF, which makes use of the sparsity of the powder diffraction signals, allows correct extractions even for very small stretches where StretchedNMF struggles. As well as demonstrating the model performance on simulated PXRD patterns and atomic pair distribution functions (PDFs), it also proved successful when applied to real data taken from an in situ chemical reaction experiment.},\n\turldate = {2023-12-13},\n\tpublisher = {arXiv},\n\tauthor = {Gu, Ran and Rakita, Yevgeny and Lan, Ling and Thatcher, Zach and Kamm, Gabrielle E. and O'Nolan, Daniel and Mcbride, Brennan and Wustrow, Allison and Neilson, James R. and Chapman, Karena W. and Du, Qiang and Billinge, Simon J. L.},\n\tmonth = nov,\n\tyear = {2023},\n\tnote = {arXiv:2311.15173 [cond-mat]},\n\tkeywords = {Condensed Matter - Materials Science},\n\tfile = {arXiv Fulltext PDF:/Users/yevgenyr/Zotero/storage/B4FNF4UB/Gu et al. - 2023 - Stretched Non-negative Matrix Factorization.pdf:application/pdf;arXiv.org Snapshot:/Users/yevgenyr/Zotero/storage/KHXDDTP5/2311.html:text/html},\n}\n\n\n\n An algorithm is described and tested that carries out a non negative matrix factorization (NMF) ignoring any stretching of the signal along the axis of the independent variable. This extended NMF model is called StretchedNMF. Variability in a set of signals due to this stretching is then ignored in the decomposition. This can be used, for example, to study sets of powder diffraction data collected at different temperatures where the materials are undergoing thermal expansion. It gives a more meaningful decomposition in this case where the component signals resemble signals from chemical components in the sample. The StretchedNMF model introduces a new variable, the stretching factor, to describe any expansion of the signal. To solve StretchedNMF, we discretize it and employ Block Coordinate Descent framework algorithms. The initial experimental results indicate that StretchedNMF model outperforms the conventional NMF for sets of data with such an expansion. A further enhancement to StretchedNMF for the case of powder diffraction data from crystalline materials called Sparse-StretchedNMF, which makes use of the sparsity of the powder diffraction signals, allows correct extractions even for very small stretches where StretchedNMF struggles. As well as demonstrating the model performance on simulated PXRD patterns and atomic pair distribution functions (PDFs), it also proved successful when applied to real data taken from an in situ chemical reaction experiment.\n
\n\n\n\n \n\n \n \n \n \n \n \n Local structure, bonding, and asymmetry of ((NH2)2CH)PbBr3 , CsPbBr3, and (CH3NH3)PbBr.\n \n \n \n \n\n\n \n Bridges, F.; Gruzdas, J.; MacKeen, C.; Mayford, K.; Weadock, N. J.; Baltazar, V. U.; Rakita, Y.; Waquier, L.; Vigil, J. A.; Karunadasa, H. I.; and Toney, M. F.\n\n\n \n\n\n\n Physical Review B, 108(21): 214102. December 2023.\n Publisher: American Physical Society\n\n\n\n
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\n\n\n@article{bridges_local_2023,\n\ttitle = {Local structure, bonding, and asymmetry of (({NH2}){2CH}){PbBr3} , {CsPbBr3}, and ({CH3NH3}){PbBr}},\n\tvolume = {108},\n\turl = {https://link.aps.org/doi/10.1103/PhysRevB.108.214102},\n\tdoi = {10.1103/PhysRevB.108.214102},\n\tabstract = {We report local structure measurements for CsPbBr3 and ((NH2)2CH)PbBr3 (FAPbBr3) and compare them with recent results for (CH3NH3)PbBr3 (MAPbBr3). The Pb-Br bonding is similar for all three systems; the effective spring constants, κ, are comparable (ranging from 1.20 to 1.95 eV/Å2), but small in magnitude indicating very soft materials. However, there are also important differences between the three systems. Static disorder is very small for CsPbBr3 but increases somewhat with the size of the organic molecular ions MA+ and FA+. At room temperature, dynamic disorder dominates in all compounds. The thermal disorder of the Pb-Br pair distribution function (PDF), i.e., the Debye-Waller factor σ2 follows a correlated Debye or Einstein model up to 300 K in CsPbBr3 (orthorhombic phase), but for FAPbBr3 and MAPbBr3, there is a break in the σ2(T) curve at the orthorhombic-tetragonal transition (o-t) near 150 K, indicating a small change in the spring constant κ. κ increases for MAPbBr3 but decreases in FAPbBr3 at this transition. These changes are attributed to changes in the H-bonding between Br− and MA+ or FA+ at this transition, as a result of librations or rotations of these molecular cations. In addition, the Pb-Br PDF becomes asymmetric at a relatively low temperature for FAPbBr3 and MAPbBr3, while this effect is significantly smaller for CsPbBr3. Finally, we address the question of a model to explain the asymmetric PDF. Two main models are discussed in the literature, an anharmonic pair potential and a split-pair distribution, possibly driven by the presence of a lone pair on the Pb ion. We show that the fourth cumulant C4 can differentiate between these two models and other possible models. Experimentally C4 is positive at 250 K and above, for all three systems and that is inconsistent with a split-peak model, for which C4 is negative for splittings larger than 0.12 Å.},\n\tnumber = {21},\n\turldate = {2023-12-13},\n\tjournal = {Physical Review B},\n\tauthor = {Bridges, F. and Gruzdas, J. and MacKeen, C. and Mayford, K. and Weadock, N. J. and Baltazar, V. Urena and Rakita, Y. and Waquier, Louis and Vigil, Julian A. and Karunadasa, Hemamala I. and Toney, M. F.},\n\tmonth = dec,\n\tyear = {2023},\n\tnote = {Publisher: American Physical Society},\n\tpages = {214102},\n\tfile = {APS Snapshot:/Users/yevgenyr/Zotero/storage/P2NGSNQ3/PhysRevB.108.html:text/html;Full Text PDF:/Users/yevgenyr/Zotero/storage/NY54HV73/Bridges et al. - 2023 - Local structure, bonding, and asymmetry of \\$( ( m.pdf:application/pdf},\n}\n\n\n\n We report local structure measurements for CsPbBr3 and ((NH2)2CH)PbBr3 (FAPbBr3) and compare them with recent results for (CH3NH3)PbBr3 (MAPbBr3). The Pb-Br bonding is similar for all three systems; the effective spring constants, κ, are comparable (ranging from 1.20 to 1.95 eV/Å2), but small in magnitude indicating very soft materials. However, there are also important differences between the three systems. Static disorder is very small for CsPbBr3 but increases somewhat with the size of the organic molecular ions MA+ and FA+. At room temperature, dynamic disorder dominates in all compounds. The thermal disorder of the Pb-Br pair distribution function (PDF), i.e., the Debye-Waller factor σ2 follows a correlated Debye or Einstein model up to 300 K in CsPbBr3 (orthorhombic phase), but for FAPbBr3 and MAPbBr3, there is a break in the σ2(T) curve at the orthorhombic-tetragonal transition (o-t) near 150 K, indicating a small change in the spring constant κ. κ increases for MAPbBr3 but decreases in FAPbBr3 at this transition. These changes are attributed to changes in the H-bonding between Br− and MA+ or FA+ at this transition, as a result of librations or rotations of these molecular cations. In addition, the Pb-Br PDF becomes asymmetric at a relatively low temperature for FAPbBr3 and MAPbBr3, while this effect is significantly smaller for CsPbBr3. Finally, we address the question of a model to explain the asymmetric PDF. Two main models are discussed in the literature, an anharmonic pair potential and a split-pair distribution, possibly driven by the presence of a lone pair on the Pb ion. We show that the fourth cumulant C4 can differentiate between these two models and other possible models. Experimentally C4 is positive at 250 K and above, for all three systems and that is inconsistent with a split-peak model, for which C4 is negative for splittings larger than 0.12 Å.\n
\n\n\n\n \n\n \n \n \n \n \n \n Understanding and leveraging short-range order in compositionally complex alloys.\n \n \n \n \n\n\n \n Taheri, M. L.; Anber, E.; Barnett, A.; Billinge, S.; Birbilis, N.; DeCost, B.; Foley, D. L.; Holcombe, E.; Hollenbach, J.; Joress, H.; Leigh, G.; Rakita, Y.; Rondinelli, J. M.; Smith, N.; Waters, M. J.; and Wolverton, C.\n\n\n \n\n\n\n MRS Bulletin, 48(12): 1280–1291. December 2023.\n \n\n\n\n
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\n\n\n@article{taheri_understanding_2023,\n\ttitle = {Understanding and leveraging short-range order in compositionally complex alloys},\n\tvolume = {48},\n\tissn = {1938-1425},\n\turl = {https://doi.org/10.1557/s43577-023-00591-8},\n\tdoi = {10.1557/s43577-023-00591-8},\n\tabstract = {In this article, we review the opportunities and challenges associated with complex concentrated materials that exhibit short-range order. Although the presence of such phenomena has been theorized, accurate computational representation, characterization, and materials design have clear challenges associated with its complexity. Advances in both high-resolution and high-fidelity methods, as well as machine-learning-aided techniques, have paved a path for realization of complex concentrated systems with deterministic short-range order, and provide a foundation on which these alloys and materials can be developed for various applications in functional, structural, and biomedical applications.},\n\tlanguage = {en},\n\tnumber = {12},\n\turldate = {2024-03-08},\n\tjournal = {MRS Bulletin},\n\tauthor = {Taheri, Mitra L. and Anber, Elaf and Barnett, Annie and Billinge, Simon and Birbilis, Nick and DeCost, Brian and Foley, Daniel L. and Holcombe, Emily and Hollenbach, Jonathan and Joress, Howie and Leigh, Georgia and Rakita, Yevgeny and Rondinelli, James M. and Smith, Nathan and Waters, Michael J. and Wolverton, Chris},\n\tmonth = dec,\n\tyear = {2023},\n\tkeywords = {High-entropy alloys, Machine learning, Spectroscopy, Extended x-ray absorption fine structure (EXAFS), Transmission electron microscopy (TEM)},\n\tpages = {1280--1291},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/AWQZNIH5/Taheri et al. - 2023 - Understanding and leveraging short-range order in .pdf:application/pdf},\n}\n\n\n\n In this article, we review the opportunities and challenges associated with complex concentrated materials that exhibit short-range order. Although the presence of such phenomena has been theorized, accurate computational representation, characterization, and materials design have clear challenges associated with its complexity. Advances in both high-resolution and high-fidelity methods, as well as machine-learning-aided techniques, have paved a path for realization of complex concentrated systems with deterministic short-range order, and provide a foundation on which these alloys and materials can be developed for various applications in functional, structural, and biomedical applications.\n
