@article{
 title = {Electronic Coupling in Metallophthalocyanine–Transition Metal Dichalcogenide Mixed-Dimensional Heterojunctions},
 type = {article},
 year = {2019},
 pages = {4183-4190},
 volume = {13},
 websites = {https://doi.org/10.1021/acsnano.8b09166},
 month = {4},
 id = {4f035ac3-98d9-38d6-bd6f-240067bfb376},
 created = {2020-12-18T06:00:27.177Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:27.177Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 private_publication = {false},
 abstract = {Mixed-dimensional heterojunctions, such as zero-dimensional (0D) organic molecules deposited on two-dimensional (2D) transition metal dichalcogenides (TMDCs), often exhibit interfacial effects that enhance the properties of the individual constituent layers. Here we report a systematic study of interfacial charge transfer in metallophthalocyanine (MPc) – MoS2 heterojunctions using optical absorption and Raman spectroscopy to elucidate M core (M = first row transition metal), MoS2 layer number, and excitation wavelength effects. Observed phenomena include the emergence of heterojunction-specific optical absorption transitions and strong Raman enhancement that depends on the M identity. In addition, the Raman enhancement is tunable by excitation laser wavelength and MoS2 layer number, ultimately reaching a maximum enhancement factor of 30x relative to SiO2 substrates. These experimental results, combined with density functional theory (DFT) calculations, indicate strong coupling between nonfrontier MPc orbitals and the MoS2 band structure as well as charge transfer across the heterojunction interface that varies as a function of the MPc electronic structure.},
 bibtype = {article},
 author = {Amsterdam, Samuel H and Stanev, Teodor K and Zhou, Qunfei and Lou, Alexander J.-T. and Bergeron, Hadallia and Darancet, Pierre and Hersam, Mark C and Stern, Nathaniel P and Marks, Tobin J},
 doi = {10.1021/acsnano.8b09166},
 journal = {ACS Nano},
 number = {4}
}

Mixed-dimensional heterojunctions, such as zero-dimensional (0D) organic molecules deposited on two-dimensional (2D) transition metal dichalcogenides (TMDCs), often exhibit interfacial effects that enhance the properties of the individual constituent layers. Here we report a systematic study of interfacial charge transfer in metallophthalocyanine (MPc) – MoS2 heterojunctions using optical absorption and Raman spectroscopy to elucidate M core (M = first row transition metal), MoS2 layer number, and excitation wavelength effects. Observed phenomena include the emergence of heterojunction-specific optical absorption transitions and strong Raman enhancement that depends on the M identity. In addition, the Raman enhancement is tunable by excitation laser wavelength and MoS2 layer number, ultimately reaching a maximum enhancement factor of 30x relative to SiO2 substrates. These experimental results, combined with density functional theory (DFT) calculations, indicate strong coupling between nonfrontier MPc orbitals and the MoS2 band structure as well as charge transfer across the heterojunction interface that varies as a function of the MPc electronic structure.

@article{
 title = {Electrical Control of Circular Photogalvanic Spin-Valley Photocurrent in a Monolayer Semiconductor},
 type = {article},
 year = {2019},
 pages = {3334-3341},
 volume = {11},
 websites = {https://pubs.acs.org/doi/10.1021/acsami.8b17476},
 month = {1},
 id = {82384993-5156-3cc1-8fa4-992508645961},
 created = {2020-12-18T06:00:27.779Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:27.779Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 bibtype = {article},
 author = {Liu, Lei and Lenferink, Erik J and Wei, Guohua and Stanev, Teodor K and Speiser, Nathaniel and Stern, Nathaniel P},
 doi = {10.1021/acsami.8b17476},
 journal = {ACS Applied Materials & Interfaces},
 number = {3}
}

