Sow Chorng Haur
Degree: PhD
Position: Vice Dean
Affiliation: NUS – Department of Physics
Research Type: Experiment
Office: S12-02-13
Email: physowch@nus.edu.sg
Contact: (65) 6516 2957
Website: http://www.physics.nus.edu.sg/staff/sowch.html
CA2DM Publications:
2024 |
Lai, Wenhui; Lee, Jong Hak; Shi, Lu; Liu, Yuqing; Pu, Yanhui; Ong, Yong Kang; Limpo, Carlos; Xiong, Ting; Rao, Yifan; Sow, Chorng Haur; Ozyilmaz, Barbaros High mechanical strength Si anode synthesis with interlayer bonded expanded graphite structure for lithium-ion batteries Journal Article JOURNAL OF ENERGY CHEMISTRY, 93 , pp. 253-263, 2024, ISSN: 2095-4956. @article{ISI:001203104900001, title = {High mechanical strength Si anode synthesis with interlayer bonded expanded graphite structure for lithium-ion batteries}, author = {Wenhui Lai and Jong Hak Lee and Lu Shi and Yuqing Liu and Yanhui Pu and Yong Kang Ong and Carlos Limpo and Ting Xiong and Yifan Rao and Chorng Haur Sow and Barbaros Ozyilmaz}, doi = {10.1016/j.jechem.2024.02.021}, times_cited = {4}, issn = {2095-4956}, year = {2024}, date = {2024-03-06}, journal = {JOURNAL OF ENERGY CHEMISTRY}, volume = {93}, pages = {253-263}, publisher = {ELSEVIER}, address = {RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS}, abstract = {Despite advancements in silicon -based anodes for high -capacity lithium -ion batteries, their widespread commercial adoption is still hindered by significant volume expansion during cycling, especially at high active mass loadings crucial for practical use. The root of these challenges lies in the mechanical instability of the material, which subsequently leads to the structural failure of the electrode. Here, we present a novel synthesis of a composite combining expanded graphite and silicon nanoparticles. This composite features a unique interlayer-bonded graphite structure, achieved through the application of a modified spark plasma sintering method. Notably, this innovative structure not only facilitates efficient ion and electron transport but also provides exceptional mechanical strength (Vickers hardness: up to 658 MPa, Young's modulus: 11.6 GPa). This strength effectively accommodates silicon expansion, resulting in an impressive areal capacity of 2.9 mA h cm -2 (736 mA h g-1) and a steady cycle life (93% after 100 cycles). Such outstanding performance is paired with features appropriate for large-scale industrial production of silicon batteries, such as active mass loading of at least 3.9 mg cm -2, a high -tap density electrode material of 1.68 g cm -3 (secondary clusters: 1.12 g cm -3), and a production yield of up to 1 kg per day. (c) 2024 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Despite advancements in silicon -based anodes for high -capacity lithium -ion batteries, their widespread commercial adoption is still hindered by significant volume expansion during cycling, especially at high active mass loadings crucial for practical use. The root of these challenges lies in the mechanical instability of the material, which subsequently leads to the structural failure of the electrode. Here, we present a novel synthesis of a composite combining expanded graphite and silicon nanoparticles. This composite features a unique interlayer-bonded graphite structure, achieved through the application of a modified spark plasma sintering method. Notably, this innovative structure not only facilitates efficient ion and electron transport but also provides exceptional mechanical strength (Vickers hardness: up to 658 MPa, Young's modulus: 11.6 GPa). This strength effectively accommodates silicon expansion, resulting in an impressive areal capacity of 2.9 mA h cm -2 (736 mA h g-1) and a steady cycle life (93% after 100 cycles). Such outstanding performance is paired with features appropriate for large-scale industrial production of silicon batteries, such as active mass loading of at least 3.9 mg cm -2, a high -tap density electrode material of 1.68 g cm -3 (secondary clusters: 1.12 g cm -3), and a production yield of up to 1 kg per day. (c) 2024 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved. |
2023 |
Zhang, Hanwen; Poh, Eng Tuan; Lim, Sharon Xiaodai; Zhang, Yimin; Qin, Hongye; Xie, Haonan; He, Chunnian; Sow, Chorng Haur In situ strain-induced phase transition and defect engineering in CVD-synthesized atomically thin MoS2 Journal Article 2D MATERIALS, 10 (3), 2023, ISSN: 2053-1583. @article{ISI:000994586300001, title = {\textit{In situ} strain-induced phase transition and defect engineering in CVD-synthesized atomically thin MoS_{2}}, author = {Hanwen Zhang and Eng Tuan Poh and Sharon Xiaodai Lim and Yimin Zhang and Hongye Qin and Haonan Xie and Chunnian He and Chorng Haur Sow}, doi = {10.1088/2053-1583/acd0be}, times_cited = {6}, issn = {2053-1583}, year = {2023}, date = {2023-07-01}, journal = {2D MATERIALS}, volume = {10}, number = {3}, publisher = {IOP Publishing Ltd}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {Alkali metal halides have recently received great attention as additives in the chemical vapor deposition (CVD) process to promote the growth of transition metal dichalcogenides (TMDs). However, the multi-faceted role of these halide salts in modulating the properties and quality of TMD