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\n\n \n \n 2021\n \n \n (1)\n \n \n
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\n \n \n\n \n \n \n \n \n \n The pursuit of stability in halide perovskites: the monovalent cation and the key for surface and bulk self-healing.\n \n \n \n \n\n\n \n R. Ceratti, D.; V. Cohen, A.; Tenne, R.; Rakita, Y.; Snarski, L.; P. Jasti, N.; Cremonesi, L.; Cohen, R.; Weitman, M.; Rosenhek-Goldian, I.; Kaplan-Ashiri, I.; Bendikov, T.; Kalchenko, V.; Elbaum, M.; C. Potenza, M. A.; Kronik, L.; Hodes, G.; and Cahen, D.\n\n\n \n\n\n\n Materials Horizons, 8(5): 1570–1586. 2021.\n Publisher: Royal Society of Chemistry\n\n\n\n
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\n\n\n\n@article{rceratti_pursuit_2021,\n\ttitle = {The pursuit of stability in halide perovskites: the monovalent cation and the key for surface and bulk self-healing},\n\tvolume = {8},\n\tshorttitle = {The pursuit of stability in halide perovskites},\n\turl = {https://pubs.rsc.org/en/content/articlelanding/2021/mh/d1mh00006c},\n\tdoi = {10.1039/D1MH00006C},\n\tlanguage = {en},\n\tnumber = {5},\n\turldate = {2023-12-13},\n\tjournal = {Materials Horizons},\n\tauthor = {R. Ceratti, D. and V. Cohen, A. and Tenne, R. and Rakita, Y. and Snarski, L. and P. Jasti, N. and Cremonesi, L. and Cohen, R. and Weitman, M. and Rosenhek-Goldian, I. and Kaplan-Ashiri, I. and Bendikov, T. and Kalchenko, V. and Elbaum, M. and C. Potenza, M. A. and Kronik, L. and Hodes, G. and Cahen, D.},\n\tyear = {2021},\n\tnote = {Publisher: Royal Society of Chemistry},\n\tpages = {1570--1586},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/IQJ66F7U/R. Ceratti et al. - 2021 - The pursuit of stability in halide perovskites th.pdf:application/pdf},\n}\n\n\n\n
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\n \n \n\n \n \n \n \n \n \n Effect of Low Pressure on Tetragonal to Cubic Phase Transition of Methylammonium Lead Iodide Perovskite.\n \n \n \n \n\n\n \n Halder, A.; Rakita, Y.; Cahen, D.; and Sarkar, S. K.\n\n\n \n\n\n\n The Journal of Physical Chemistry Letters, 11(4): 1473–1476. February 2020.\n Publisher: American Chemical Society\n\n\n\n
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\n\n\n@article{halder_effect_2020,\n\ttitle = {Effect of {Low} {Pressure} on {Tetragonal} to {Cubic} {Phase} {Transition} of {Methylammonium} {Lead} {Iodide} {Perovskite}},\n\tvolume = {11},\n\turl = {https://doi.org/10.1021/acs.jpclett.9b03895},\n\tdoi = {10.1021/acs.jpclett.9b03895},\n\tabstract = {The attractive optoelectronic properties of MAPbI3 (MA = CH3NH3), one of the most common halide perovskites, can be complicated by its tetragonal → cubic structural phase transition just above room temperature. We show that decreasing the ambient pressure can move that phase transition by ∼40 °C (at ∼10–3 mbar). Our report also includes control experiments, which show that desorption of water or oxygen can be excluded as possible causes for the change in phase transition temperature. On the basis of diffraction data, we postulate that an optimum volume is required to initiate a T → C phase transition. The pressure-induced phase change in effect stabilizes the tetragonal phase for work around room temperature, even if some natural heating occurs.},\n\tnumber = {4},\n\turldate = {2023-12-13},\n\tjournal = {The Journal of Physical Chemistry Letters},\n\tauthor = {Halder, Ansuman and Rakita, Yevgeny and Cahen, David and Sarkar, Shaibal K.},\n\tmonth = feb,\n\tyear = {2020},\n\tnote = {Publisher: American Chemical Society},\n\tpages = {1473--1476},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/3XB3UMWQ/Halder et al. - 2020 - Effect of Low Pressure on Tetragonal to Cubic Phas.pdf:application/pdf},\n}\n\n\n\n The attractive optoelectronic properties of MAPbI3 (MA = CH3NH3), one of the most common halide perovskites, can be complicated by its tetragonal → cubic structural phase transition just above room temperature. We show that decreasing the ambient pressure can move that phase transition by ∼40 °C (at ∼10–3 mbar). Our report also includes control experiments, which show that desorption of water or oxygen can be excluded as possible causes for the change in phase transition temperature. On the basis of diffraction data, we postulate that an optimum volume is required to initiate a T → C phase transition. The pressure-induced phase change in effect stabilizes the tetragonal phase for work around room temperature, even if some natural heating occurs.\n
\n\n\n\n \n\n \n \n \n \n \n \n Origin of the anomalous Pb-Br bond dynamics in formamidinium lead bromide perovskites.\n \n \n \n \n\n\n \n Singh, H.; Fei, R.; Rakita, Y.; Kulbak, M.; Cahen, D.; Rappe, A. M.; and Frenkel, A. I.\n\n\n \n\n\n\n Physical Review B, 101(5): 054302. February 2020.\n Publisher: American Physical Society\n\n\n\n
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\n\n\n@article{singh_origin_2020,\n\ttitle = {Origin of the anomalous {Pb}-{Br} bond dynamics in formamidinium lead bromide perovskites},\n\tvolume = {101},\n\turl = {https://link.aps.org/doi/10.1103/PhysRevB.101.054302},\n\tdoi = {10.1103/PhysRevB.101.054302},\n\tabstract = {Extended x-ray absorption fine structure spectroscopy of the light-harvesting formamidinium lead bromide (FAPbBr3) perovskite, a system with attractive optoelectronic performance, shows anomalously large variance in Pb-Br bond length, some 50\\% larger than in its inorganic CsPbBr3 counterpart. Using first-principles molecular dynamics simulations, we find a significant contribution to this variance coming from the FA cation, and show that the FA does not just tumble in its cuboctahedral Br12 cage, but instead stochastically sticks to, and detaches from one of the 12 nearest Br atoms after another, leading to the large variance in Pb-Br bond length. Our results demonstrate dynamic coupling between the FA-Br moiety and perovskite cage vibrations, and that tunability in dynamics can be achieved by changing the cation type and perovskite lattice parameter. Thus, our results provide information that needs to be considered in any of the intensely debated models of electron-phonon coupling in lead halide perovskites.},\n\tnumber = {5},\n\turldate = {2023-12-13},\n\tjournal = {Physical Review B},\n\tauthor = {Singh, Harishchandra and Fei, Ruixiang and Rakita, Yevgeny and Kulbak, Michael and Cahen, David and Rappe, Andrew M. and Frenkel, Anatoly I.},\n\tmonth = feb,\n\tyear = {2020},\n\tnote = {Publisher: American Physical Society},\n\tpages = {054302},\n\tfile = {APS Snapshot:/Users/yevgenyr/Zotero/storage/4LCCZ969/PhysRevB.101.html:text/html;Full Text PDF:/Users/yevgenyr/Zotero/storage/I934NCNB/Singh et al. - 2020 - Origin of the anomalous Pb-Br bond dynamics in for.pdf:application/pdf},\n}\n\n\n\n Extended x-ray absorption fine structure spectroscopy of the light-harvesting formamidinium lead bromide (FAPbBr3) perovskite, a system with attractive optoelectronic performance, shows anomalously large variance in Pb-Br bond length, some 50% larger than in its inorganic CsPbBr3 counterpart. Using first-principles molecular dynamics simulations, we find a significant contribution to this variance coming from the FA cation, and show that the FA does not just tumble in its cuboctahedral Br12 cage, but instead stochastically sticks to, and detaches from one of the 12 nearest Br atoms after another, leading to the large variance in Pb-Br bond length. Our results demonstrate dynamic coupling between the FA-Br moiety and perovskite cage vibrations, and that tunability in dynamics can be achieved by changing the cation type and perovskite lattice parameter. Thus, our results provide information that needs to be considered in any of the intensely debated models of electron-phonon coupling in lead halide perovskites.\n
\n\n\n\n \n\n \n \n \n \n \n \n Lattice mode symmetry analysis of the orthorhombic phase of methylammonium lead iodide using polarized Raman.\n \n \n \n \n\n\n \n Sharma, R.; Menahem, M.; Dai, Z.; Gao, L.; Brenner, T. M.; Yadgarov, L.; Zhang, J.; Rakita, Y.; Korobko, R.; Pinkas, I.; Rappe, A. M.; and Yaffe, O.\n\n\n \n\n\n\n Physical Review Materials, 4(5): 051601. May 2020.\n Publisher: American Physical Society\n\n\n\n