@article{
 title = {Intrinsic Transport in 2D Heterostructures Mediated through h-BN Tunneling Contacts},
 type = {article},
 year = {2018},
 pages = {2990-2998},
 volume = {18},
 websites = {https://doi.org/10.1021/acs.nanolett.8b00444},
 month = {5},
 id = {3e456ae3-2b8b-3038-8045-8d2a409360ee},
 created = {2020-12-18T06:00:28.390Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:28.390Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 private_publication = {false},
 abstract = {Understanding the electronic transport of monolayer transition metal dichalcogenides (TMDs) and their heterostructures is complicated by the difficulty in achieving electrical contacts that do not perturb the material. Typically, metal deposition on monolayer TMDs leads to hybridization between the TMD and the metal, which produces Schottky barriers at the metal/semiconductor interface. In this work, we apply the recently reported hexagonal boron nitride (h-BN) tunnel contact scheme to probe the junction characteristics of a lateral TMD heterostructure grown via chemical vapor deposition. We first measure the electronic properties across the junction before elucidating optoelectronic generation mechanisms via scanning photocurrent microscopy. We find that the rectification ratio measured using the encapsulated, tunnel contact scheme is almost 2 orders of magnitude smaller than that observed via conventional metal contact geometry, which implies that the metal/semiconductor Schottky barriers play large roles in this aspect. Furthermore, we find that both the photovoltaic as well as hot carrier generation effects are dominant mechanisms driving photoresponse, depending on the external biasing conditions. This work is the first time that this encapsulation scheme has been applied to lateral heterostructures and serves as a reference for future electronic measurements on this material. It also simultaneously serves as a framework to more accurately assess the electronic transport characteristics of 2D heterostructures and better inform future device architectures.},
 bibtype = {article},
 author = {Murthy, Akshay A and Stanev, Teodor K and Cain, Jeffrey D and Hao, Shiqiang and LaMountain, Trevor and Kim, Sungkyu and Speiser, Nathaniel and Watanabe, Kenji and Taniguchi, Takashi and Wolverton, Chris and Stern, Nathaniel P and Dravid, Vinayak P},
 doi = {10.1021/acs.nanolett.8b00444},
 journal = {Nano Letters},
 number = {5}
}

Understanding the electronic transport of monolayer transition metal dichalcogenides (TMDs) and their heterostructures is complicated by the difficulty in achieving electrical contacts that do not perturb the material. Typically, metal deposition on monolayer TMDs leads to hybridization between the TMD and the metal, which produces Schottky barriers at the metal/semiconductor interface. In this work, we apply the recently reported hexagonal boron nitride (h-BN) tunnel contact scheme to probe the junction characteristics of a lateral TMD heterostructure grown via chemical vapor deposition. We first measure the electronic properties across the junction before elucidating optoelectronic generation mechanisms via scanning photocurrent microscopy. We find that the rectification ratio measured using the encapsulated, tunnel contact scheme is almost 2 orders of magnitude smaller than that observed via conventional metal contact geometry, which implies that the metal/semiconductor Schottky barriers play large roles in this aspect. Furthermore, we find that both the photovoltaic as well as hot carrier generation effects are dominant mechanisms driving photoresponse, depending on the external biasing conditions. This work is the first time that this encapsulation scheme has been applied to lateral heterostructures and serves as a reference for future electronic measurements on this material. It also simultaneously serves as a framework to more accurately assess the electronic transport characteristics of 2D heterostructures and better inform future device architectures.

@article{
 title = {Environmental engineering of transition metal dichalcogenide optoelectronics},
 type = {article},
 year = {2018},
 pages = {138114},
 volume = {13},
 websites = {https://doi.org/10.1007/s11467-018-0795-x},
 month = {6},
 id = {4c476aa5-892f-3599-ade3-0c9427d5b4d0},
 created = {2020-12-18T06:00:29.041Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:29.041Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 abstract = {The explosion of interest in two-dimensional van der Waals materials has been in many ways driven by their layered geometry. This feature makes possible numerous avenues for assembling and manipulating the optical and electronic properties of these materials. In the specific case of monolayer transition metal dichalcogenide semiconductors, the direct band gap combined with the flexibility for manipulation of layers has made this class of materials promising for optoelectronics. Here, we review the properties of these layered materials and the various means of engineering these properties for optoelectronics. We summarize approaches for control that modify their structural and chemical environment, and we give particular detail on the integration of these materials into engineered optical fields to control their optical characteristics. This combination of controllability from their layered surface structure and photonic environment provide an expansive landscape for novel optoelectronic phenomena.},
 bibtype = {article},
 author = {LaMountain, Trevor and Lenferink, Erik J and Chen, Yen-Jung and Stanev, Teodor K and Stern, Nathaniel P},
 doi = {10.1007/s11467-018-0795-x},
 journal = {Frontiers of Physics},
 number = {4}
}

The explosion of interest in two-dimensional van der Waals materials has been in many ways driven by their layered geometry. This feature makes possible numerous avenues for assembling and manipulating the optical and electronic properties of these materials. In the specific case of monolayer transition metal dichalcogenide semiconductors, the direct band gap combined with the flexibility for manipulation of layers has made this class of materials promising for optoelectronics. Here, we review the properties of these layered materials and the various means of engineering these properties for optoelectronics. We summarize approaches for control that modify their structural and chemical environment, and we give particular detail on the integration of these materials into engineered optical fields to control their optical characteristics. This combination of controllability from their layered surface structure and photonic environment provide an expansive landscape for novel optoelectronic phenomena.