monolayers remains mechanistically unclear. In this study, by introducing excessive gaseous sodium chloride (NaCl) into the CVD system, we demonstrate that preferential NaCl deposition along the monolayer edges causes large in situ strain that can invoke localized domains of high defect density and 2H to 1T phase transition. High-resolution scanning transmission electron microscopy, Raman mapping and molecular dynamics simulations revealed that higher NaCl concentrations can promote the coalescence of independent local strain domains, further increasing the 1T/2H phase ratio and defect density. Furthermore, excessive NaCl was also proven by density functional theory calculations to convert thermodynamic growth to kinetic growth, accounting for the unique cloud-shaped MoS2 crystals acquired. Compared with post-growth strain processing methods, this one-step approach for phase and defect engineering not only represents a deeper understanding of the role that NaCl plays in the CVD process, but also provides a convenient means to controllably synthesize conductive/defect-rich materials for further electrocatalysis and optoelectronic applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Alkali metal halides have recently received great attention as additives in the chemical vapor deposition (CVD) process to promote the growth of transition metal dichalcogenides (TMDs). However, the multi-faceted role of these halide salts in modulating the properties and quality of TMD monolayers remains mechanistically unclear. In this study, by introducing excessive gaseous sodium chloride (NaCl) into the CVD system, we demonstrate that preferential NaCl deposition along the monolayer edges causes large in situ strain that can invoke localized domains of high defect density and 2H to 1T phase transition. High-resolution scanning transmission electron microscopy, Raman mapping and molecular dynamics simulations revealed that higher NaCl concentrations can promote the coalescence of independent local strain domains, further increasing the 1T/2H phase ratio and defect density. Furthermore, excessive NaCl was also proven by density functional theory calculations to convert thermodynamic growth to kinetic growth, accounting for the unique cloud-shaped MoS2 crystals acquired. Compared with post-growth strain processing methods, this one-step approach for phase and defect engineering not only represents a deeper understanding of the role that NaCl plays in the CVD process, but also provides a convenient means to controllably synthesize conductive/defect-rich materials for further electrocatalysis and optoelectronic applications. |
2022 |
Chen, Bochao; Zhang, Hanwen; Liang, Ming; Wang, Yuxuan; Wu, Zhiyi; Zhu, Shan; Shi, Chunsheng; Zhao, Naiqin; Liu, Enzuo; Sow, Chorng Haur; He, Chunnian NaCl-pinned antimony nanoparticles combined with ion-shuttle-induced graphitized 3D carbon to boost sodium storage Journal Article CELL REPORTS PHYSICAL SCIENCE, 3 (5), 2022. @article{ISI:000840855100006, title = {NaCl-pinned antimony nanoparticles combined with ion-shuttle-induced graphitized 3D carbon to boost sodium storage}, author = {Bochao Chen and Hanwen Zhang and Ming Liang and Yuxuan Wang and Zhiyi Wu and Shan Zhu and Chunsheng Shi and Naiqin Zhao and Enzuo Liu and Chorng Haur Sow and Chunnian He}, doi = {10.1016/j.xcrp.2022.100891}, times_cited = {5}, year = {2022}, date = {2022-05-18}, journal = {CELL REPORTS PHYSICAL SCIENCE}, volume = {3}, number = {5}, publisher = {CELL PRESS}, address = {50 HAMPSHIRE ST, FLOOR 5, CAMBRIDGE, MA 02139 USA}, abstract = {Abundant sodium resources provide compelling competitive advantage for sodium-ion battery (SIBs) applications. Correspondingly, it is urgently required to develop high-performance and low-cost anode materials for SIBs. Here, we report a composite of antimony nanoparticles anchored on N/S co-doped 3D carbon for superior SIB anodes. During the synthesis, NaCl exerts a "pinning effect" to restrict the growth of antimony in the carbon matrix and results in nano-sized antimony particles. Given the enhanced-charge/ion-transfer kinetics ensured by nano-Sb and the structural advantages derived from the N/S co-doped 3D porous carbon, which not only remain robust upon cycling but also undergo graphitization by the ion shuttle effect to stimulate a stronger electrochemical response during the activation process, this composite maintains a 98.9% capacity ratio over 20,000 cycles at 10 A g(-1) Furthermore, molecular dynamics simulations reveal that the degree of graphitization has a linear relationship with the ionic radius.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Abundant sodium resources provide compelling competitive advantage for sodium-ion battery (SIBs) applications. Correspondingly, it is urgently required to develop high-performance and low-cost anode materials for SIBs. Here, we report a composite of antimony nanoparticles anchored on N/S co-doped 3D carbon for superior SIB anodes. During the synthesis, NaCl exerts a "pinning effect" to restrict the growth of antimony in the carbon matrix and results in nano-sized antimony particles. Given the enhanced-charge/ion-transfer kinetics ensured by nano-Sb and the structural advantages derived from the N/S co-doped 3D porous carbon, which not only remain robust upon cycling but also undergo graphitization by the ion shuttle effect to stimulate a stronger electrochemical response during the activation process, this composite maintains a 98.9% capacity ratio over 20,000 cycles at 10 A g(-1) Furthermore, molecular dynamics simulations reveal that the degree of graphitization has a linear relationship with the ionic radius. |