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\n\n\n@article{sharma_lattice_2020,\n\ttitle = {Lattice mode symmetry analysis of the orthorhombic phase of methylammonium lead iodide using polarized {Raman}},\n\tvolume = {4},\n\turl = {https://link.aps.org/doi/10.1103/PhysRevMaterials.4.051601},\n\tdoi = {10.1103/PhysRevMaterials.4.051601},\n\tabstract = {In the last decade, hybrid organic-inorganic halide perovskites have emerged as a new type of semiconductor for photovoltaics and other optoelectronic applications. Unlike standard, tetrahedrally bonded semiconductors (e.g., Si and GaAs), the ionic thermal fluctuations in the halide perovskites (i.e., structural dynamics) are strongly coupled to the electronic dynamics. Therefore, it is crucial to obtain accurate and detailed knowledge about the nature of the atomic motions within the crystal. This has proved to be challenging due to low thermal stability and the complex, temperature-dependent structural phase sequence of the halide perovskites. Here, these challenges are overcome and a detailed analysis of the low-frequency lattice mode symmetries is provided in the low-temperature orthorhombic phase of methylammonium-lead iodide. Raman measurements using linearly and circularly polarized light at 1.16 eV excitation are combined with density functional perturbation theory (DFPT). By performing an iterative analysis of Raman polarization-orientation dependence and DFPT mode analysis, the crystal orientation is determined. Subsequently, accounting for birefringence effects detected using circularly polarized light excitation, the symmetries of all of the observed Raman-active modes at 10 K are assigned.},\n\tnumber = {5},\n\turldate = {2023-12-13},\n\tjournal = {Physical Review Materials},\n\tauthor = {Sharma, Rituraj and Menahem, Matan and Dai, Zhenbang and Gao, Lingyuan and Brenner, Thomas M. and Yadgarov, Lena and Zhang, Jiahao and Rakita, Yevgeny and Korobko, Roman and Pinkas, Iddo and Rappe, Andrew M. and Yaffe, Omer},\n\tmonth = may,\n\tyear = {2020},\n\tnote = {Publisher: American Physical Society},\n\tpages = {051601},\n\tfile = {APS Snapshot:/Users/yevgenyr/Zotero/storage/86DWALT4/PhysRevMaterials.4.html:text/html;Full Text PDF:/Users/yevgenyr/Zotero/storage/BXRTIRPU/Sharma et al. - 2020 - Lattice mode symmetry analysis of the orthorhombic.pdf:application/pdf},\n}\n\n\n\n In the last decade, hybrid organic-inorganic halide perovskites have emerged as a new type of semiconductor for photovoltaics and other optoelectronic applications. Unlike standard, tetrahedrally bonded semiconductors (e.g., Si and GaAs), the ionic thermal fluctuations in the halide perovskites (i.e., structural dynamics) are strongly coupled to the electronic dynamics. Therefore, it is crucial to obtain accurate and detailed knowledge about the nature of the atomic motions within the crystal. This has proved to be challenging due to low thermal stability and the complex, temperature-dependent structural phase sequence of the halide perovskites. Here, these challenges are overcome and a detailed analysis of the low-frequency lattice mode symmetries is provided in the low-temperature orthorhombic phase of methylammonium-lead iodide. Raman measurements using linearly and circularly polarized light at 1.16 eV excitation are combined with density functional perturbation theory (DFPT). By performing an iterative analysis of Raman polarization-orientation dependence and DFPT mode analysis, the crystal orientation is determined. Subsequently, accounting for birefringence effects detected using circularly polarized light excitation, the symmetries of all of the observed Raman-active modes at 10 K are assigned.\n
\n\n\n\n \n\n \n \n \n \n \n \n Single-Crystal Growth and Thermal Stability of (CH3NH3)1–xCsxPbBr3.\n \n \n \n \n\n\n \n Kaslasi, H.; Feldman, Y.; Rakita, Y.; Cahen, D.; and Hodes, G.\n\n\n \n\n\n\n Crystal Growth & Design, 20(7): 4366–4374. July 2020.\n Publisher: American Chemical Society\n\n\n\n
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\n\n\n@article{kaslasi_single-crystal_2020,\n\ttitle = {Single-{Crystal} {Growth} and {Thermal} {Stability} of ({CH3NH3})1–{xCsxPbBr3}},\n\tvolume = {20},\n\tissn = {1528-7483},\n\turl = {https://doi.org/10.1021/acs.cgd.0c00122},\n\tdoi = {10.1021/acs.cgd.0c00122},\n\tabstract = {We describe the growth of single crystals of the halide perovskites APbBr3, with varying ratios of Cs to methylammonium (MA) on the A site, by antisolvent vapor-assisted crystallization (AVC) and characterize the structural and compositional homogeneity of the grown crystals. We find improved thermostability for the Cs-rich mixed crystals and suggest that this is caused by a combination of locking-in of the relatively large MA in the smaller lattice of the Cs-rich material as well as by stronger hydrogen bonding between the nitrogen of MA and Br due to reduced lattice size and/or octahedral tilting with increased Cs. We also show that it is possible to grow either compositionally homogeneous crystals or core–shell, compositionally graded crystals by changing the ratio of antisolvent to solvent in the AVC method.},\n\tnumber = {7},\n\turldate = {2023-12-13},\n\tjournal = {Crystal Growth \\& Design},\n\tauthor = {Kaslasi, Hadar and Feldman, Yishay and Rakita, Yevgeny and Cahen, David and Hodes, Gary},\n\tmonth = jul,\n\tyear = {2020},\n\tnote = {Publisher: American Chemical Society},\n\tpages = {4366--4374},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/Y868DSY5/Kaslasi et al. - 2020 - Single-Crystal Growth and Thermal Stability of (CH.pdf:application/pdf},\n}\n\n\n\n We describe the growth of single crystals of the halide perovskites APbBr3, with varying ratios of Cs to methylammonium (MA) on the A site, by antisolvent vapor-assisted crystallization (AVC) and characterize the structural and compositional homogeneity of the grown crystals. We find improved thermostability for the Cs-rich mixed crystals and suggest that this is caused by a combination of locking-in of the relatively large MA in the smaller lattice of the Cs-rich material as well as by stronger hydrogen bonding between the nitrogen of MA and Br due to reduced lattice size and/or octahedral tilting with increased Cs. We also show that it is possible to grow either compositionally homogeneous crystals or core–shell, compositionally graded crystals by changing the ratio of antisolvent to solvent in the AVC method.\n
\n\n\n\n \n\n \n \n \n \n \n \n Elucidating the atomistic origin of anharmonicity in tetragonal CH3NH3PbI3 with Raman scattering.\n \n \n \n \n\n\n \n Sharma, R.; Dai, Z.; Gao, L.; Brenner, T. M.; Yadgarov, L.; Zhang, J.; Rakita, Y.; Korobko, R.; Rappe, A. M.; and Yaffe, O.\n\n\n \n\n\n\n Physical Review Materials, 4(9): 092401. September 2020.\n Publisher: American Physical Society\n\n\n\n
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\n\n\n@article{sharma_elucidating_2020,\n\ttitle = {Elucidating the atomistic origin of anharmonicity in tetragonal {CH3NH3PbI3} with {Raman} scattering},\n\tvolume = {4},\n\turl = {https://link.aps.org/doi/10.1103/PhysRevMaterials.4.092401},\n\tdoi = {10.1103/PhysRevMaterials.4.092401},\n\tabstract = {Halide perovskite (HP) semiconductors exhibit unique strong coupling between the electronic and structural dynamics. We use Raman polarization-orientation (PO) measurements and ab initio molecular dynamics (AIMD) to investigate the origin and temperature evolution of the strong structural anharmonicity throughout the tetragonal phase of CH3NH3PbI3. Raman PO measurements reveal a soft modelike spectral feature. This mode shows an unusual continuous increase in damping with temperature which is indicative of an anharmonic potential surface. The analysis of AIMD trajectories identifies two major sources of anharmonicity: the orientational unlocking of the [CH3NH3]+ ions and large-amplitude octahedral tilting that continuously increases with temperature. Our work suggests that the standard phonon picture cannot describe the structural dynamics of tetragonal CH3NH3PbI3.},\n\tnumber = {9},\n\turldate = {2023-12-13},\n\tjournal = {Physical Review Materials},\n\tauthor = {Sharma, Rituraj and Dai, Zhenbang and Gao, Lingyuan and Brenner, Thomas M. and Yadgarov, Lena and Zhang, Jiahao and Rakita, Yevgeny and Korobko, Roman and Rappe, Andrew M. and Yaffe, Omer},\n\tmonth = sep,\n\tyear = {2020},\n\tnote = {Publisher: American Physical Society},\n\tpages = {092401},\n\tfile = {APS Snapshot:/Users/yevgenyr/Zotero/storage/QKGYDY3V/PhysRevMaterials.4.html:text/html;Full Text PDF:/Users/yevgenyr/Zotero/storage/SR68EQ9H/Sharma et al. - 2020 - Elucidating the atomistic origin of anharmonicity .pdf:application/pdf},\n}\n\n\n\n Halide perovskite (HP) semiconductors exhibit unique strong coupling between the electronic and structural dynamics. We use Raman polarization-orientation (PO) measurements and ab initio molecular dynamics (AIMD) to investigate the origin and temperature evolution of the strong structural anharmonicity throughout the tetragonal phase of CH3NH3PbI3. Raman PO measurements reveal a soft modelike spectral feature. This mode shows an unusual continuous increase in damping with temperature which is indicative of an anharmonic potential surface. The analysis of AIMD trajectories identifies two major sources of anharmonicity: the orientational unlocking of the [CH3NH3]+ ions and large-amplitude octahedral tilting that continuously increases with temperature. Our work suggests that the standard phonon picture cannot describe the structural dynamics of tetragonal CH3NH3PbI3.\n
\n\n\n\n \n\n \n \n \n \n \n \n Active Reaction Control of Cu Redox State Based on Real-Time Feedback from In Situ Synchrotron Measurements.\n \n \n \n \n\n\n \n Rakita, Y.; O’Nolan, D.; McAuliffe, R. D.; Veith, G. M.; Chupas, P. J.; Billinge, S. J. L.; and Chapman, K. W.\n\n\n \n\n\n\n Journal of the American Chemical Society, 142(44): 18758–18762. November 2020.\n Publisher: American Chemical Society\n\n\n\n