@article{
 title = {Valley-selective optical Stark effect probed by Kerr rotation},
 type = {article},
 year = {2018},
 pages = {45307},
 volume = {97},
 websites = {https://link.aps.org/doi/10.1103/PhysRevB.97.045307},
 month = {1},
 id = {2dc7b1d3-cdae-3e26-ac57-29fd0517567e},
 created = {2020-12-18T06:00:29.691Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:29.691Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 private_publication = {false},
 abstract = {The ability to monitor and control distinct states is at the heart of emerging quantum technologies. The valley pseudospin in transition metal dichalcogenide (TMDC) monolayers is a promising degree of freedom for such control, with the optical Stark effect allowing for valley-selective manipulation of energy levels in WS2 and WSe2 using ultrafast optical pulses. Despite these advances, understanding of valley-sensitive optical Stark shifts in TMDCs has been limited by reflectance-based detection methods where the signal is small and prone to background effects. More sensitive polarization-based spectroscopy is required to better probe ultrafast Stark shifts for all-optical manipulation of valley energy levels. Here, we show time-resolved Kerr rotation to be a more sensitive probe of the valley-selective optical Stark effect in monolayer TMDCs. Compared to the established time-resolved reflectance methods, Kerr rotation is less sensitive to background effects. Kerr rotation provides a fivefold improvement in the signal-to-noise ratio of the Stark effect optical signal and a more precise estimate of the energy shift. This increased sensitivity allows for observation of an optical Stark shift in monolayer MoS2 that exhibits both valley and energy selectivity, demonstrating the promise of this method for investigating this effect in other layered materials and heterostructures.},
 bibtype = {article},
 author = {LaMountain, Trevor and Bergeron, Hadallia and Balla, Itamar and Stanev, Teodor K and Hersam, Mark C and Stern, Nathaniel P},
 doi = {10.1103/PhysRevB.97.045307},
 journal = {Physical Review B},
 number = {4}
}

The ability to monitor and control distinct states is at the heart of emerging quantum technologies. The valley pseudospin in transition metal dichalcogenide (TMDC) monolayers is a promising degree of freedom for such control, with the optical Stark effect allowing for valley-selective manipulation of energy levels in WS2 and WSe2 using ultrafast optical pulses. Despite these advances, understanding of valley-sensitive optical Stark shifts in TMDCs has been limited by reflectance-based detection methods where the signal is small and prone to background effects. More sensitive polarization-based spectroscopy is required to better probe ultrafast Stark shifts for all-optical manipulation of valley energy levels. Here, we show time-resolved Kerr rotation to be a more sensitive probe of the valley-selective optical Stark effect in monolayer TMDCs. Compared to the established time-resolved reflectance methods, Kerr rotation is less sensitive to background effects. Kerr rotation provides a fivefold improvement in the signal-to-noise ratio of the Stark effect optical signal and a more precise estimate of the energy shift. This increased sensitivity allows for observation of an optical Stark shift in monolayer MoS2 that exhibits both valley and energy selectivity, demonstrating the promise of this method for investigating this effect in other layered materials and heterostructures.

@article{
 title = {Control of interlayer physics in 2H transition metal dichalcogenides},
 type = {article},
 year = {2017},
 pages = {224302},
 volume = {122},
 websites = {http://aip.scitation.org/doi/10.1063/1.5005958},
 month = {12},
 id = {6bf00a5e-ff1f-3b53-8d09-d761f643e580},
 created = {2020-12-18T06:00:30.340Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:30.340Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 bibtype = {article},
 author = {Wang, Kuang-Chung and Stanev, Teodor K and Valencia, Daniel and Charles, James and Henning, Alex and Sangwan, Vinod K and Lahiri, Aritra and Mejia, Daniel and Sarangapani, Prasad and Povolotskyi, Michael and Afzalian, Aryan and Maassen, Jesse and Klimeck, Gerhard and Hersam, Mark C and Lauhon, Lincoln J and Stern, Nathaniel P and Kubis, Tillmann},
 doi = {10.1063/1.5005958},
 journal = {Journal of Applied Physics},
 number = {22}
}

