Junyong Wang
Group: Prof Goki Eda
CA2DM Publications:
2024 |
Wang, Zhe; Kalathingal, Vijith; Trushin, Maxim; Liu, Jiawei; Wang, Junyong; Guo, Yongxin; Ozyilmaz, Barbaros; Nijhuis, Christian A; Eda, Goki Upconversion electroluminescence in 2D semiconductors integrated with plasmonic tunnel junctions Journal Article NATURE NANOTECHNOLOGY, 2024, ISSN: 1748-3387. @article{ISI:001205711600001, title = {Upconversion electroluminescence in 2D semiconductors integrated with plasmonic tunnel junctions}, author = {Zhe Wang and Vijith Kalathingal and Maxim Trushin and Jiawei Liu and Junyong Wang and Yongxin Guo and Barbaros Ozyilmaz and Christian A Nijhuis and Goki Eda}, doi = {10.1038/s41565-024-01650-0}, times_cited = {0}, issn = {1748-3387}, year = {2024}, date = {2024-04-19}, journal = {NATURE NANOTECHNOLOGY}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Plasmonic tunnel junctions are a unique electroluminescent system in which light emission occurs via an interplay between tunnelling electrons and plasmonic fields instead of electron-hole recombination as in conventional light-emitting diodes. It was previously shown that placing luminescent molecules in the tunneling pathway of nanoscopic tunnel junctions results in peculiar upconversion electroluminescence where the energy of emitted photons exceeds that of excitation electrons. Here we report the observation of upconversion electroluminescence in macroscopic van der Waals plasmonic tunnel junctions comprising gold and few-layer graphene electrodes separated by a similar to 2-nm-thick hexagonal boron nitride tunnel barrier and a monolayer semiconductor. We find that the semiconductor ground exciton emission is triggered at excitation electron energies lower than the semiconductor optical gap. Interestingly, this upconversion is reached in devices operating at a low conductance (<10(-6) S) and low power density regime (<10(2) W cm(-2)), defying explanation through existing proposed mechanisms. By examining the scaling relationship between plasmonic and excitonic emission intensities, we elucidate the role of inelastic electron tunnelling dipoles that induce optically forbidden transitions in the few-layer graphene electrode and ultrafast hot carrier transfer across the van der Waals interface.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Plasmonic tunnel junctions are a unique electroluminescent system in which light emission occurs via an interplay between tunnelling electrons and plasmonic fields instead of electron-hole recombination as in conventional light-emitting diodes. It was previously shown that placing luminescent molecules in the tunneling pathway of nanoscopic tunnel junctions results in peculiar upconversion electroluminescence where the energy of emitted photons exceeds that of excitation electrons. Here we report the observation of upconversion electroluminescence in macroscopic van der Waals plasmonic tunnel junctions comprising gold and few-layer graphene electrodes separated by a similar to 2-nm-thick hexagonal boron nitride tunnel barrier and a monolayer semiconductor. We find that the semiconductor ground exciton emission is triggered at excitation electron energies lower than the semiconductor optical gap. Interestingly, this upconversion is reached in devices operating at a low conductance (<10(-6) S) and low power density regime (<10(2) W cm(-2)), defying explanation through existing proposed mechanisms. By examining the scaling relationship between plasmonic and excitonic emission intensities, we elucidate the role of inelastic electron tunnelling dipoles that induce optically forbidden transitions in the few-layer graphene electrode and ultrafast hot carrier transfer across the van der Waals interface. |
2023 |
Ren, Tianhua; Wang, Junyong; Han, Kaizhen; Kang, Yuye; Kumar, Annie; Zhang, Gong; Wang, Zhe; Oulton, Rupert F; Eda, Goki; Gong, Xiao Optical Gain Spectrum and Confinement Factor of a Monolayer Semiconductor in an Ultrahigh-Quality Cavity Journal Article NANO LETTERS, 23 (24), pp. 11601-11607, 2023, ISSN: 1530-6984. @article{ISI:001133459300001, title = {Optical Gain Spectrum and Confinement Factor of a Monolayer Semiconductor in an Ultrahigh-Quality Cavity}, author = {Tianhua Ren and Junyong Wang and Kaizhen Han and Yuye Kang and Annie Kumar and Gong Zhang and Zhe Wang and Rupert F Oulton and Goki Eda and Xiao Gong}, doi = {10.1021/acs.nanolett.3c03357}, times_cited = {0}, issn = {1530-6984}, year = {2023}, date = {2023-12-08}, journal = {NANO LETTERS}, volume = {23}, number = {24}, pages = {11601-11607}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Two-dimensional (2D) semiconductors have attracted great attention as a novel class of gain materials for low-threshold, on-chip coherent light sources. Despite several experimental reports on lasing, the underlying gain mechanism of 2D materials remains elusive due to a lack of key information, including modal gain and the confinement factor. Here, we demonstrate a novel approach to directly determine the absorption coefficient of monolayer WS2 by characterizing the whispering gallery modes in a van der Waals microdisk cavity. By exploiting the cavity's high intrinsic quality factor of 2.5 x 10(4), the absorption coefficient spectrum and confinement factor are experimentally resolved with unprecedented accuracy. The excitonic gain reduces the WS2 absorption coefficient by 2 x 10(4) cm(-1) at room temperature, and the experimental confinement factor is found to agree with the theoretical prediction. These results are essential for unveiling the gain mechanism in emergent, low-threshold 2D-semiconductor-based laser devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) semiconductors have attracted great attention as a novel class of gain materials for low-threshold, on-chip coherent light sources. Despite several experimental reports on lasing, the underlying gain mechanism of 2D materials remains elusive due to a lack of key information, including modal gain and the confinement factor. Here, we demonstrate a novel approach to directly determine the absorption coefficient of monolayer WS2 by characterizing the whispering gallery modes in a van der Waals microdisk cavity. By exploiting the cavity's high intrinsic quality factor of 2.5 x 10(4), the absorption coefficient spectrum and confinement factor are experimentally resolved with unprecedented accuracy. The excitonic gain reduces the WS2 absorption coefficient by 2 x 10(4) cm(-1) at room temperature, and the experimental confinement factor is found to agree with the theoretical prediction. These results are essential for unveiling the gain mechanism in emergent, low-threshold 2D-semiconductor-based laser devices. |