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\n\n\n@article{rakita_active_2020,\n\ttitle = {Active {Reaction} {Control} of {Cu} {Redox} {State} {Based} on {Real}-{Time} {Feedback} from {In} {Situ} {Synchrotron} {Measurements}},\n\tvolume = {142},\n\tissn = {0002-7863},\n\turl = {https://doi.org/10.1021/jacs.0c09418},\n\tdoi = {10.1021/jacs.0c09418},\n\tabstract = {We achieve a target material state by using a recursive algorithm to control the material reaction based on real-time feedback on the system chemistry from in situ X-ray absorption spectroscopy. Without human intervention, the algorithm controlled O2:H2 gas partial pressures to approach a target average Cu oxidation state of 1+ for γ-Al2O3-supported Cu. This approach represents a new paradigm in autonomation for materials discovery and synthesis optimization; instead of iterating the parameters following the conclusion of each of a series of reactions, the iteration cycle has been scaled down to time points during an individual reaction. Application of the proof-of-concept illustrated here, using a feedback loop to couple in situ material characterization and the reaction conditions via a decision-making algorithm, can be readily envisaged in optimizing and understanding a broad range of systems including catalysis.},\n\tnumber = {44},\n\turldate = {2023-12-13},\n\tjournal = {Journal of the American Chemical Society},\n\tauthor = {Rakita, Yevgeny and O’Nolan, Daniel and McAuliffe, Rebecca D. and Veith, Gabriel M. and Chupas, Peter J. and Billinge, Simon J. L. and Chapman, Karena W.},\n\tmonth = nov,\n\tyear = {2020},\n\tnote = {Publisher: American Chemical Society},\n\tpages = {18758--18762},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/ZYWPMZE9/Rakita et al. - 2020 - Active Reaction Control of Cu Redox State Based on.pdf:application/pdf},\n}\n\n\n\n We achieve a target material state by using a recursive algorithm to control the material reaction based on real-time feedback on the system chemistry from in situ X-ray absorption spectroscopy. Without human intervention, the algorithm controlled O2:H2 gas partial pressures to approach a target average Cu oxidation state of 1+ for γ-Al2O3-supported Cu. This approach represents a new paradigm in autonomation for materials discovery and synthesis optimization; instead of iterating the parameters following the conclusion of each of a series of reactions, the iteration cycle has been scaled down to time points during an individual reaction. Application of the proof-of-concept illustrated here, using a feedback loop to couple in situ material characterization and the reaction conditions via a decision-making algorithm, can be readily envisaged in optimizing and understanding a broad range of systems including catalysis.\n
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\n \n \n\n \n \n \n \n \n \n When defects become ‘dynamic’: halide perovskites: a new window on materials?.\n \n \n \n \n\n\n \n Rakita, Y.; Lubomirsky, I.; and Cahen, D.\n\n\n \n\n\n\n Materials Horizons, 6(7): 1297–1305. 2019.\n Publisher: Royal Society of Chemistry\n\n\n\n
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\n\n\n\n@article{rakita_when_2019,\n\ttitle = {When defects become ‘dynamic’: halide perovskites: a new window on materials?},\n\tvolume = {6},\n\tshorttitle = {When defects become ‘dynamic’},\n\turl = {https://pubs.rsc.org/en/content/articlelanding/2019/mh/c9mh00606k},\n\tdoi = {10.1039/C9MH00606K},\n\tlanguage = {en},\n\tnumber = {7},\n\turldate = {2023-12-13},\n\tjournal = {Materials Horizons},\n\tauthor = {Rakita, Yevgeny and Lubomirsky, Igor and Cahen, David},\n\tyear = {2019},\n\tnote = {Publisher: Royal Society of Chemistry},\n\tpages = {1297--1305},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/WFFIPXYV/Rakita et al. - 2019 - When defects become ‘dynamic’ halide perovskites.pdf:application/pdf},\n}\n\n\n\n \n\n \n \n \n \n \n \n Process for the preparation of halide perovskite and perovskite-related materials.\n \n \n \n \n\n\n \n Cahen, D.; MODES, G.; RAKITA, Y.; and KEDEM, N.\n\n\n \n\n\n\n June 2019.\n \n\n\n\n
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\n\n\n\n@patent{cahen_process_2019,\n\ttitle = {Process for the preparation of halide perovskite and perovskite-related materials},\n\turl = {https://patents.google.com/patent/US20190185495A1/en},\n\tnationality = {US},\n\tassignee = {Ye Da Research And Development Co Ltd},\n\tnumber = {US20190185495A1},\n\turldate = {2023-12-13},\n\tauthor = {Cahen, David and MODES, Gary and RAKITA, Yevgeny and KEDEM, Nir},\n\tmonth = jun,\n\tyear = {2019},\n\tkeywords = {perovskite, cation, combination, halide, metal},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/B9KPZ6KQ/Cahen et al. - 2019 - Process for the preparation of halide perovskite a.pdf:application/pdf},\n}\n\n\n\n \n\n \n \n \n \n \n \n Type and Degree of Covalence: Empirical Derivation and Implications.\n \n \n \n \n\n\n \n Rakita, Y.; Kirchartz, T.; Hodes, G.; and Cahen, D.\n\n\n \n\n\n\n July 2019.\n arXiv:1907.03971 [cond-mat]\n\n\n\n
\n\n\n\n \n \nPaper\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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\n\n\n@misc{rakita_type_2019,\n\ttitle = {Type and {Degree} of {Covalence}: {Empirical} {Derivation} and {Implications}},\n\tshorttitle = {Type and {Degree} of {Covalence}},\n\turl = {http://arxiv.org/abs/1907.03971},\n\tdoi = {10.48550/arXiv.1907.03971},\n\tabstract = {The way atoms attach to each other defines the function(s), e.g., mechanical, optical, electronic, of a given material. The nature of the chemical bond is, therefore, one of the most fundamental issues in materials. Both ionic interactions, i.e., resulting from electrical charges associated with the atoms, and covalent ones, i.e., the sharing of electrons between nuclei of different atoms, are usually viewed as forces that attract between atoms to form a rigid structure. Although less common for solid materials, it was shown theoretically to be possible for covalent interactions at the chemically-active electronic shell (or valence-band maximum) of semiconductors to reverse their more common nature and become repulsive, i.e., act against bonding. Some semiconductors with such predicted anti-bonding valence-band maximum levels (such as halide perovskites) show experimentally some amazing (opto-) electronic properties. Predictions that anti-bonding character can allow tolerance for existing defects, at least in part, can explain the superior properties of such semiconductors. Although there are known experimental ways to estimate the degree of the covalent nature (e.g., electronegativity), this was not possible hitherto for the type, i.e., distinguishing whether a material exhibits bonding or anti-bonding covalent interactions. We have developed a simple way to reveal the complete nature (both type and degree) of chemical bonds, using experimental data. After confirming our development with classical models and theoretical predictions, with a set of {\\textasciitilde}40 different functional semi-conductors, we show how knowledge of the complete nature of covalent bonding is of critical importance for fundamental properties of semiconductors.},\n\turldate = {2023-12-13},\n\tpublisher = {arXiv},\n\tauthor = {Rakita, Yevgeny and Kirchartz, Thomas and Hodes, Gary and Cahen, David},\n\tmonth = jul,\n\tyear = {2019},\n\tnote = {arXiv:1907.03971 [cond-mat]},\n\tkeywords = {Condensed Matter - Materials Science},\n\tfile = {arXiv Fulltext PDF:/Users/yevgenyr/Zotero/storage/SMW7FJP2/Rakita et al. - 2019 - Type and Degree of Covalence Empirical Derivation.pdf:application/pdf;arXiv.org Snapshot:/Users/yevgenyr/Zotero/storage/VA9Y24IZ/1907.html:text/html},\n}\n\n\n\n The way atoms attach to each other defines the function(s), e.g., mechanical, optical, electronic, of a given material. The nature of the chemical bond is, therefore, one of the most fundamental issues in materials. Both ionic interactions, i.e., resulting from electrical charges associated with the atoms, and covalent ones, i.e., the sharing of electrons between nuclei of different atoms, are usually viewed as forces that attract between atoms to form a rigid structure. Although less common for solid materials, it was shown theoretically to be possible for covalent interactions at the chemically-active electronic shell (or valence-band maximum) of semiconductors to reverse their more common nature and become repulsive, i.e., act against bonding. Some semiconductors with such predicted anti-bonding valence-band maximum levels (such as halide perovskites) show experimentally some amazing (opto-) electronic properties. Predictions that anti-bonding character can allow tolerance for existing defects, at least in part, can explain the superior properties of such semiconductors. Although there are known experimental ways to estimate the degree of the covalent nature (e.g., electronegativity), this was not possible hitherto for the type, i.e., distinguishing whether a material exhibits bonding or anti-bonding covalent interactions. We have developed a simple way to reveal the complete nature (both type and degree) of chemical bonds, using experimental data. After confirming our development with classical models and theoretical predictions, with a set of ~40 different functional semi-conductors, we show how knowledge of the complete nature of covalent bonding is of critical importance for fundamental properties of semiconductors.\n
\n\n\n\n \n\n \n \n \n \n \n \n Ultrafast Charge Carrier Relaxation in Inorganic Halide Perovskite Single Crystals Probed by Two-Dimensional Electronic Spectroscopy.\n \n \n \n \n\n\n \n Nguyen, X. T.; Timmer, D.; Rakita, Y.; Cahen, D.; Steinhoff, A.; Jahnke, F.; Lienau, C.; and De Sio, A.\n\n\n \n\n\n\n The Journal of Physical Chemistry Letters, 10(18): 5414–5421. September 2019.\n Publisher: American Chemical Society\n\n\n\n