@article{
 title = {Width-dependent Photoluminescence and Anisotropic Raman Spectroscopy from Monolayer MoS$_2$ Nanoribbons},
 type = {article},
 year = {2017},
 keywords = {Condensed Matter - Mesoscale and Nanoscale Physics},
 websites = {http://arxiv.org/abs/1709.04001},
 month = {9},
 id = {59298e6e-cc96-33b4-b471-dbf8db4c7832},
 created = {2020-12-18T06:00:30.994Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:30.994Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 private_publication = {false},
 abstract = {Single layers of transition metal dichalcogenides such as MoS$_2$ are direct bandgap semiconductors with optical and electronic properties distinct from multilayers due to strong vertical confinement. Despite the fundamental monolayer limit of thickness, the electronic structure of isolated layers can be further tailored with lateral degrees of freedom in nanostructures such as quantum dots or nanoribbons. Although one-dimensionally confined monolayer semiconductors are predicted to have interesting size- and edge-dependent properties useful for spintronics applications, experiments on the opto-electronic features of monolayer transition metal dichalcogenide nanoribbons is limited. We use nanolithography to create monolayer MoS$_2$ nanoribbons with lateral sizes down to 20 nm. The Raman spectra show polarization anisotropy and size-dependent intensity. The nanoribbons prepared with this technique show reduced susceptibility to edge defects and emit photoluminescence with size-dependent energy that can be understood from a phenomenological model. Fabrication of monolayer nanoribbons with strong exciton emission can facilitate exploration of low-dimensional opto-electronic devices with controllable properties.},
 bibtype = {article},
 author = {Wei, Guohua and Lenferink, Erik J and Czaplewski, David A and Stern, Nathaniel P},
 journal = {arXiv:1709.04001 [cond-mat]}
}

Single layers of transition metal dichalcogenides such as MoS$_2$ are direct bandgap semiconductors with optical and electronic properties distinct from multilayers due to strong vertical confinement. Despite the fundamental monolayer limit of thickness, the electronic structure of isolated layers can be further tailored with lateral degrees of freedom in nanostructures such as quantum dots or nanoribbons. Although one-dimensionally confined monolayer semiconductors are predicted to have interesting size- and edge-dependent properties useful for spintronics applications, experiments on the opto-electronic features of monolayer transition metal dichalcogenide nanoribbons is limited. We use nanolithography to create monolayer MoS$_2$ nanoribbons with lateral sizes down to 20 nm. The Raman spectra show polarization anisotropy and size-dependent intensity. The nanoribbons prepared with this technique show reduced susceptibility to edge defects and emit photoluminescence with size-dependent energy that can be understood from a phenomenological model. Fabrication of monolayer nanoribbons with strong exciton emission can facilitate exploration of low-dimensional opto-electronic devices with controllable properties.

@article{
 title = {Valley-polarized exciton–polaritons in a monolayer semiconductor},
 type = {article},
 year = {2017},
 keywords = {stern:2D},
 pages = {431-435},
 volume = {11},
 websites = {https://www.nature.com/articles/nphoton.2017.86},
 month = {7},
 id = {a496682f-7ce3-3ea8-8be3-69f17de87c57},
 created = {2020-12-18T06:00:31.589Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:31.589Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 abstract = {Exploitation of the valley electronic structure of transition metal dichalcogenides with exciton–polaritons is an elusive challenge. Now, valley-polarized exciton–polaritons in monolayers of MoS2 have been demonstrated.},
 bibtype = {article},
 author = {Chen, Yen-Jung and Cain, Jeffrey D and Stanev, Teodor K and Dravid, Vinayak P and Stern, Nathaniel P},
 doi = {10.1038/nphoton.2017.86},
 journal = {Nature Photonics},
 number = {7}
}

Exploitation of the valley electronic structure of transition metal dichalcogenides with exciton–polaritons is an elusive challenge. Now, valley-polarized exciton–polaritons in monolayers of MoS2 have been demonstrated.

@article{
 title = {Directional emission from dye-functionalized plasmonic DNA superlattice microcavities},
 type = {article},
 year = {2017},
 keywords = {DNA programmable assembly,anisotropic 3D microcavity,directional emission,fluorescence enhancement,nanoparticle surface plasmon},
 pages = {457-461},
 volume = {114},
 websites = {https://www.pnas.org/content/114/3/457},
 month = {1},
 id = {f9870c85-88fe-36ad-bcad-7dc892d34596},
 created = {2020-12-18T06:00:32.254Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:32.254Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 abstract = {Three-dimensional plasmonic superlattice microcavities, made from programmable atom equivalents comprising gold nanoparticles functionalized with DNA, are used as a testbed to study directional light emission. DNA-guided nanoparticle colloidal crystallization allows for the formation of micrometer-scale single-crystal body-centered cubic gold nanoparticle superlattices, with dye molecules coupled to the DNA strands that link the particles together, in the form of a rhombic dodecahedron. Encapsulation in silica allows one to create robust architectures with the plasmonically active particles and dye molecules fixed in space. At the micrometer scale, the anisotropic rhombic dodecahedron crystal habit couples with photonic modes to give directional light emission. At the nanoscale, the interaction between the dye dipoles and surface plasmons can be finely tuned by coupling the dye molecules to specific sites of the DNA particle-linker strands, thereby modulating dye–nanoparticle distance (three different positions are studied). The ability to control dye position with subnanometer precision allows one to systematically tune plasmon–excition interaction strength and decay lifetime, the results of which have been supported by electrodynamics calculations that span length scales from nanometers to micrometers. The unique ability to control surface plasmon/exciton interactions within such superlattice microcavities will catalyze studies involving quantum optics, plasmon laser physics, strong coupling, and nonlinear phenomena.},
 bibtype = {article},
 author = {Park, Daniel J and Ku, Jessie C and Sun, Lin and Lethiec, Clotilde M and Stern, Nathaniel P and Schatz, George C and Mirkin, Chad A},
 doi = {10.1073/pnas.1619802114},
 journal = {Proceedings of the National Academy of Sciences},
 number = {3}
}