Guo, Qiangbing; Qi, Xiao-Zhuo; Zhang, Lishu; Gao, Meng; Hu, Sanlue; Zhou, Wenju; Zang, Wenjie; Zhao, Xiaoxu; Wang, Junyong; Yan, Bingmin; Xu, Mingquan; Wu, Yun-Kun; Eda, Goki; Xiao, Zewen; Yang, Shengyuan A; Gou, Huiyang; Feng, Yuan Ping; Guo, Guang-Can; Zhou, Wu; Ren, Xi-Feng; Qiu, Cheng-Wei; Pennycook, Stephen J; Wee, Andrew T S Ultrathin quantum light source with van der Waals NbOCl2 crystal Journal Article NATURE, 613 (7942), pp. 53-+, 2023, ISSN: 0028-0836. @article{ISI:000955711300008, title = {Ultrathin quantum light source with van der Waals NbOCl_{2} crystal}, author = {Qiangbing Guo and Xiao-Zhuo Qi and Lishu Zhang and Meng Gao and Sanlue Hu and Wenju Zhou and Wenjie Zang and Xiaoxu Zhao and Junyong Wang and Bingmin Yan and Mingquan Xu and Yun-Kun Wu and Goki Eda and Zewen Xiao and Shengyuan A Yang and Huiyang Gou and Yuan Ping Feng and Guang-Can Guo and Wu Zhou and Xi-Feng Ren and Cheng-Wei Qiu and Stephen J Pennycook and Andrew T S Wee}, doi = {10.1038/s41586-022-05393-7}, times_cited = {9}, issn = {0028-0836}, year = {2023}, date = {2023-01-05}, journal = {NATURE}, volume = {613}, number = {7942}, pages = {53-+}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Interlayer electronic coupling in two-dimensional materials enables tunable and emergent properties by stacking engineering. However, it also results in significant evolution of electronic structures and attenuation of excitonic effects in two-dimensional semiconductors as exemplified by quickly degrading excitonic photoluminescence and optical nonlinearities in transition metal dichalcogenides when monolayers are stacked into van der Waals structures. Here we report a van der Waals crystal, niobium oxide dichloride (NbOCl2), featuring vanishing interlayer electronic coupling and monolayer-like excitonic behaviour in the bulk form, along with a scalable second-harmonic generation intensity of up to three orders higher than that in monolayer WS2. Notably, the strong second-order nonlinearity enables correlated parametric photon pair generation, through a spontaneous parametric down-conversion (SPDC) process, in flakes as thin as about 46 nm. To our knowledge, this is the first SPDC source unambiguously demonstrated in two-dimensional layered materials, and the thinnest SPDC source ever reported. Our work opens an avenue towards developing van der Waals material-based ultracompact on-chip SPDC sources as well as high-performance photon modulators in both classical and quantum optical technologies(1-4).}, keywords = {}, pubstate = {published}, tppubtype = {article} } Interlayer electronic coupling in two-dimensional materials enables tunable and emergent properties by stacking engineering. However, it also results in significant evolution of electronic structures and attenuation of excitonic effects in two-dimensional semiconductors as exemplified by quickly degrading excitonic photoluminescence and optical nonlinearities in transition metal dichalcogenides when monolayers are stacked into van der Waals structures. Here we report a van der Waals crystal, niobium oxide dichloride (NbOCl2), featuring vanishing interlayer electronic coupling and monolayer-like excitonic behaviour in the bulk form, along with a scalable second-harmonic generation intensity of up to three orders higher than that in monolayer WS2. Notably, the strong second-order nonlinearity enables correlated parametric photon pair generation, through a spontaneous parametric down-conversion (SPDC) process, in flakes as thin as about 46 nm. To our knowledge, this is the first SPDC source unambiguously demonstrated in two-dimensional layered materials, and the thinnest SPDC source ever reported. Our work opens an avenue towards developing van der Waals material-based ultracompact on-chip SPDC sources as well as high-performance photon modulators in both classical and quantum optical technologies(1-4). |
2021 |
Shi, Shuyuan; Li, Jie; Hsu, Chuang-Han; Lee, Kyusup; Wang, Yi; Yang, Li; Wang, Junyong; Wang, Qisheng; Wu, Hao; Zhang, Wenfeng; Eda, Goki; Liang, Gengchiau; Chang, Haixin; Yang, Hyunsoo Observation of the Out-of-Plane Polarized Spin Current from CVD Grown WTe2 Journal Article ADVANCED QUANTUM TECHNOLOGIES, 4 (8), 2021. @article{ISI:000663272500001, title = {Observation of the Out-of-Plane Polarized Spin Current from CVD Grown WTe_{2}}, author = {Shuyuan Shi and Jie Li and Chuang-Han Hsu and Kyusup Lee and Yi Wang and Li Yang and Junyong Wang and Qisheng Wang and Hao Wu and Wenfeng Zhang and Goki Eda and Gengchiau Liang and Haixin Chang and Hyunsoo Yang}, doi = {10.1002/qute.202100038}, times_cited = {0}, year = {2021}, date = {2021-06-19}, journal = {ADVANCED QUANTUM TECHNOLOGIES}, volume = {4}, number = {8}, publisher = {WILEY}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {Weyl semimetal Td-phase WTe2 possesses the spin-resolved band structure with strong spin-orbit coupling, holding promises as a useful spin source material. The noncentrosymmetric crystalline structure of Td-WTe2 endows the generation of the out-of-plane polarized spin, which is of great interest in magnetic memory applications. Previously, WTe2 was explored in spin devices based on mechanically exfoliated single crystal flakes with a size of micrometers. For practical spintronics applications, it is highly desirable to implement wafer-scale thin films. In this work, centimeter-scale chemical vapor deposition (CVD) grown Td-WTe2 thin films are used and the spin current generation is studied by the spin torque ferromagnetic resonance (ST-FMR) technique. The in-plane and out-of-plane spin conductivities of 7.36 x 10(3) (PLANCK CONSTANT OVER TWO PI/2e) (ohm m)(-1) and 1.76 x 10(3) (PLANCK CONSTANT OVER TWO PI/2e) (ohm m)(-1), respectively, are found in CVD-growth 5 nm-WTe2. The current-induced magnetization switching in WTe2/NiFe is demonstrated at room temperature in the domain wall motion regime, which may invigorate potential spintronic device innovations based on Weyl semimetals.