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\n\n\n@article{nguyen_ultrafast_2019,\n\ttitle = {Ultrafast {Charge} {Carrier} {Relaxation} in {Inorganic} {Halide} {Perovskite} {Single} {Crystals} {Probed} by {Two}-{Dimensional} {Electronic} {Spectroscopy}},\n\tvolume = {10},\n\turl = {https://doi.org/10.1021/acs.jpclett.9b01936},\n\tdoi = {10.1021/acs.jpclett.9b01936},\n\tabstract = {Halide perovskites are promising optoelectronic materials. Despite impressive device performance, especially in photovoltaics, the femtosecond dynamics of elementary optical excitations and their interactions are still debated. Here we combine ultrafast two-dimensional electronic spectroscopy (2DES) and semiconductor Bloch equations (SBEs) to probe the room-temperature dynamics of nonequilibrium excitations in CsPbBr3 crystals. Experimentally, we distinguish between excitonic and free-carrier transitions, extracting a ∼30 meV exciton binding energy, in agreement with our SBE calculations and with recent experimental studies. The 2DES dynamics indicate remarkably short, {\\textless}30 fs carrier relaxation at a ∼3 meV/fs rate, much faster than previously anticipated for this material, but similar to that in direct band gap semiconductors such as GaAs. Dynamic screening of excitons by free carriers also develops on a similarly fast {\\textless}30 fs time scale, emphasizing the role of carrier–carrier interactions for this material’s optical properties. Our results suggest that strong electron–phonon couplings lead to ultrafast relaxation of charge carriers, which, in turn may limit halide perovskites’ carrier mobilities.},\n\tnumber = {18},\n\turldate = {2023-12-13},\n\tjournal = {The Journal of Physical Chemistry Letters},\n\tauthor = {Nguyen, Xuan Trung and Timmer, Daniel and Rakita, Yevgeny and Cahen, David and Steinhoff, Alexander and Jahnke, Frank and Lienau, Christoph and De Sio, Antonietta},\n\tmonth = sep,\n\tyear = {2019},\n\tnote = {Publisher: American Chemical Society},\n\tpages = {5414--5421},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/CUZ6XLDB/Nguyen et al. - 2019 - Ultrafast Charge Carrier Relaxation in Inorganic H.pdf:application/pdf},\n}\n\n\n\n Halide perovskites are promising optoelectronic materials. Despite impressive device performance, especially in photovoltaics, the femtosecond dynamics of elementary optical excitations and their interactions are still debated. Here we combine ultrafast two-dimensional electronic spectroscopy (2DES) and semiconductor Bloch equations (SBEs) to probe the room-temperature dynamics of nonequilibrium excitations in CsPbBr3 crystals. Experimentally, we distinguish between excitonic and free-carrier transitions, extracting a ∼30 meV exciton binding energy, in agreement with our SBE calculations and with recent experimental studies. The 2DES dynamics indicate remarkably short, \\textless30 fs carrier relaxation at a ∼3 meV/fs rate, much faster than previously anticipated for this material, but similar to that in direct band gap semiconductors such as GaAs. Dynamic screening of excitons by free carriers also develops on a similarly fast \\textless30 fs time scale, emphasizing the role of carrier–carrier interactions for this material’s optical properties. Our results suggest that strong electron–phonon couplings lead to ultrafast relaxation of charge carriers, which, in turn may limit halide perovskites’ carrier mobilities.\n
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\n \n \n\n \n \n \n \n \n \n Self-Healing Inside APbBr3 Halide Perovskite Crystals.\n \n \n \n \n\n\n \n Ceratti, D. R.; Rakita, Y.; Cremonesi, L.; Tenne, R.; Kalchenko, V.; Elbaum, M.; Oron, D.; Potenza, M. A. C.; Hodes, G.; and Cahen, D.\n\n\n \n\n\n\n Advanced Materials, 30(10): 1706273. 2018.\n _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201706273\n\n\n\n
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\n\n\n@article{ceratti_self-healing_2018,\n\ttitle = {Self-{Healing} {Inside} {APbBr3} {Halide} {Perovskite} {Crystals}},\n\tvolume = {30},\n\tcopyright = {© 2018 WILEY-VCH Verlag GmbH \\& Co. KGaA, Weinheim},\n\tissn = {1521-4095},\n\turl = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201706273},\n\tdoi = {10.1002/adma.201706273},\n\tabstract = {Self-healing, where a modification in some parameter is reversed with time without any external intervention, is one of the particularly interesting properties of halide perovskites. While there are a number of studies showing such self-healing in perovskites, they all are carried out on thin films, where the interface between the perovskite and another phase (including the ambient) is often a dominating and interfering factor in the process. Here, self-healing in perovskite (methylammonium, formamidinium, and cesium lead bromide (MAPbBr3, FAPbBr3, and CsPbBr3)) single crystals is reported, using two-photon microscopy to create damage (photobleaching) ≈110 µm inside the crystals and to monitor the recovery of photoluminescence after the damage. Self-healing occurs in all three perovskites with FAPbBr3 the fastest (≈1 h) and CsPbBr3 the slowest (tens of hours) to recover. This behavior, different from surface-dominated stability trends, is typical of the bulk and is strongly dependent on the localization of degradation products not far from the site of the damage. The mechanism of self-healing is discussed with the possible participation of polybromide species. It provides a closed chemical cycle and does not necessarily involve defect or ion migration phenomena that are often proposed to explain reversible phenomena in halide perovskites.},\n\tlanguage = {en},\n\tnumber = {10},\n\turldate = {2023-12-13},\n\tjournal = {Advanced Materials},\n\tauthor = {Ceratti, Davide Raffaele and Rakita, Yevgeny and Cremonesi, Llorenç and Tenne, Ron and Kalchenko, Vyacheslav and Elbaum, Michael and Oron, Dan and Potenza, Marco Alberto Carlo and Hodes, Gary and Cahen, David},\n\tyear = {2018},\n\tnote = {\\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201706273},\n\tkeywords = {bleaching, halide perovskites, photoluminescence, self-healing, self-repair},\n\tpages = {1706273},\n\tfile = {Snapshot:/Users/yevgenyr/Zotero/storage/59CMJVUZ/adma.html:text/html},\n}\n\n\n\n Self-healing, where a modification in some parameter is reversed with time without any external intervention, is one of the particularly interesting properties of halide perovskites. While there are a number of studies showing such self-healing in perovskites, they all are carried out on thin films, where the interface between the perovskite and another phase (including the ambient) is often a dominating and interfering factor in the process. Here, self-healing in perovskite (methylammonium, formamidinium, and cesium lead bromide (MAPbBr3, FAPbBr3, and CsPbBr3)) single crystals is reported, using two-photon microscopy to create damage (photobleaching) ≈110 µm inside the crystals and to monitor the recovery of photoluminescence after the damage. Self-healing occurs in all three perovskites with FAPbBr3 the fastest (≈1 h) and CsPbBr3 the slowest (tens of hours) to recover. This behavior, different from surface-dominated stability trends, is typical of the bulk and is strongly dependent on the localization of degradation products not far from the site of the damage. The mechanism of self-healing is discussed with the possible participation of polybromide species. It provides a closed chemical cycle and does not necessarily involve defect or ion migration phenomena that are often proposed to explain reversible phenomena in halide perovskites.\n
\n\n\n\n \n\n \n \n \n \n \n \n Between Structure and Performance in Halide Perovskites for Photovoltaic Applications: the Role of Defects.\n \n \n \n \n\n\n \n Rakita, Y.\n\n\n \n\n\n\n Ph.D. Thesis, The Weizmann Institute of Science (Israel), Israel, 2018.\n ISBN: 9798438790037\n\n\n\n
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\n\n\n@phdthesis{rakita_between_2018,\n\taddress = {Israel},\n\ttype = {Ph.{D}.},\n\ttitle = {Between {Structure} and {Performance} in {Halide} {Perovskites} for {Photovoltaic} {Applications}: the {Role} of {Defects}},\n\tcopyright = {Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.},\n\tshorttitle = {Between {Structure} and {Performance} in {Halide} {Perovskites} for {Photovoltaic} {Applications}},\n\turl = {https://www.proquest.com/docview/2669102985/abstract/C0116400F0D7467BPQ/1},\n\tabstract = {Halide Perovskite (HaP) semiconducting compounds with an ABX3 stoichiometry and a (pseudo-) cubic symmetry, where the X group is a halide (I- , Bror Cl- ), B is a metal of the IV column (e.g., Pb or Sn) and A is a cation (organic or inorganic). My main motivation to study HaPs is their proven high outputs in converting sunlight to electricity in photovoltaic (PV) cells ({\\textgreater}22\\%)9 , although, with respect to other solar-cell technologies, much simpler (solution-based) fabrication methods are required. My study focused on the fundamental structural, chemical and dielectric properties of HaPs in reference to their PV-related properties. Since the main focus of the study relates to intrinsic properties of HaPs, single-crystals were the main model-of-choice for my experiments. Their growth and characterizations can be found in chapter 2. I do note that while film morphology, grain boundaries and different interfacing materials may be very important for device operation, these were not considered in my work.