Three-dimensional plasmonic superlattice microcavities, made from programmable atom equivalents comprising gold nanoparticles functionalized with DNA, are used as a testbed to study directional light emission. DNA-guided nanoparticle colloidal crystallization allows for the formation of micrometer-scale single-crystal body-centered cubic gold nanoparticle superlattices, with dye molecules coupled to the DNA strands that link the particles together, in the form of a rhombic dodecahedron. Encapsulation in silica allows one to create robust architectures with the plasmonically active particles and dye molecules fixed in space. At the micrometer scale, the anisotropic rhombic dodecahedron crystal habit couples with photonic modes to give directional light emission. At the nanoscale, the interaction between the dye dipoles and surface plasmons can be finely tuned by coupling the dye molecules to specific sites of the DNA particle-linker strands, thereby modulating dye–nanoparticle distance (three different positions are studied). The ability to control dye position with subnanometer precision allows one to systematically tune plasmon–excition interaction strength and decay lifetime, the results of which have been supported by electrodynamics calculations that span length scales from nanometers to micrometers. The unique ability to control surface plasmon/exciton interactions within such superlattice microcavities will catalyze studies involving quantum optics, plasmon laser physics, strong coupling, and nonlinear phenomena.

@article{
 title = {Size-tunable Lateral Confinement in Monolayer Semiconductors},
 type = {article},
 year = {2017},
 pages = {1-8},
 volume = {7},
 websites = {https://www.nature.com/articles/s41598-017-03594-z},
 month = {6},
 id = {2b04345c-fc2a-359a-bafa-d66b9b1f5723},
 created = {2020-12-18T06:00:33.171Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:33.171Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 abstract = {Three-dimensional confinement allows semiconductor quantum dots to exhibit size-tunable electronic and optical properties that enable a wide range of opto-electronic applications from displays, solar cells and bio-medical imaging to single-electron devices. Additional modalities such as spin and valley properties in monolayer transition metal dichalcogenides provide further degrees of freedom requisite for information processing and spintronics. In nanostructures, however, spatial confinement can cause hybridization that inhibits the robustness of these emergent properties. Here, we show that laterally-confined excitons in monolayer MoS2 nanodots can be created through top-down nanopatterning with controlled size tunability. Unlike chemically-exfoliated monolayer nanoparticles, the lithographically patterned monolayer semiconductor nanodots down to a radius of 15 nm exhibit the same valley polarization as in a continuous monolayer sheet. The inherited bulk spin and valley properties, the size dependence of excitonic energies, and the ability to fabricate MoS2 nanostructures using semiconductor-compatible processing suggest that monolayer semiconductor nanodots have potential to be multimodal building blocks of integrated optoelectronics and spintronics systems.},
 bibtype = {article},
 author = {Wei, Guohua and Czaplewski, David A and Lenferink, Erik J and Stanev, Teodor K and Jung, Il Woong and Stern, Nathaniel P},
 doi = {10.1038/s41598-017-03594-z},
 journal = {Scientific Reports},
 number = {1}
}

Three-dimensional confinement allows semiconductor quantum dots to exhibit size-tunable electronic and optical properties that enable a wide range of opto-electronic applications from displays, solar cells and bio-medical imaging to single-electron devices. Additional modalities such as spin and valley properties in monolayer transition metal dichalcogenides provide further degrees of freedom requisite for information processing and spintronics. In nanostructures, however, spatial confinement can cause hybridization that inhibits the robustness of these emergent properties. Here, we show that laterally-confined excitons in monolayer MoS2 nanodots can be created through top-down nanopatterning with controlled size tunability. Unlike chemically-exfoliated monolayer nanoparticles, the lithographically patterned monolayer semiconductor nanodots down to a radius of 15 nm exhibit the same valley polarization as in a continuous monolayer sheet. The inherited bulk spin and valley properties, the size dependence of excitonic energies, and the ability to fabricate MoS2 nanostructures using semiconductor-compatible processing suggest that monolayer semiconductor nanodots have potential to be multimodal building blocks of integrated optoelectronics and spintronics systems.