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Weyl semimetal Td-phase WTe2 possesses the spin-resolved band structure with strong spin-orbit coupling, holding promises as a useful spin source material. The noncentrosymmetric crystalline structure of Td-WTe2 endows the generation of the out-of-plane polarized spin, which is of great interest in magnetic memory applications. Previously, WTe2 was explored in spin devices based on mechanically exfoliated single crystal flakes with a size of micrometers. For practical spintronics applications, it is highly desirable to implement wafer-scale thin films. In this work, centimeter-scale chemical vapor deposition (CVD) grown Td-WTe2 thin films are used and the spin current generation is studied by the spin torque ferromagnetic resonance (ST-FMR) technique. The in-plane and out-of-plane spin conductivities of 7.36 x 10(3) (PLANCK CONSTANT OVER TWO PI/2e) (ohm m)(-1) and 1.76 x 10(3) (PLANCK CONSTANT OVER TWO PI/2e) (ohm m)(-1), respectively, are found in CVD-growth 5 nm-WTe2. The current-induced magnetization switching in WTe2/NiFe is demonstrated at room temperature in the domain wall motion regime, which may invigorate potential spintronic device innovations based on Weyl semimetals. |
Loh, Leyi; Chen, Yifeng; Wang, Junyong; Yin, Xinmao; Tang, Chi Sin; Zhang, Qi; Watanabe, Kenji; Taniguchi, Takashi; Wee, Andrew T S; Bosman, Michel; Quek, Su Ying; Eda, Goki Impurity-Induced Emission in Re-Doped WS2 Monolayers Journal Article NANO LETTERS, 21 (12), pp. 5293-5300, 2021, ISSN: 1530-6984. @article{ISI:000668003400052, title = {Impurity-Induced Emission in Re-Doped WS_{2} Monolayers}, author = {Leyi Loh and Yifeng Chen and Junyong Wang and Xinmao Yin and Chi Sin Tang and Qi Zhang and Kenji Watanabe and Takashi Taniguchi and Andrew T S Wee and Michel Bosman and Su Ying Quek and Goki Eda}, doi = {10.1021/acs.nanolett.1c01439}, times_cited = {0}, issn = {1530-6984}, year = {2021}, date = {2021-06-11}, journal = {NANO LETTERS}, volume = {21}, number = {12}, pages = {5293-5300}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Impurity doping is a viable route toward achieving desired subgap optical response in semiconductors. In strongly excitonic two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDs), impurities are expected to result in bound-exciton emission. However, doped TMDs often exhibit a broad Stokes-shifted emission without characteristic features, hampering strategic materials engineering. Here we report observation of a well-defined impurity-induced emission in monolayer WS2 substitutionally doped with rhenium (Re), which is an electron donor. The emission exhibits characteristics of localized states and dominates the spectrum up to 200 K. Gate dependence reveals that neutral impurity centers are responsible for the observed emission. Using GW-Bethe-Salpeter equation (GW-BSE) calculations, we attribute the emission to transitions between spin-split upper Re band and valence band edge.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Impurity doping is a viable route toward achieving desired subgap optical response in semiconductors. In strongly excitonic two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDs), impurities are expected to result in bound-exciton emission. However, doped TMDs often exhibit a broad Stokes-shifted emission without characteristic features, hampering strategic materials engineering. Here we report observation of a well-defined impurity-induced emission in monolayer WS2 substitutionally doped with rhenium (Re), which is an electron donor. The emission exhibits characteristics of localized states and dominates the spectrum up to 200 K. Gate dependence reveals that neutral impurity centers are responsible for the observed emission. Using GW-Bethe-Salpeter equation (GW-BSE) calculations, we attribute the emission to transitions between spin-split upper Re band and valence band edge. |
Li, Jiahan; Wang, Junyong; Zhang, Xiaotian; Elias, Christine; Ye, Gaihua; Evans, Dylan; Eda, Goki; Redwing, Joan M; Cassabois, Guillaume; Gil, Bernard; Valvin, Pierre; He, Rui; Liu, Bin; Edgar, James H Hexagonal Boron Nitride Crystal Growth from Iron, a Single Component Flux Journal Article ACS NANO, 15 (4), pp. 7032-7039, 2021, ISSN: 1936-0851. @article{ISI:000645436800093, title = {Hexagonal Boron Nitride Crystal Growth from Iron, a Single Component Flux}, author = {Jiahan Li and Junyong Wang and Xiaotian Zhang and Christine Elias and Gaihua Ye and Dylan Evans and Goki Eda and Joan M Redwing and Guillaume Cassabois and Bernard Gil and Pierre Valvin and Rui He and Bin Liu and James H Edgar}, doi = {10.1021/acsnano.1c00115}, times_cited = {0}, issn = {1936-0851}, year = {2021}, date = {2021-04-05}, journal = {ACS NANO}, volume = {15}, number = {4}, pages = {7032-7039}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The highest quality hexagonal boron nitride (hBN) crystals are grown from molten solutions. For hBN crystal growth at atmospheric pressure, typically the solvent is a combination of two metals, one with a high boron solubility and the other to promote nitrogen solubility. In this study, we demonstrate that high-quality hBN crystals can be grown at atmospheric pressure using pure iron as a flux. The ability to produce excellent-quality hBN crystals using pure iron as a solvent is unexpected, given its low solubility for nitrogen. The properties of crystals produced with this flux matched the best values ever reported for hBN: a narrow Raman E-2g vibration peak (7.6 cm(-1)) and strong phonon-assisted peaks in the photoluminescence spectra. To further test their quality, the hBN crytals were used as a substrate for WSe2 epitaxy. WSe2 was deposited with a low nucleation density, indicating the low defect density of the hBN. Lastly, the carrier tunneling through our hBN thin layers (3.5 nm) follows the Fowler-Nordheim model, with a barrier height of 3.7 eV, demonstrating hBN's superior electrical insulating properties. This ability to produce high-quality hBN crystals in such a simple, environmentally friendly and economical process will advance two-dimensional material research by enabling integrated devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The highest quality hexagonal