},\n\tlanguage = {English},\n\turldate = {2023-12-13},\n\tschool = {The Weizmann Institute of Science (Israel)},\n\tauthor = {Rakita, Yevgeny},\n\tyear = {2018},\n\tdoi = {10.34933/wis.000422},\n\tnote = {ISBN: 9798438790037},\n\tkeywords = {Single crystals, Crystal structure, Semiconductors, Mechanical properties, Chemistry, Condensed matter physics, Metals, Deformation, Energy, Point defects, Atomic physics, Dielectric properties, Nuclear magnetic resonance--NMR, Radiation, Symmetry},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/WWJVDR2K/Rakita - 2018 - Between Structure and Performance in Halide Perovs.pdf:application/pdf},\n}\n\n\n\n Halide Perovskite (HaP) semiconducting compounds with an ABX3 stoichiometry and a (pseudo-) cubic symmetry, where the X group is a halide (I- , Bror Cl- ), B is a metal of the IV column (e.g., Pb or Sn) and A is a cation (organic or inorganic). My main motivation to study HaPs is their proven high outputs in converting sunlight to electricity in photovoltaic (PV) cells (\\textgreater22%)9 , although, with respect to other solar-cell technologies, much simpler (solution-based) fabrication methods are required. My study focused on the fundamental structural, chemical and dielectric properties of HaPs in reference to their PV-related properties. Since the main focus of the study relates to intrinsic properties of HaPs, single-crystals were the main model-of-choice for my experiments. Their growth and characterizations can be found in chapter 2. I do note that while film morphology, grain boundaries and different interfacing materials may be very important for device operation, these were not considered in my work.\n
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\n \n \n\n \n \n \n \n \n \n Tetragonal CH3NH3PbI3 is ferroelectric.\n \n \n \n \n\n\n \n Rakita, Y.; Bar-Elli, O.; Meirzadeh, E.; Kaslasi, H.; Peleg, Y.; Hodes, G.; Lubomirsky, I.; Oron, D.; Ehre, D.; and Cahen, D.\n\n\n \n\n\n\n Proceedings of the National Academy of Sciences, 114(28): E5504–E5512. July 2017.\n Publisher: Proceedings of the National Academy of Sciences\n\n\n\n
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\n\n\n@article{rakita_tetragonal_2017,\n\ttitle = {Tetragonal {CH3NH3PbI3} is ferroelectric},\n\tvolume = {114},\n\turl = {https://www.pnas.org/doi/abs/10.1073/pnas.1702429114},\n\tdoi = {10.1073/pnas.1702429114},\n\tabstract = {Halide perovskite (HaP) semiconductors are revolutionizing photovoltaic (PV) solar energy conversion by showing remarkable performance of solar cells made with HaPs, especially tetragonal methylammonium lead triiodide (MAPbI3). In particular, the low voltage loss of these cells implies a remarkably low recombination rate of photogenerated carriers. It was suggested that low recombination can be due to the spatial separation of electrons and holes, a possibility if MAPbI3 is a semiconducting ferroelectric, which, however, requires clear experimental evidence. As a first step, we show that, in operando, MAPbI3 (unlike MAPbBr3) is pyroelectric, which implies it can be ferroelectric. The next step, proving it is (not) ferroelectric, is challenging, because of the material’s relatively high electrical conductance (a consequence of an optical band gap suitable for PV conversion) and low stability under high applied bias voltage. This excludes normal measurements of a ferroelectric hysteresis loop, to prove ferroelectricity’s hallmark switchable polarization. By adopting an approach suitable for electrically leaky materials as MAPbI3, we show here ferroelectric hysteresis from well-characterized single crystals at low temperature (still within the tetragonal phase, which is stable at room temperature). By chemical etching, we also can image the structural fingerprint for ferroelectricity, polar domains, periodically stacked along the polar axis of the crystal, which, as predicted by theory, scale with the overall crystal size. We also succeeded in detecting clear second harmonic generation, direct evidence for the material’s noncentrosymmetry. We note that the material’s ferroelectric nature, can, but need not be important in a PV cell at room temperature.},\n\tnumber = {28},\n\turldate = {2023-12-13},\n\tjournal = {Proceedings of the National Academy of Sciences},\n\tauthor = {Rakita, Yevgeny and Bar-Elli, Omri and Meirzadeh, Elena and Kaslasi, Hadar and Peleg, Yagel and Hodes, Gary and Lubomirsky, Igor and Oron, Dan and Ehre, David and Cahen, David},\n\tmonth = jul,\n\tyear = {2017},\n\tnote = {Publisher: Proceedings of the National Academy of Sciences},\n\tpages = {E5504--E5512},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/IKVGU5R5/Rakita et al. - 2017 - Tetragonal CH3NH3PbI3 is ferroelectric.pdf:application/pdf},\n}\n\n\n\n Halide perovskite (HaP) semiconductors are revolutionizing photovoltaic (PV) solar energy conversion by showing remarkable performance of solar cells made with HaPs, especially tetragonal methylammonium lead triiodide (MAPbI3). In particular, the low voltage loss of these cells implies a remarkably low recombination rate of photogenerated carriers. It was suggested that low recombination can be due to the spatial separation of electrons and holes, a possibility if MAPbI3 is a semiconducting ferroelectric, which, however, requires clear experimental evidence. As a first step, we show that, in operando, MAPbI3 (unlike MAPbBr3) is pyroelectric, which implies it can be ferroelectric. The next step, proving it is (not) ferroelectric, is challenging, because of the material’s relatively high electrical conductance (a consequence of an optical band gap suitable for PV conversion) and low stability under high applied bias voltage. This excludes normal measurements of a ferroelectric hysteresis loop, to prove ferroelectricity’s hallmark switchable polarization. By adopting an approach suitable for electrically leaky materials as MAPbI3, we show here ferroelectric hysteresis from well-characterized single crystals at low temperature (still within the tetragonal phase, which is stable at room temperature). By chemical etching, we also can image the structural fingerprint for ferroelectricity, polar domains, periodically stacked along the polar axis of the crystal, which, as predicted by theory, scale with the overall crystal size. We also succeeded in detecting clear second harmonic generation, direct evidence for the material’s noncentrosymmetry. We note that the material’s ferroelectric nature, can, but need not be important in a PV cell at room temperature.\n
\n\n\n\n \n\n \n \n \n \n \n \n Laplace current deep level transient spectroscopy measurements of defect states in methylammonium lead bromide single crystals.\n \n \n \n \n\n\n \n Rosenberg, J. W.; Legodi, M. J.; Rakita, Y.; Cahen, D.; and Diale, M.\n\n\n \n\n\n\n Journal of Applied Physics, 122(14): 145701. October 2017.\n \n\n\n\n
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\n\n\n@article{rosenberg_laplace_2017,\n\ttitle = {Laplace current deep level transient spectroscopy measurements of defect states in methylammonium lead bromide single crystals},\n\tvolume = {122},\n\tissn = {0021-8979},\n\turl = {https://doi.org/10.1063/1.4995970},\n\tdoi = {10.1063/1.4995970},\n\tabstract = {We present a measurement of the energies and capture cross-sections of defect states in methylammonium lead bromide (MAPbBr3) single crystals. Using Laplace current deep level transient spectroscopy (I-DLTS), two prominent defects were observed with energies 0.17 eV and 0.20 eV from the band edges, and further I-DLTS measurements confirmed that these two defects are bulk defects. These results show qualitative agreement with theoretical predictions, whereby all of the observed defects behave as traps rather than as generation-recombination centers. These results provide one explanation for the high efficiencies and open-circuit voltages obtained from devices made with lead halide perovskites.},\n\tnumber = {14},\n\turldate = {2023-12-13},\n\tjournal = {Journal of Applied Physics},\n\tauthor = {Rosenberg, John W. and Legodi, Matshisa J. and Rakita, Yevgeny and Cahen, David and Diale, Mmantsae},\n\tmonth = oct,\n\tyear = {2017},\n\tpages = {145701},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/CDFXYART/Rosenberg et al. - 2017 - Laplace current deep level transient spectroscopy .pdf:application/pdf;Snapshot:/Users/yevgenyr/Zotero/storage/XFIRSPD4/Laplace-current-deep-level-transient-spectroscopy.html:text/html},\n}\n\n\n\n We present a measurement of the energies and capture cross-sections of defect states in methylammonium lead bromide (MAPbBr3) single crystals. Using Laplace current deep level transient spectroscopy (I-DLTS), two prominent defects were observed with energies 0.17 eV and 0.20 eV from the band edges, and further I-DLTS measurements confirmed that these two defects are bulk defects. These results show qualitative agreement with theoretical predictions, whereby all of the observed defects behave as traps rather than as generation-recombination centers. These results provide one explanation for the high efficiencies and open-circuit voltages obtained from devices made with lead halide perovskites.\n
\n\n\n\n \n\n \n \n \n \n \n \n Metal to Halide Perovskite (HaP): An Alternative Route to HaP Coating, Directly from Pb(0) or Sn(0) Films.\n \n \n \n \n\n\n \n Rakita, Y.; Gupta, S.; Cahen, D.; and Hodes, G.\n\n\n \n\n\n\n Chemistry of Materials, 29(20): 8620–8629. October 2017.\n Publisher: American Chemical Society\n\n\n\n