@article{
 title = {Photonic ring resonator filters for astronomical OH suppression},
 type = {article},
 year = {2017},
 pages = {15868},
 volume = {25},
 websites = {https://www.osapublishing.org/abstract.cfm?URI=oe-25-14-15868},
 month = {7},
 id = {0fa37fd1-da28-3591-8da3-7df61dc72e9c},
 created = {2020-12-18T06:00:36.676Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:36.676Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 bibtype = {article},
 author = {Ellis, S C and Kuhlmann, S and Kuehn, K and Spinka, H and Underwood, D and Gupta, R R and Ocola, L E and Liu, P and Wei, G and Stern, N P and Bland-Hawthorn, J and Tuthill, P},
 doi = {10.1364/OE.25.015868},
 journal = {Optics Express},
 number = {14}
}

@inproceedings{
 title = {Astrophotonics: the application of photonic technology to astronomy},
 type = {inproceedings},
 year = {2017},
 keywords = {stern:astro},
 pages = {102420O},
 volume = {10242},
 websites = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10242/102420O/Astrophotonics-the-application-of-photonic-technology-to-astronomy/10.1117/12.2265958.short},
 month = {5},
 publisher = {International Society for Optics and Photonics},
 id = {1ac4b692-0bc2-3503-8f05-eac3ee1b3d17},
 created = {2020-12-18T06:00:38.127Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:38.127Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {inproceedings},
 short_title = {Astrophotonics},
 private_publication = {false},
 abstract = {Integrated optics has the potential to play a transformative role in astronomical instrumentation. It has already made a significant impact in the field of optical interferometry, through the use of planar waveguide arrays for beam combination and phase-shifting. Additionally, the potential benefits of micro-spectrographs based on array waveguide gratings have also been demonstrated. br/ br/ Here we examine a new application of integrated optics, using ring resonators as notch filters to remove the signal from atmospheric OH emission lines from astronomical spectra. We also briefly discuss their use as frequency combs for wavelength calibration and as drop filters for Doppler planet searches. We discuss the theoretical requirements for ring resonators for OH suppression. We find that small radius (< 10 μm), high index contrast (Si or Si_3N_4) rings are necessary to provide an adequate free spectral range. The suppression depth, resolving power, and throughput for efficient OH suppression can be realised with critically coupled rings with high self-coupling coefficients. br/ br/ We report on preliminary laboratory tests of our Si and Si3N4 rings and give details of their fabrication. We demonstrate high self-coupling coefficients (> 0:9) and good control over the free spectral range and wavelength separation of multi-ring devices. Current devices have Q ≈ 4000 and ≈ 10 dB suppression, which should be improved through further optimisation of the coupling coefficients. The overall prospects for the use of ring resonators in astronomical instruments is promising, provided efficient fibre-chip coupling can be achieved.},
 bibtype = {inproceedings},
 author = {Ellis, S C and Kuhlmann, S and Kuehn, K and Spinka, H and Underwood, D and Gupta, R R and Ocola, L and Liu, P and Wei, G and Stern, Nathaniel P and Bland-Hawthorn, J and Tuthill, P},
 doi = {10.1117/12.2265958},
 booktitle = {Integrated Optics: Physics and Simulations III}
}

Integrated optics has the potential to play a transformative role in astronomical instrumentation. It has already made a significant impact in the field of optical interferometry, through the use of planar waveguide arrays for beam combination and phase-shifting. Additionally, the potential benefits of micro-spectrographs based on array waveguide gratings have also been demonstrated. br/ br/ Here we examine a new application of integrated optics, using ring resonators as notch filters to remove the signal from atmospheric OH emission lines from astronomical spectra. We also briefly discuss their use as frequency combs for wavelength calibration and as drop filters for Doppler planet searches. We discuss the theoretical requirements for ring resonators for OH suppression. We find that small radius (< 10 μm), high index contrast (Si or Si_3N_4) rings are necessary to provide an adequate free spectral range. The suppression depth, resolving power, and throughput for efficient OH suppression can be realised with critically coupled rings with high self-coupling coefficients. br/ br/ We report on preliminary laboratory tests of our Si and Si3N4 rings and give details of their fabrication. We demonstrate high self-coupling coefficients (> 0:9) and good control over the free spectral range and wavelength separation of multi-ring devices. Current devices have Q ≈ 4000 and ≈ 10 dB suppression, which should be improved through further optimisation of the coupling coefficients. The overall prospects for the use of ring resonators in astronomical instruments is promising, provided efficient fibre-chip coupling can be achieved.