boron nitride (hBN) crystals are grown from molten solutions. For hBN crystal growth at atmospheric pressure, typically the solvent is a combination of two metals, one with a high boron solubility and the other to promote nitrogen solubility. In this study, we demonstrate that high-quality hBN crystals can be grown at atmospheric pressure using pure iron as a flux. The ability to produce excellent-quality hBN crystals using pure iron as a solvent is unexpected, given its low solubility for nitrogen. The properties of crystals produced with this flux matched the best values ever reported for hBN: a narrow Raman E-2g vibration peak (7.6 cm(-1)) and strong phonon-assisted peaks in the photoluminescence spectra. To further test their quality, the hBN crytals were used as a substrate for WSe2 epitaxy. WSe2 was deposited with a low nucleation density, indicating the low defect density of the hBN. Lastly, the carrier tunneling through our hBN thin layers (3.5 nm) follows the Fowler-Nordheim model, with a barrier height of 3.7 eV, demonstrating hBN's superior electrical insulating properties. This ability to produce high-quality hBN crystals in such a simple, environmentally friendly and economical process will advance two-dimensional material research by enabling integrated devices. |
Kumar, Dushyant; Hsu, Chuang-Han; Sharma, Raghav; Chang, Tay-Rong; Yu, Peng; Wang, Junyong; Eda, Goki; Liang, Gengchiau; Yang, Hyunsoo Room-temperature nonlinear Hall effect and wireless radiofrequency rectification in Weyl semimetal TaIrTe4 Journal Article NATURE NANOTECHNOLOGY, 16 (4), pp. 421-+, 2021, ISSN: 1748-3387. @article{ISI:000611456700002, title = {Room-temperature nonlinear Hall effect and wireless radiofrequency rectification in Weyl semimetal TaIrTe_{4}}, author = {Dushyant Kumar and Chuang-Han Hsu and Raghav Sharma and Tay-Rong Chang and Peng Yu and Junyong Wang and Goki Eda and Gengchiau Liang and Hyunsoo Yang}, doi = {10.1038/s41565-020-00839-3}, times_cited = {0}, issn = {1748-3387}, year = {2021}, date = {2021-01-25}, journal = {NATURE NANOTECHNOLOGY}, volume = {16}, number = {4}, pages = {421-+}, publisher = {NATURE RESEARCH}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {The nonlinear Hall effect (NLHE), the phenomenon in which a transverse voltage can be produced without a magnetic field, provides a potential alternative for rectification or frequency doubling(1,2). However, the low-temperature detection of the NLHE limits its applications(3,4). Here, we report the room-temperature NLHE in a type-II Weyl semimetal TaIrTe4, which hosts a robust NLHE due to broken inversion symmetry and large band overlapping at the Fermi level. We also observe a temperature-induced sign inversion of the NLHE in TaIrTe4. Our theoretical calculations suggest that the observed sign inversion is a result of a temperature-induced shift in the chemical potential, indicating a direct correlation of the NLHE with the electronic structure at the Fermi surface. Finally, on the basis of the observed room-temperature NLHE in TaIrTe4 we demonstrate the wireless radiofrequency (RF) rectification with zero external bias and magnetic field. This work opens a door to realizing room-temperature applications based on the NLHE in Weyl semimetals.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The nonlinear Hall effect (NLHE), the phenomenon in which a transverse voltage can be produced without a magnetic field, provides a potential alternative for rectification or frequency doubling(1,2). However, the low-temperature detection of the NLHE limits its applications(3,4). Here, we report the room-temperature NLHE in a type-II Weyl semimetal TaIrTe4, which hosts a robust NLHE due to broken inversion symmetry and large band overlapping at the Fermi level. We also observe a temperature-induced sign inversion of the NLHE in TaIrTe4. Our theoretical calculations suggest that the observed sign inversion is a result of a temperature-induced shift in the chemical potential, indicating a direct correlation of the NLHE with the electronic structure at the Fermi surface. Finally, on the basis of the observed room-temperature NLHE in TaIrTe4 we demonstrate the wireless radiofrequency (RF) rectification with zero external bias and magnetic field. This work opens a door to realizing room-temperature applications based on the NLHE in Weyl semimetals. |
2020 |
Wang, Qixing; Zhang, Qi; Luo, Xin; Wang, Junyong; Zhu, Rui; Liang, Qijie; Zhang, Lei; Yong, Justin Zhou; Wong, Calvin Pei Yu; Eda, Goki; Smet, Jurgen H; Wee, Andrew T S Optoelectronic Properties of a van der Waals WS2 Monolayer/2D Perovskite Vertical Heterostructure Journal Article ACS APPLIED MATERIALS & INTERFACES, 12 (40), pp. 45235-45242, 2020, ISSN: 1944-8244. @article{ISI:000579956100085, title = {Optoelectronic Properties of a van der Waals WS_{2} Monolayer/2D Perovskite Vertical Heterostructure}, author = {Qixing Wang and Qi Zhang and Xin Luo and Junyong Wang and Rui Zhu and Qijie Liang and Lei Zhang and Justin Zhou Yong and Calvin Pei Yu Wong and Goki Eda and Jurgen H Smet and Andrew T S Wee}, doi = {10.1021/acsami.0c14398}, times_cited = {0}, issn = {1944-8244}, year = {2020}, date = {2020-10-07}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {12}, number = {40}, pages = {45235-45242}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Two-dimensional (2D) Ruddlesden-Popper perovskites have been demonstrated to possess great potential for optical and optoelectronic devices. Because they exhibit better ambient stability than three-dimensional (3D) perovskites, they have been considered as potential substitutes for 3D perovskites as light absorbing layers to improve the photoresponsivity of monolayer transition metal dichalcogenide (TMDC)-based photodetectors. Investigation of the optoelectronic properties of TMDC monolayer/2D perovskite vertical heterostructures is however at an early stage. Here, we address the photovoltaic effect and the photodetection performance in tungsten disulfide (WS2) monolayer/2D perovskite (C6H5C2H4NH3)(2)PbI4 (PEPI) vertical heterostructures. A vertical device geometry with separate graphene contacts to both heterointerface constituents acted as a photovoltaic device and self-driven photodetector. The photovoltaic device exhibited an open circuit voltage of-0.57 V and a short circuit current of 41.6 nA. A photoresponsivity of 0.13 mA/W at the WS2/PEPI heterointerface was achieved, which was signified by a factor of 5 compared to that from the individual WS2 region. The current on/off ratio of the self-driven photodetector was approximately 1500. The photoresponsivity and external quantum efficiency of the self-driven photodetector were estimated to be 24.2 mu A/W and 5.7 x 10(5), respectively. This work corroborates that 2D perovskites are promising light absorbing layers in optoelectronic devices with a TMDC-based heterointerface.