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\n\n\n@article{rakita_metal_2017,\n\ttitle = {Metal to {Halide} {Perovskite} ({HaP}): {An} {Alternative} {Route} to {HaP} {Coating}, {Directly} from {Pb}(0) or {Sn}(0) {Films}},\n\tvolume = {29},\n\tissn = {0897-4756},\n\tshorttitle = {Metal to {Halide} {Perovskite} ({HaP})},\n\turl = {https://doi.org/10.1021/acs.chemmater.7b02314},\n\tdoi = {10.1021/acs.chemmater.7b02314},\n\tabstract = {Halide perovskite film-based devices (e.g., solar cells and LEDs) have shown unique device performance. These films are commonly prepared from toxic solutions of metal salts (e.g., Pb2+ in DMF or DMSO). We describe a method to form halide perovskite films by simply reacting metal (Pb or Sn) films with alcoholic solutions of monovalent alkali metal or alkyl ammonium halides, which avoids the use of toxic Pb2+ solutions in the manufacturing step. We show how the morphology of the films can be controlled by variation in reaction parameters and also how mixed halide perovskite films can be prepared. A mechanism for the metal-to-perovskite conversion is suggested. We further show how electrochemically assisted conversion can allow control over the oxidation state of the metal and increase the reaction rate greatly.},\n\tnumber = {20},\n\turldate = {2023-12-13},\n\tjournal = {Chemistry of Materials},\n\tauthor = {Rakita, Yevgeny and Gupta, Satyajit and Cahen, David and Hodes, Gary},\n\tmonth = oct,\n\tyear = {2017},\n\tnote = {Publisher: American Chemical Society},\n\tpages = {8620--8629},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/XN6CLTCQ/Rakita et al. - 2017 - Metal to Halide Perovskite (HaP) An Alternative R.pdf:application/pdf},\n}\n\n\n\n Halide perovskite film-based devices (e.g., solar cells and LEDs) have shown unique device performance. These films are commonly prepared from toxic solutions of metal salts (e.g., Pb2+ in DMF or DMSO). We describe a method to form halide perovskite films by simply reacting metal (Pb or Sn) films with alcoholic solutions of monovalent alkali metal or alkyl ammonium halides, which avoids the use of toxic Pb2+ solutions in the manufacturing step. We show how the morphology of the films can be controlled by variation in reaction parameters and also how mixed halide perovskite films can be prepared. A mechanism for the metal-to-perovskite conversion is suggested. We further show how electrochemically assisted conversion can allow control over the oxidation state of the metal and increase the reaction rate greatly.\n
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\n \n \n\n \n \n \n \n \n \n CH3NH3PbBr3 is not pyroelectric, excluding ferroelectric-enhanced photovoltaic performance.\n \n \n \n \n\n\n \n Rakita, Y.; Meirzadeh, E.; Bendikov, T.; Kalchenko, V.; Lubomirsky, I.; Hodes, G.; Ehre, D.; and Cahen, D.\n\n\n \n\n\n\n APL Materials, 4(5): 051101. May 2016.\n \n\n\n\n
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\n\n\n@article{rakita_ch3nh3pbbr3_2016,\n\ttitle = {{CH3NH3PbBr3} is not pyroelectric, excluding ferroelectric-enhanced photovoltaic performance},\n\tvolume = {4},\n\tissn = {2166-532X},\n\turl = {https://doi.org/10.1063/1.4949760},\n\tdoi = {10.1063/1.4949760},\n\tabstract = {To experimentally (dis)prove ferroelectric effects on the properties of lead-halide perovskites and of solar cells, based on them, we used second-harmonic-generation spectroscopy and the periodic temperature change (Chynoweth) technique to detect the polar nature of methylammonium lead bromide (MAPbBr3). We find that MAPbBr3 is probably centrosymmetric and definitely non-polar; thus, it cannot be ferroelectric. Whenever pyroelectric-like signals were detected, they could be shown to be due to trapped charges, likely at the interface between the metal electrode and the MAPbBr3 semiconductor. These results indicate that the ferroelectric effects do not affect steady-state performance of MAPbBr3 solar cells.},\n\tnumber = {5},\n\turldate = {2023-12-13},\n\tjournal = {APL Materials},\n\tauthor = {Rakita, Yevgeny and Meirzadeh, Elena and Bendikov, Tatyana and Kalchenko, Vyacheslav and Lubomirsky, Igor and Hodes, Gary and Ehre, David and Cahen, David},\n\tmonth = may,\n\tyear = {2016},\n\tpages = {051101},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/TYKFNLP2/Rakita et al. - 2016 - CH3NH3PbBr3 is not pyroelectric, excluding ferroel.pdf:application/pdf},\n}\n\n\n\n To experimentally (dis)prove ferroelectric effects on the properties of lead-halide perovskites and of solar cells, based on them, we used second-harmonic-generation spectroscopy and the periodic temperature change (Chynoweth) technique to detect the polar nature of methylammonium lead bromide (MAPbBr3). We find that MAPbBr3 is probably centrosymmetric and definitely non-polar; thus, it cannot be ferroelectric. Whenever pyroelectric-like signals were detected, they could be shown to be due to trapped charges, likely at the interface between the metal electrode and the MAPbBr3 semiconductor. These results indicate that the ferroelectric effects do not affect steady-state performance of MAPbBr3 solar cells.\n
\n\n\n\n \n\n \n \n \n \n \n \n Conversion of Single Crystalline PbI2 to CH3NH3PbI3: Structural Relations and Transformation Dynamics.\n \n \n \n \n\n\n \n Brenner, T. M.; Rakita, Y.; Orr, Y.; Klein, E.; Feldman, I.; Elbaum, M.; Cahen, D.; and Hodes, G.\n\n\n \n\n\n\n Chemistry of Materials, 28(18): 6501–6510. September 2016.\n Publisher: American Chemical Society\n\n\n\n
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\n\n\n@article{brenner_conversion_2016,\n\ttitle = {Conversion of {Single} {Crystalline} {PbI2} to {CH3NH3PbI3}: {Structural} {Relations} and {Transformation} {Dynamics}},\n\tvolume = {28},\n\tissn = {0897-4756},\n\tshorttitle = {Conversion of {Single} {Crystalline} {PbI2} to {CH3NH3PbI3}},\n\turl = {https://doi.org/10.1021/acs.chemmater.6b01747},\n\tdoi = {10.1021/acs.chemmater.6b01747},\n\tabstract = {The realization of high-quality optoelectronic properties in halide perovskite semiconductors through low-temperature, low energy processing is unprecedented. Understanding the unique aspects of the formation chemistry of these semiconductors is a critical step toward understanding the genesis of high quality material via simple preparation procedures. The toolbox of preparation procedures for halide perovskites grows rapidly. The prototypical reaction is that between lead iodide (PbI2) and methylammonium iodide (CH3NH3I, abbr. MAI) to form the perovskite CH3NH3PbI3 (MAPbI3), which we discuss in this work. We investigate the conversion of small, single-crystalline PbI2 crystallites to MAPbI3 by two commonly used synthesis processes: reaction with MAI in solution or as a vapor. The single crystal nature of the PbI2 precursor allows definitive conclusions to be made about the relationship between the precursors and the final product, illuminating previously unobserved aspects of the reaction process. From in situ photoluminescence microscopy, we find that the reaction in solution begins via isolated nucleation events followed by growth from the nuclei. We observe via X-ray diffraction and morphological characterization that there is a strong orientational and structural relationship between the final stage of the solution-reacted MAPbI3 product and the initial PbI2 crystallite. In all these measurements, we find that the reaction does not proceed below a certain MAI threshold concentration, which allows the first experimental determination of a free energy of formation for a widely used synthetic procedure of ∼0.1 eV. From these conclusions, we present a more detailed hypothesis about the reaction pathway than has yet been proposed: Our results suggest that the reaction in solution begins with a topotactic nucleation event followed by grain growth by dissolution–reconstruction. By similar techniques, we find the reaction via vapor phase produces material lacking a preferred orientation, suggesting the transformation is dominated by a deconstruction–reconstruction process due to the higher thermal energy involved. We also find that the crystal lattice structure of the vapor-reacted material is clearly different from that of the solution-phase reaction due to the temperature conditions of the synthesis.},\n\tnumber = {18},\n\turldate = {2023-12-13},\n\tjournal = {Chemistry of Materials},\n\tauthor = {Brenner, Thomas M. and Rakita, Yevgeny and Orr, Yonatan and Klein, Eugenia and Feldman, Ishay and Elbaum, Michael and Cahen, David and Hodes, Gary},\n\tmonth = sep,\n\tyear = {2016},\n\tnote = {Publisher: American Chemical Society},\n\tpages = {6501--6510},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/XQJPU9TQ/Brenner et al. - 2016 - Conversion of Single Crystalline PbI2 to CH3NH3PbI.pdf:application/pdf},\n}\n\n\n\n The realization of high-quality optoelectronic properties in halide perovskite semiconductors through low-temperature, low energy processing is unprecedented. Understanding the unique aspects of the formation chemistry of these semiconductors is a critical step toward understanding the genesis of high quality material via simple preparation procedures. The toolbox of preparation procedures for halide perovskites grows rapidly. The prototypical reaction is that between lead iodide (PbI2) and methylammonium iodide (CH3NH3I, abbr. MAI) to form the perovskite CH3NH3PbI3 (MAPbI3), which we discuss in this work. We investigate the conversion of small, single-crystalline PbI2 crystallites to MAPbI3 by two commonly used synthesis processes: reaction with MAI in solution or as a vapor. The single crystal nature of the PbI2 precursor allows definitive conclusions to be made about the relationship between the precursors and the final product, illuminating previously unobserved aspects of the reaction process. From in situ photoluminescence microscopy, we find that the reaction in solution begins via isolated nucleation events followed by growth from the nuclei. We observe via X-ray diffraction and morphological characterization that there is a strong orientational and structural relationship between the final stage of the solution-reacted MAPbI3 product and the initial PbI2 crystallite. In all these measurements, we find that the reaction does not proceed below a certain MAI threshold concentration, which allows the first experimental determination of a free energy of formation for a widely used synthetic procedure of ∼0.1 eV. From these conclusions, we present a more detailed hypothesis about the reaction pathway than has yet been proposed: Our results suggest that the reaction in solution begins with a topotactic nucleation event followed by grain growth by dissolution–reconstruction. By similar techniques, we find the reaction via vapor phase produces material lacking a preferred orientation, suggesting the transformation is dominated by a deconstruction–reconstruction process due to the higher thermal energy involved. We also find that the crystal lattice structure of the vapor-reacted material is clearly different from that of the solution-phase reaction due to the temperature conditions of the synthesis.\n