@article{
 title = {Enhanced conductivity along lateral homojunction interfaces of atomically thin semiconductors},
 type = {article},
 year = {2017},
 volume = {4},
 month = {2},
 id = {fac75d3c-8d37-3865-8864-656798255f84},
 created = {2020-12-18T06:00:38.736Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:38.736Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 private_publication = {false},
 bibtype = {article},
 author = {Ying, Jia and Teodor K, Stanev and Erik J, Lenferink and Stern, Nathaniel P},
 journal = {2017 IOP Publishing Ltd},
 number = {2}
}

@article{
 title = {Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5},
 type = {article},
 year = {2016},
 keywords = {Crystal growth,Oxide-fluoride,Piezoelectricity,Triboluminescence},
 pages = {78-82},
 volume = {236},
 websites = {http://www.sciencedirect.com/science/article/pii/S0022459615300621},
 month = {4},
 series = {Materials Discovery Through Crystal Growth},
 id = {249901de-fbce-3508-ab1a-2b17b473a51d},
 created = {2020-12-18T06:00:33.793Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:33.793Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 abstract = {Single crystals of the noncentrosymmetric KNaNbOF5 polymorph were grown for piezoelectric and triboluminescent measurements. Piezoelectric measurements yielded a d33 value of ±6.3 pCN−1 and an effective electromechanical coupling coefficient of up to 0.1565 in the frequency range 1960–2080kHz. Crystals of KNaNbOF5 were found to exhibit a strong triboluminscence effect visible to the naked eye as blue sparks when crystals are crushed. This triboluminescence effect is uncommon in that it is likely independent from both the piezoelectric effect and atmospheric electrical discharge. Instead, triboluminescence may originate from crystal defects or be related to an electroluminescence effect.},
 bibtype = {article},
 author = {Chang, Kelvin B and Edwards, Bryce W and Frazer, Laszlo and Lenferink, Erik J and Stanev, Teodor K and Stern, Nathaniel P and Nino, Juan C and Poeppelmeier, Kenneth R},
 doi = {10.1016/j.jssc.2015.07.011},
 journal = {Journal of Solid State Chemistry}
}

Single crystals of the noncentrosymmetric KNaNbOF5 polymorph were grown for piezoelectric and triboluminescent measurements. Piezoelectric measurements yielded a d33 value of ±6.3 pCN−1 and an effective electromechanical coupling coefficient of up to 0.1565 in the frequency range 1960–2080kHz. Crystals of KNaNbOF5 were found to exhibit a strong triboluminscence effect visible to the naked eye as blue sparks when crystals are crushed. This triboluminescence effect is uncommon in that it is likely independent from both the piezoelectric effect and atmospheric electrical discharge. Instead, triboluminescence may originate from crystal defects or be related to an electroluminescence effect.

@article{
 title = {Silicon-nitride photonic circuits interfaced with monolayer MoS2},
 type = {article},
 year = {2015},
 keywords = {stern:astro},
 pages = {91112},
 volume = {107},
 websites = {https://aip.scitation.org/doi/10.1063/1.4929779},
 month = {8},
 id = {9ab4b395-8a9d-3810-be2c-e69b6876969a},
 created = {2020-12-18T06:00:34.418Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:34.418Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 private_publication = {false},
 bibtype = {article},
 author = {Wei, Guohua and Stanev, Teodor K and Czaplewski, David A and Jung, Il Woong and Stern, Nathaniel P},
 doi = {10.1063/1.4929779},
 journal = {Applied Physics Letters},
 number = {9}
}

@article{
 title = {Evaluation of defects in cuprous oxide through exciton luminescence imaging},
 type = {article},
 year = {2015},
 keywords = {CuO,Cuprous oxide,Excitons,Hyperspectral imaging,Stress,Vacancies},
 pages = {294-302},
 volume = {159},
 websites = {http://www.sciencedirect.com/science/article/pii/S0022231314006851},
 month = {3},
 id = {5819f7ce-322b-3793-898f-1bce59b1c778},
 created = {2020-12-18T06:00:35.174Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:35.174Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {en},
 private_publication = {false},
 abstract = {The various decay mechanisms of excitons in cuprous oxide (Cu2O) are highly sensitive to defects which can relax selection rules. Here we report cryogenic hyperspectral imaging of exciton luminescence from cuprous oxide crystals grown via the floating zone method showing that the samples have few defects. Some locations, however, show strain splitting of the 1s orthoexciton triplet polariton luminescence. Strain is reduced by annealing. In addition, annealing causes annihilation of oxygen and copper vacancies, which leads to a negative correlation between luminescence of unlike vacancies.},
 bibtype = {article},
 author = {Frazer, Laszlo and Lenferink, Erik J and Chang, Kelvin B and Poeppelmeier, Kenneth R and Stern, Nathaniel P and Ketterson, John B},
 doi = {10.1016/j.jlumin.2014.11.035},
 journal = {Journal of Luminescence}
}