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) Ruddlesden-Popper perovskites have been demonstrated to possess great potential for optical and optoelectronic devices. Because they exhibit better ambient stability than three-dimensional (3D) perovskites, they have been considered as potential substitutes for 3D perovskites as light absorbing layers to improve the photoresponsivity of monolayer transition metal dichalcogenide (TMDC)-based photodetectors. Investigation of the optoelectronic properties of TMDC monolayer/2D perovskite vertical heterostructures is however at an early stage. Here, we address the photovoltaic effect and the photodetection performance in tungsten disulfide (WS2) monolayer/2D perovskite (C6H5C2H4NH3)(2)PbI4 (PEPI) vertical heterostructures. A vertical device geometry with separate graphene contacts to both heterointerface constituents acted as a photovoltaic device and self-driven photodetector. The photovoltaic device exhibited an open circuit voltage of-0.57 V and a short circuit current of 41.6 nA. A photoresponsivity of 0.13 mA/W at the WS2/PEPI heterointerface was achieved, which was signified by a factor of 5 compared to that from the individual WS2 region. The current on/off ratio of the self-driven photodetector was approximately 1500. The photoresponsivity and external quantum efficiency of the self-driven photodetector were estimated to be 24.2 mu A/W and 5.7 x 10(5), respectively. This work corroborates that 2D perovskites are promising light absorbing layers in optoelectronic devices with a TMDC-based heterointerface. |
Wang, Junyong; Zhou, Yong Justin; Xiang, Du; Ng, Shiuan Jun; Watanabe, Kenji; Taniguchi, Takashi; Eda, Goki Polarized Light-Emitting Diodes Based on Anisotropic Excitons in Few-Layer ReS2 Journal Article ADVANCED MATERIALS, 32 (32), 2020, ISSN: 0935-9648. @article{ISI:000544184000001, title = {Polarized Light-Emitting Diodes Based on Anisotropic Excitons in Few-Layer ReS_{2}}, author = {Junyong Wang and Yong Justin Zhou and Du Xiang and Shiuan Jun Ng and Kenji Watanabe and Takashi Taniguchi and Goki Eda}, doi = {10.1002/adma.202001890}, times_cited = {0}, issn = {0935-9648}, year = {2020}, date = {2020-06-30}, journal = {ADVANCED MATERIALS}, volume = {32}, number = {32}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {An on-chip polarized light source is desirable in signal processing, optical communication, and display applications. Layered semiconductors with reduced in-plane symmetry have inherent anisotropic excitons that are attractive candidates as polarized dipole emitters. Herein, the demonstration of polarized light-emitting diode based on anisotropic excitons in few-layer ReS2, a 2D semiconductor with excitonic transition energy of 1.5-1.6 eV, is reported. The light-emitting device is based on minority carrier (hole) injection into n-type ReS(2)through a hexagonal boron nitride (hBN) tunnel barrier in a metal-insulator-semiconductor (MIS) van der Waals heterostack. Two distinct emission peaks from excitons are observed at near-infrared wavelength regime from few-layer ReS2. The emissions exhibit a degree of polarization of 80% reflecting the nearly 1D nature of excitons in ReS2.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An on-chip polarized light source is desirable in signal processing, optical communication, and display applications. Layered semiconductors with reduced in-plane symmetry have inherent anisotropic excitons that are attractive candidates as polarized dipole emitters. Herein, the demonstration of polarized light-emitting diode based on anisotropic excitons in few-layer ReS2, a 2D semiconductor with excitonic transition energy of 1.5-1.6 eV, is reported. The light-emitting device is based on minority carrier (hole) injection into n-type ReS(2)through a hexagonal boron nitride (hBN) tunnel barrier in a metal-insulator-semiconductor (MIS) van der Waals heterostack. Two distinct emission peaks from excitons are observed at near-infrared wavelength regime from few-layer ReS2. The emissions exhibit a degree of polarization of 80% reflecting the nearly 1D nature of excitons in ReS2. |
Li, Jiahan; Yuan, Chao; Elias, Christine; Wang, Junyong; Zhang, Xiaotian; Ye, Gaihua; Huang, Chaoran; Kuball, Martin; Eda, Goki; Redwing, Joan M; He, Rui; Cassabois, Guillaume; Gil, Bernard; Valvin, Pierre; Pelini, Thomas; Liu, Bin; Edgar, James H Hexagonal Boron Nitride Single Crystal Growth from Solution with a Temperature Gradient Journal Article CHEMISTRY OF MATERIALS, 32 (12), pp. 5066-5072, 2020, ISSN: 0897-4756. @article{ISI:000543738500018, title = {Hexagonal Boron Nitride Single Crystal Growth from Solution with a Temperature Gradient}, author = {Jiahan Li and Chao Yuan and Christine Elias and Junyong Wang and Xiaotian Zhang and Gaihua Ye and Chaoran Huang and Martin Kuball and Goki Eda and Joan M Redwing and Rui He and Guillaume Cassabois and Bernard Gil and Pierre Valvin and Thomas Pelini and Bin Liu and James H Edgar}, doi = {10.1021/acs.chemmater.0c00830}, times_cited = {0}, issn = {0897-4756}, year = {2020}, date = {2020-06-23}, journal = {CHEMISTRY OF MATERIALS}, volume = {32}, number = {12}, pages = {5066-5072}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Hexagonal boron nitride (hBN) is attracting much attention due to its tremendous applications including nano-photonic and electronic devices, substrates for two-dimensional (2D) materials, heat management materials, etc. To achieve the best device performance, large area hBN single crystals are required. Herein, large-area (>500 mu m each), high-quality (defect density < 0.52/mu m(2)) bulk hBN single crystals are grown from molten metal solutions with a temperature gradient. The narrow Raman line widths of the intralayer E-2g