\n\n\n\n \n\n \n \n \n \n \n \n Low-Temperature Solution-Grown CsPbBr3 Single Crystals and Their Characterization.\n \n \n \n \n\n\n \n Rakita, Y.; Kedem, N.; Gupta, S.; Sadhanala, A.; Kalchenko, V.; Böhm, M. L.; Kulbak, M.; Friend, R. H.; Cahen, D.; and Hodes, G.\n\n\n \n\n\n\n Crystal Growth & Design, 16(10): 5717–5725. October 2016.\n Publisher: American Chemical Society\n\n\n\n
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\n\n\n@article{rakita_low-temperature_2016,\n\ttitle = {Low-{Temperature} {Solution}-{Grown} {CsPbBr3} {Single} {Crystals} and {Their} {Characterization}},\n\tvolume = {16},\n\tissn = {1528-7483},\n\turl = {https://doi.org/10.1021/acs.cgd.6b00764},\n\tdoi = {10.1021/acs.cgd.6b00764},\n\tabstract = {Cesium lead bromide (CsPbBr3) was recently introduced as a potentially high performance thin-film halide perovskite (HaP) material for optoelectronics, including photovoltaics, significantly more stable than MAPbBr3 (MA = CH3NH3+). Because of the importance of single crystals to study relevant material properties per se, crystals grown under conditions comparable to those used for preparing thin films, i.e., low-temperature solution-based growth, are needed. We show here two simple ways, antisolvent-vapor saturation or heating a solution containing retrograde soluble CsPbBr3, to grow single crystals of CsPbBr3 from a precursor solution, treated with acetonitrile (MeCN) or methanol (MeOH). The precursor solutions are stable for at least several months. Millimeter-sized crystals are grown without crystal-seeding and can provide a 100\\% yield of CsPbBr3 perovskite crystals, avoiding a CsBr-rich (or PbBr2-rich) composition, which is often present alongside the perovskite phase. Further growth is demonstrated to be possible with crystal seeding. The crystals are characterized in several ways, including first results of charge carrier lifetime (30 ns) and an upper-limit of the Urbach energy (19 meV). As the crystals are grown from a polar aprotic solvent (DMSO), which is similar to those used to grow hybrid organic–inorganic HaP crystals, this may allow growing mixed (organic and inorganic) monovalent cation HaP crystals.},\n\tnumber = {10},\n\turldate = {2023-12-13},\n\tjournal = {Crystal Growth \\& Design},\n\tauthor = {Rakita, Yevgeny and Kedem, Nir and Gupta, Satyajit and Sadhanala, Aditya and Kalchenko, Vyacheslav and Böhm, Marcus L. and Kulbak, Michael and Friend, Richard H. and Cahen, David and Hodes, Gary},\n\tmonth = oct,\n\tyear = {2016},\n\tnote = {Publisher: American Chemical Society},\n\tpages = {5717--5725},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/SYAALM62/Rakita et al. - 2016 - Low-Temperature Solution-Grown CsPbBr3 Single Crys.pdf:application/pdf},\n}\n\n\n\n Cesium lead bromide (CsPbBr3) was recently introduced as a potentially high performance thin-film halide perovskite (HaP) material for optoelectronics, including photovoltaics, significantly more stable than MAPbBr3 (MA = CH3NH3+). Because of the importance of single crystals to study relevant material properties per se, crystals grown under conditions comparable to those used for preparing thin films, i.e., low-temperature solution-based growth, are needed. We show here two simple ways, antisolvent-vapor saturation or heating a solution containing retrograde soluble CsPbBr3, to grow single crystals of CsPbBr3 from a precursor solution, treated with acetonitrile (MeCN) or methanol (MeOH). The precursor solutions are stable for at least several months. Millimeter-sized crystals are grown without crystal-seeding and can provide a 100% yield of CsPbBr3 perovskite crystals, avoiding a CsBr-rich (or PbBr2-rich) composition, which is often present alongside the perovskite phase. Further growth is demonstrated to be possible with crystal seeding. The crystals are characterized in several ways, including first results of charge carrier lifetime (30 ns) and an upper-limit of the Urbach energy (19 meV). As the crystals are grown from a polar aprotic solvent (DMSO), which is similar to those used to grow hybrid organic–inorganic HaP crystals, this may allow growing mixed (organic and inorganic) monovalent cation HaP crystals.\n
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\n\n \n \n 2015\n \n \n (1)\n \n \n
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\n \n \n\n \n \n \n \n \n \n Mechanical properties of APbX3 (A = Cs or CH3NH3; X = I or Br) perovskite single crystals.\n \n \n \n \n\n\n \n Rakita, Y.; Cohen, S. R.; Kedem, N. K.; Hodes, G.; and Cahen, D.\n\n\n \n\n\n\n MRS Communications, 5(4): 623–629. December 2015.\n Publisher: Cambridge University Press\n\n\n\n
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\n\n\n@article{rakita_mechanical_2015,\n\ttitle = {Mechanical properties of {APbX3} ({A} = {Cs} or {CH3NH3}; {X} = {I} or {Br}) perovskite single crystals},\n\tvolume = {5},\n\tissn = {2159-6859, 2159-6867},\n\turl = {https://www.cambridge.org/core/journals/mrs-communications/article/mechanical-properties-of-apbx3-a-cs-or-ch3nh3-xi-or-br-perovskite-single-crystals/87CE3153864BEC492460ADF634F85F0E},\n\tdoi = {10.1557/mrc.2015.69},\n\tabstract = {, The remarkable optoelectronic and especially photovoltaic performance of hybrid organic–inorganic perovskite (HOIP) materials drives efforts to connect materials properties to this performance. From nano-indentation experiments on solution-grown single crystals we obtain elastic modulus and nano-hardness values of APbX3 (A = Cs, CH3NH3; X = I, Br). The Young's moduli are {\\textasciitilde}14, 19.5, and 16 GPa, for CH3NH3PbI3, CH3NH3PbBr3, and CsPbBr3, respectively, lending credence to theoretically calculated values. We discuss the possible relevance of our results to suggested “self-healing”, ion diffusion, and ease of manufacturing. Using our results, together with literature data on elastic moduli, we classified HOIPs amongst the relevant material groups, based on their elastomechanical properties.},\n\tlanguage = {en},\n\tnumber = {4},\n\turldate = {2023-12-13},\n\tjournal = {MRS Communications},\n\tauthor = {Rakita, Yevgeny and Cohen, Sidney R. and Kedem, Nir Klein and Hodes, Gary and Cahen, David},\n\tmonth = dec,\n\tyear = {2015},\n\tnote = {Publisher: Cambridge University Press},\n\tpages = {623--629},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/AMZ5QLUF/Rakita et al. - 2015 - Mechanical properties of APbX3 (A = Cs or CH3NH3\\; .pdf:application/pdf},\n}\n\n\n\n , The remarkable optoelectronic and especially photovoltaic performance of hybrid organic–inorganic perovskite (HOIP) materials drives efforts to connect materials properties to this performance. From nano-indentation experiments on solution-grown single crystals we obtain elastic modulus and nano-hardness values of APbX3 (A = Cs, CH3NH3; X = I, Br). The Young's moduli are ~14, 19.5, and 16 GPa, for CH3NH3PbI3, CH3NH3PbBr3, and CsPbBr3, respectively, lending credence to theoretically calculated values. We discuss the possible relevance of our results to suggested “self-healing”, ion diffusion, and ease of manufacturing. Using our results, together with literature data on elastic moduli, we classified HOIPs amongst the relevant material groups, based on their elastomechanical properties.\n
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\n\n\n\n\n \n \n 2014\n \n \n (1)\n \n \n
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\n \n \n\n \n \n \n \n \n \n Electrostatic Potential of Polyelectrolyte Molecules Grafted on Charged Surfaces: A Poisson-Boltzmann Model.\n \n \n \n \n\n\n \n Rakita, Y.; Golodnitsky, D.; and Natan, A.\n\n\n \n\n\n\n Journal of The Electrochemical Society, 161(8): E3049. March 2014.\n Publisher: IOP Publishing\n\n\n\n
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\n\n\n\n@article{rakita_electrostatic_2014,\n\ttitle = {Electrostatic {Potential} of {Polyelectrolyte} {Molecules} {Grafted} on {Charged} {Surfaces}: {A} {Poisson}-{Boltzmann} {Model}},\n\tvolume = {161},\n\tissn = {1945-7111},\n\tshorttitle = {Electrostatic {Potential} of {Polyelectrolyte} {Molecules} {Grafted} on {Charged} {Surfaces}},\n\turl = {https://iopscience.iop.org/article/10.1149/2.008408jes/meta},\n\tdoi = {10.1149/2.008408jes},\n\tlanguage = {en},\n\tnumber = {8},\n\turldate = {2023-12-13},\n\tjournal = {Journal of The Electrochemical Society},\n\tauthor = {Rakita, Y. and Golodnitsky, D. and Natan, A.},\n\tmonth = mar,\n\tyear = {2014},\n\tnote = {Publisher: IOP Publishing},\n\tpages = {E3049},\n\tfile = {Full Text PDF:/Users/yevgenyr/Zotero/storage/9MKXXX67/Rakita et al. - 2014 - Electrostatic Potential of Polyelectrolyte Molecul.pdf:application/pdf},\n}\n\n\n