The various decay mechanisms of excitons in cuprous oxide (Cu2O) are highly sensitive to defects which can relax selection rules. Here we report cryogenic hyperspectral imaging of exciton luminescence from cuprous oxide crystals grown via the floating zone method showing that the samples have few defects. Some locations, however, show strain splitting of the 1s orthoexciton triplet polariton luminescence. Strain is reduced by annealing. In addition, annealing causes annihilation of oxygen and copper vacancies, which leads to a negative correlation between luminescence of unlike vacancies.

@inproceedings{
 title = {Interfacing Monolayer MoS2 with Silicon-Nitride Integrated Photonics},
 type = {inproceedings},
 year = {2015},
 keywords = {Coupled resonators,Microresonators,Optical devices,Q factor,Ring resonators,Tunable diode lasers},
 pages = {IM4A.3},
 websites = {https://www.osapublishing.org/abstract.cfm?uri=IPRSN-2015-IM4A.3},
 month = {6},
 publisher = {Optical Society of America},
 id = {2196a96d-ce47-30e0-94a3-cb98b51f7401},
 created = {2020-12-18T06:00:37.334Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:37.334Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {inproceedings},
 language = {EN},
 private_publication = {false},
 abstract = {We report integration of monolayer molybdenum disulphide with silicon nitride microresonators assembled by visco-elastic layer transfer techniques. Coupling between the photonic mode and the monolayer semiconductor flakes is confirmed by Q reduction.},
 bibtype = {inproceedings},
 author = {Wei, Guohua and Stanev, Teodor K and Czaplewski, David and Jung, Il Woong and Stern, Nathaniel P},
 doi = {10.1364/IPRSN.2015.IM4A.3},
 booktitle = {Advanced Photonics 2015 (2015), paper IM4A.3}
}

We report integration of monolayer molybdenum disulphide with silicon nitride microresonators assembled by visco-elastic layer transfer techniques. Coupling between the photonic mode and the monolayer semiconductor flakes is confirmed by Q reduction.

@article{
 title = {Coherent optical non-reciprocity in axisymmetric resonators},
 type = {article},
 year = {2014},
 keywords = {Electric fields,Light matter interactions,Light propagation,Light transmission,Mode conversion,Quantum information processing},
 pages = {16099-16111},
 volume = {22},
 websites = {https://www.osapublishing.org/oe/abstract.cfm?uri=oe-22-13-16099},
 month = {6},
 id = {b9d99a03-0158-372f-a8af-1f6d611f068f},
 created = {2020-12-18T06:00:36.006Z},
 file_attached = {false},
 profile_id = {8e06da9e-cb81-3353-9244-a0df0d52905d},
 group_id = {f41a1b35-d892-30f4-b9a4-ee2a344e7432},
 last_modified = {2020-12-18T06:00:36.006Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {false},
 hidden = {false},
 source_type = {article},
 language = {EN},
 private_publication = {false},
 abstract = {We describe an approach to optical non-reciprocity that exploits the local helicity of evanescent electric fields in axisymmetric resonators. By interfacing an optical cavity to helicity-sensitive transitions, such as Zeeman levels in a quantum dot, light transmission through a waveguide becomes direction-dependent when the state degeneracy is lifted. Using a linearized quantum master equation, we analyze the configurations that exhibit non-reciprocity, and we show that reasonable parameters from existing cavity QED experiments are sufficient to demonstrate a coherent non-reciprocal optical isolator operating at the level of a single photon.},
 bibtype = {article},
 author = {Lenferink, Erik J and Wei, Guohua and Stern, Nathaniel P},
 doi = {10.1364/OE.22.016099},
 journal = {Optics Express},
 number = {13}
}

We describe an approach to optical non-reciprocity that exploits the local helicity of evanescent electric fields in axisymmetric resonators. By interfacing an optical cavity to helicity-sensitive transitions, such as Zeeman levels in a quantum dot, light transmission through a waveguide becomes direction-dependent when the state degeneracy is lifted. Using a linearized quantum master equation, we analyze the configurations that exhibit non-reciprocity, and we show that reasonable parameters from existing cavity QED experiments are sufficient to demonstrate a coherent non-reciprocal optical isolator operating at the level of a single photon.