mode peak and the interlayer shear mode, the strong and sharp phonon-assisted transition photoluminescence peaks, and the high thermal conductivity demonstrate that the hBN produced by this method has a high crystal quality with a low density of defects. Atomic force microscope images show that atomically flat layers of hBN can be produced by exfoliation. This study not only demonstrates a new strategy for growing large hBN single crystals but also provides high quality thick and thin hBN layers for nanodevice applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Hexagonal boron nitride (hBN) is attracting much attention due to its tremendous applications including nano-photonic and electronic devices, substrates for two-dimensional (2D) materials, heat management materials, etc. To achieve the best device performance, large area hBN single crystals are required. Herein, large-area (>500 mu m each), high-quality (defect density < 0.52/mu m(2)) bulk hBN single crystals are grown from molten metal solutions with a temperature gradient. The narrow Raman line widths of the intralayer E-2g mode peak and the interlayer shear mode, the strong and sharp phonon-assisted transition photoluminescence peaks, and the high thermal conductivity demonstrate that the hBN produced by this method has a high crystal quality with a low density of defects. Atomic force microscope images show that atomically flat layers of hBN can be produced by exfoliation. This study not only demonstrates a new strategy for growing large hBN single crystals but also provides high quality thick and thin hBN layers for nanodevice applications. |
Yu, Wei; Wang, Zishen; Zhao, Xiaoxu; Wang, Junyong; Herng, Tun Seng; Ma, Teng; Zhu, Zhiyu; Ding, Jun; Eda, Goki; Pennycook, Stephen J; Feng, Yuan Ping; Loh, Kian Ping Domain Engineering in ReS2by Coupling Strain during Electrochemical Exfoliation Journal Article ADVANCED FUNCTIONAL MATERIALS, 30 (31), 2020, ISSN: 1616-301X. @article{ISI:000539579600001, title = {Domain Engineering in ReS_{2}by Coupling Strain during Electrochemical Exfoliation}, author = {Wei Yu and Zishen Wang and Xiaoxu Zhao and Junyong Wang and Tun Seng Herng and Teng Ma and Zhiyu Zhu and Jun Ding and Goki Eda and Stephen J Pennycook and Yuan Ping Feng and Kian Ping Loh}, doi = {10.1002/adfm.202003057}, times_cited = {0}, issn = {1616-301X}, year = {2020}, date = {2020-06-11}, journal = {ADVANCED FUNCTIONAL MATERIALS}, volume = {30}, number = {31}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Chemical exfoliation has been used for the fast and large-scale production of 2D nanosheets from graphene and transition metal dichalcogenides; however, it is rarely used for domain engineering of exfoliated nanosheets. Herein, it is found that the use of large sized molecular intercalants during electrochemical intercalation induce atomic row dislocation and parallel mirror twin boundaries (MTBs) on an otherwise pristine rhenium disulfide (ReS2) crystal, such that the exfoliated flakes possess a parallel, multi-domain structure. These domains can be distinguished under a polarized microscope owing to the intrinsic in-plane optical dichroic properties of ReS2, thereby affording a way to track the number of domains introduced versus the size of the molecular intercalant during electrochemical exfoliation. Ferromagnetism is detected on the intercalated sample using large sized molecular intercalants. Density function theory suggests that these may be due to the coupled effects of lattice strain and S vacancies in the MTBs.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Chemical exfoliation has been used for the fast and large-scale production of 2D nanosheets from graphene and transition metal dichalcogenides; however, it is rarely used for domain engineering of exfoliated nanosheets. Herein, it is found that the use of large sized molecular intercalants during electrochemical intercalation induce atomic row dislocation and parallel mirror twin boundaries (MTBs) on an otherwise pristine rhenium disulfide (ReS2) crystal, such that the exfoliated flakes possess a parallel, multi-domain structure. These domains can be distinguished under a polarized microscope owing to the intrinsic in-plane optical dichroic properties of ReS2, thereby affording a way to track the number of domains introduced versus the size of the molecular intercalant during electrochemical exfoliation. Ferromagnetism is detected on the intercalated sample using large sized molecular intercalants. Density function theory suggests that these may be due to the coupled effects of lattice strain and S vacancies in the MTBs. |
2019 |
Xiang, Du; Liu, Tao; Wang, Junyong; Wang, Peng; Wang, Lin; Zheng, Yue; Wang, Yanan; Gao, Jing; Ang, Kah-Wee; Eda, Goki; Hu, Weida; Liu, Lei; Chen, Wei Anomalous Broadband Spectrum Photodetection in 2D Rhenium Disulfide Transistor Journal Article ADVANCED OPTICAL MATERIALS, 7 (23), 2019, ISSN: 2195-1071. @article{ISI:000501216800004, title = {Anomalous Broadband Spectrum Photodetection in 2D Rhenium Disulfide Transistor}, author = {Du Xiang and Tao Liu and Junyong Wang and Peng Wang and Lin Wang and Yue Zheng and Yanan Wang and Jing Gao and Kah-Wee Ang and Goki Eda and Weida Hu and Lei Liu and Wei Chen}, doi = {10.1002/adom.201901115}, times_cited = {0}, issn = {2195-1071}, year = {2019}, date = {2019-12-01}, journal = {ADVANCED OPTICAL MATERIALS}, volume = {7}, number = {23}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {2D transition metal dichalcogenide (TMD)-based phototransistors generally work under photoconductive, photovoltaic, or photogating mode, in which photocarriers are generated from band-to-band excitation. Nevertheless, due to the relatively large bandgap, most TMD phototransistors working under these modes are restricted in visible spectrum. Here, photodetection in 2D multilayer rhenium disulfide (ReS2) transistor via bolometric mode, which relies on light heating induced conductance change instead of band-to-band photoexcitation is reported, making it possible for sub-bandgap photon detection. The bolometric effect induced photoresponse is first revealed by an anomalous sign switching of photocurrent from positive to negative while increasing gate voltage under visible light, which is further validated by the temperature dependent electrical transport measurements. The phototransistor exhibits remarkable photoresponse under infrared regime, beyond the optical bandgap absorption edge of the ReS2 flake. Additionally, it demonstrates a low noise equivalent power, less than 5 x 10(-2) pW Hz(-1/2), which is very promising for ultra-weak light detection. Moreover, the response time is below 3 ms, nearly 3-4 orders of magnitude faster than previously reported ReS2 photodetectors. The findings promise bolometric effect as an effective photodetection mode to extend the response spectrum of large bandgap TMDs for novel and high-performance broadband photodetectors.}, keywords = {}, pubstate = {published}, tppubtype = {article} } 2D transition metal dichalcogenide (TMD)-based phototransistors generally work under photoconductive, photovoltaic, or photogating mode, in which photocarriers are generated from band-to-band excitation. Nevertheless, due to the relatively large bandgap, most TMD phototransistors working under these modes are restricted in visible spectrum. Here, photodetection in 2D multilayer rhenium disulfide (ReS2) transistor via bolometric mode, which relies on light heating induced conductance change instead of band-to-band photoexcitation is reported, making it possible for sub-bandgap photon detection. The bolometric effect induced photoresponse is first revealed by an anomalous sign switching of photocurrent from positive to negative while increasing gate voltage under visible light, which is further validated by the temperature dependent electrical transport measurements. The phototransistor exhibits remarkable photoresponse under infrared regime, beyond the optical bandgap absorption edge of the ReS2 flake. Additionally, it demonstrates a low noise equivalent power, less than 5 x 10(-2) pW Hz(-1/2), which is very promising for ultra-weak light detection. Moreover, the response time is below 3 ms, nearly 3-4 orders of magnitude faster than previously reported ReS2 photodetectors. The findings promise bolometric effect as an effective photodetection mode to extend the response spectrum of large bandgap TMDs for novel and high-performance broadband photodetectors. |
Wang, Junyong; Lin, Fanrong; Verzhbitskiy, Ivan; Watanabe, Kenji; Taniguchi, Takashi; Martin, Jens; Eda, Gold Polarity Tunable Trionic Electroluminescence in Monolayer WSe2 Journal Article NANO LETTERS, 19 (10), pp. 7470-7475, 2019, ISSN: 1530-6984. @article{ISI:000490353500097, title = {Polarity Tunable Trionic Electroluminescence in Monolayer WSe_{2}}, author = {Junyong Wang and Fanrong Lin and Ivan Verzhbitskiy and Kenji Watanabe and Takashi Taniguchi and Jens Martin and Gold Eda}, doi = {10.1021/acs.nanolett.9b03215}, times_cited = {0}, issn = {1530-6984}, year = {2019}, date = {2019-10-01}, journal = {NANO LETTERS}, volume = {19}, number = {10}, pages = {7470-7475}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Monolayer WSe2 exhibits luminescence arising from various types of exciton complexes due to strong many-body effects. Here, we demonstrate selective electrical excitation of positive and negative trions in van der Waals metal-insulator-semiconductor (MIS) heterostructure consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer WSe2. Intentional unbalanced injection of electrons and holes is achieved via field-emission tunneling and electrostatic accumulation. The device exhibits planar electroluminescence from either positive trion X+ or negative trion X- depending on the bias conditions. We show that hBN serves as a tunneling barrier material allowing selective injection of electron or holes into WSe2 from FLG layer. Our observation offers prospects for hot carrier injection, trion manipulation, and on-chip excitonic devices based on two-dimensional semiconductors.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Monolayer WSe2 exhibits luminescence arising from various types of exciton complexes due to strong many-body effects. Here, we demonstrate selective electrical excitation of positive and negative trions in van der Waals metal-insulator-semiconductor (MIS) heterostructure consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer WSe2. Intentional unbalanced injection of electrons and holes is achieved via field-emission tunneling and electrostatic accumulation. The device exhibits planar electroluminescence from either positive trion X+ or negative trion X- depending on the bias conditions. We show that hBN serves as a tunneling barrier material allowing selective injection of electron or holes into WSe2 from FLG layer. Our observation offers prospects for hot carrier injection, trion manipulation, and on-chip excitonic devices based on two-dimensional semiconductors. |
Shi, Shuyuan; Liang, Shiheng; Zhu, Zhifeng; Cai, Kaiming; Pollard, Shawn D; Wang, Yi; Wang, Junyong; Wang, Qisheng; He, Pan; Yu, Jiawei; Eda, Goki; Liang, Gengchiau; Yang, Hyunsoo All-electric magnetization switching and Dzyaloshinskii-Moriya interaction in WTe2/ferromagnet heterostructures Journal Article NATURE NANOTECHNOLOGY, 14 (10), pp. 945-+, 2019, ISSN: 1748-3387. @article{ISI:000488977100013, title = {All-electric magnetization switching and Dzyaloshinskii-Moriya interaction in WTe_{2}/ferromagnet heterostructures}, author = {Shuyuan Shi and Shiheng Liang and Zhifeng Zhu and Kaiming Cai and Shawn D Pollard and Yi Wang and Junyong Wang and Qisheng Wang and Pan He and Jiawei Yu and Goki Eda and Gengchiau Liang and Hyunsoo Yang}, doi = {10.1038/s41565-019-0525-8}, times_cited = {0}, issn = {1748-3387}, year = {2019}, date = {2019-10-01}, journal = {NATURE NANOTECHNOLOGY}, volume = {14}, number = {10}, pages = {945-+}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {All-electric magnetization manipulation at low power is a prerequisite for a wide adoption of spintronic devices. Materials such as heavy metals(1-3) or topological insulators(4,5) provide good charge-to-spin conversion efficiencies. They enable magnetization switching in heterostructures with either metallic ferromagnets or with magnetic insulators. Recent work suggests a pronounced Edelstein effect in Weyl semimetals due to their non-trivial band structure(6,7); the Edelstein effect can be one order of magnitude stronger than it is in topological insulators or Rashba systems. Furthermore, the strong intrinsic spin Hall effect from the bulk states in Weyl semimetals can contribute to the spin current generation(8). The Td phase of the Weyl semimetal WTe2 (WTe2 hereafter) possesses strong spin-orbit coupling(6,9) and non-trivial band structures(10) with a large spin polarization protected by time-reversal symmetry in both the surface and bulk states(9-11). Atomically flat surfaces, which can be produced with high quality(12), facilitate spintronic device applications. Here, we use WTe2 as a spin current source in WTe2/Ni81Fe19 (Py) heterostructures. We report field-free current-induced magnetization switching at room temperature. A charge current density of similar to 2.96 x 10(5) A cm(-2) suffices to switch the magnetization of the Py layer. With the charge current along the b axis of the WTe2 layer, the thickness-dependent charge-to-spin conversion efficiency reaches 0.51 at 6-7 GHz. At the WTe2/Py interface, a Dzyaloshinskii-Moriya interaction (DMI) with a DMI constant of -1.78 +/- 0.06 mJ m(-2) induces chiral domain wall tilting. Our study demonstrates the capability of WTe2 to efficiently manipulate magnetization and sheds light on the role of the interface in Weyl semimetal/magnet heterostructures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } All-electric magnetization manipulation at low power is a prerequisite for a wide adoption of spintronic devices. Materials such as heavy metals(1-3) or topological insulators(4,5) provide good charge-to-spin conversion efficiencies. They enable magnetization switching in heterostructures with either metallic ferromagnets or with magnetic insulators. Recent work suggests a pronounced Edelstein effect in Weyl semimetals due to their non-trivial band structure(6,7); the Edelstein effect can be one order of magnitude stronger than it is in topological insulators or Rashba systems. Furthermore, the strong intrinsic spin Hall effect from the bulk states in Weyl semimetals can contribute to the spin current generation(8). The Td phase of the Weyl semimetal WTe2 (WTe2 hereafter) possesses strong spin-orbit coupling(6,9) and non-trivial band structures(10) with a large spin polarization protected by time-reversal symmetry in both the surface and bulk states(9-11). Atomically flat surfaces, which can be produced with high quality(12), facilitate spintronic device applications. Here, we use WTe2 as a spin current source in WTe2/Ni81Fe19 (Py) heterostructures. We report field-free current-induced magnetization switching at room temperature. A charge current density of similar to 2.96 x 10(5) A cm(-2) suffices to switch the magnetization of the Py layer. With the charge current along the b axis of the WTe2 layer, the thickness-dependent charge-to-spin conversion efficiency reaches 0.51 at 6-7 GHz. At the WTe2/Py interface, a Dzyaloshinskii-Moriya interaction (DMI) with a DMI constant of -1.78 +/- 0.06 mJ m(-2) induces chiral domain wall tilting. Our study demonstrates the capability of WTe2 to efficiently manipulate magnetization and sheds light on the role of the interface in Weyl semimetal/magnet heterostructures. |
Qin, Ziyu; Loh, Leyi; Wang, Junyong; Xu, Xiaomin; Zhang, Qi; Haas, Benedikt; Alvarez, Carlos; Okuno, Hanako; Yong, Justin Zhou; Schultz, Thorsten; Koch, Norbert; Dan, Jiadong; Pennycook, Stephen J; Zeng, Dawen; Bosman, Michel; Eda, Gold Growth of Nb-Doped Monolayer WS2 by Liquid-Phase Precursor Mixing Journal Article ACS NANO, 13 (9), pp. 10768-10775, 2019, ISSN: 1936-0851. @article{ISI:000487859600097, title = {Growth of Nb-Doped Monolayer WS_{2} by Liquid-Phase Precursor Mixing}, author = {Ziyu Qin and Leyi Loh and Junyong Wang and Xiaomin Xu and Qi Zhang and Benedikt Haas and Carlos Alvarez and Hanako Okuno and Justin Zhou Yong and Thorsten Schultz and Norbert Koch and Jiadong Dan and Stephen J Pennycook and Dawen Zeng and Michel Bosman and Gold Eda}, doi = {10.1021/acsnano.9b05574}, times_cited = {0}, issn = {1936-0851}, year = {2019}, date = {2019-09-01}, journal = {ACS NANO}, volume = {13}, number = {9}, pages = {10768-10775}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Controlled substitutional doping of two-dimensional transition-metal dichalcogenides (TMDs) is of fundamental importance for their applications in electronics and optoelectronics. However, achieving p-type conductivity in MoS2 and WS2 is challenging because of their natural tendency to form n-type vacancy defects. Here, we report versatile growth of p-type monolayer WS2 by liquid-phase mixing of a host tungsten source and niobium dopant. We show that crystallites of WS2 with different concentrations of substitutionally doped Nb up to 10(14) cm(-2) can be grown by reacting solution-deposited precursor film with sulfur vapor at 850 degrees C, reflecting the good miscibility of the precursors in the liquid phase. Atomic-resolution characterization with aberration-corrected scanning transmission electron microscopy reveals that the Nb concentration along the outer edge region of the flakes increases consistently with the molar concentration of Nb in the precursor solution. We further demonstrate that ambipolar field-effect transistors can be fabricated based on Nb-doped monolayer WS2.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Controlled substitutional doping of two-dimensional transition-metal dichalcogenides (TMDs) is of fundamental importance for their applications in electronics and optoelectronics. However, achieving p-type conductivity in MoS2 and WS2 is challenging because of their natural tendency to form n-type vacancy defects. Here, we report versatile growth of p-type monolayer WS2 by liquid-phase mixing of a host tungsten source and niobium dopant. We show that crystallites of WS2 with different concentrations of substitutionally doped Nb up to 10(14) cm(-2) can be grown by reacting solution-deposited precursor film with sulfur vapor at 850 degrees C, reflecting the good miscibility of the precursors in the liquid phase. Atomic-resolution characterization with aberration-corrected scanning transmission electron microscopy reveals that the Nb concentration along the outer edge region of the flakes increases consistently with the molar concentration of Nb in the precursor solution. We further demonstrate that ambipolar field-effect transistors can be fabricated based on Nb-doped monolayer WS2. |