Wang, Xinyun; Zhao, Yuzhou; Kong, Xiao; Zhang, Qi; Ng, Hong Kuan; Lim, Sharon Xiaodai; Zheng, Yue; Wu, Xiao; Watanabe, Kenji; Xu, Qing-Hua; Taniguchi, Takashi; Eda, Goki; Goh, Kuan Eng Johnson; Jin, Song; Loh, Kian Ping; Ding, Feng; Sun, Wanxin; Sow, Chorng Haur Dynamic Tuning of Moire Superlattice Morphology by Laser Modification Journal Article ACS NANO, 16 (5), pp. 8172-8180, 2022, ISSN: 1936-0851. @article{ISI:000820334500001, title = {Dynamic Tuning of Moire Superlattice Morphology by Laser Modification}, author = {Xinyun Wang and Yuzhou Zhao and Xiao Kong and Qi Zhang and Hong Kuan Ng and Sharon Xiaodai Lim and Yue Zheng and Xiao Wu and Kenji Watanabe and Qing-Hua Xu and Takashi Taniguchi and Goki Eda and Kuan Eng Johnson Goh and Song Jin and Kian Ping Loh and Feng Ding and Wanxin Sun and Chorng Haur Sow}, doi = {10.1021/acsnano.2c01625}, times_cited = {5}, issn = {1936-0851}, year = {2022}, date = {2022-05-16}, journal = {ACS NANO}, volume = {16}, number = {5}, pages = {8172-8180}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {In artificial van der Waals (vdW) layered devices, twisting the stacking angle has emerged as an effective strategy to regulate the electronic phases and optical properties of these systems. Along with the twist registry, the lattice reconstruction arising from vdW interlayer interaction has also inspired significant research interests. The control of twist angles is significantly important because the moire periodicity determines the electron propagation length on the lattice and the interlayer electron-electron interactions. However, the moire periodicity is hard to be modified after the device has been fabricated. In this work, we have demonstrated that the moire periodicity can be precisely modulated with a localized laser annealing technique. This is achieved with regulating the interlayer lattice mismatch by the mismatched lattice constant, which originates from the variable density of sulfur vacancy generated during laser modification. The existence of sulfur vacancy is further verified by excitonic emission energy and lifetime in photoluminescence measurements. Furthermore, we also discover that the mismatched lattice constant has the equivalent contribution as the twist angle for determining the lattice mismatch. Theoretical modeling elaborates the moire-wavelength-dependent energy variations at the interface and mimics the evolution of moire morphology.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In artificial van der Waals (vdW) layered devices, twisting the stacking angle has emerged as an effective strategy to regulate the electronic phases and optical properties of these systems. Along with the twist registry, the lattice reconstruction arising from vdW interlayer interaction has also inspired significant research interests. The control of twist angles is significantly important because the moire periodicity determines the electron propagation length on the lattice and the interlayer electron-electron interactions. However, the moire periodicity is hard to be modified after the device has been fabricated. In this work, we have demonstrated that the moire periodicity can be precisely modulated with a localized laser annealing technique. This is achieved with regulating the interlayer lattice mismatch by the mismatched lattice constant, which originates from the variable density of sulfur vacancy generated during laser modification. The existence of sulfur vacancy is further verified by excitonic emission energy and lifetime in photoluminescence measurements. Furthermore, we also discover that the mismatched lattice constant has the equivalent contribution as the twist angle for determining the lattice mismatch. Theoretical modeling elaborates the moire-wavelength-dependent energy variations at the interface and mimics the evolution of moire morphology. |
2021 |
Ma, Yaping; Shao, Xiji; Li, Jing; Dong, Bowei; Hu, Zhenliang; Zhou, Qiulan; Xu, Haomin; Zhao, Xiaoxu; Fang, Hanyan; Li, Xinzhe; Li, Zejun; Wu, Jing; Zhao, Meng; Pennycook, Stephen John; Sow, Chorng Haur; Lee, Chengkuo; Zhong, Yu Lin; Lu, Junpeng; Ding, Mengning; Wang, Kedong; Li, Ying; Lu, Jiong Electrochemically Exfoliated Platinum Dichalcogenide Atomic Layers for High-Performance Air-Stable Infrared Photodetectors Journal Article 32 ACS APPLIED MATERIALS & INTERFACES, 13 (7), pp. 8518-8527, 2021, ISSN: 1944-8244. @article{ISI:000623228500064, title = {Electrochemically Exfoliated Platinum Dichalcogenide Atomic Layers for High-Performance Air-Stable Infrared Photodetectors}, author = {Yaping Ma and Xiji Shao and Jing Li and Bowei Dong and Zhenliang Hu and Qiulan Zhou and Haomin Xu and Xiaoxu Zhao and Hanyan Fang and Xinzhe Li and Zejun Li and Jing Wu and Meng Zhao and Stephen John Pennycook and Chorng Haur Sow and Chengkuo Lee and Yu Lin Zhong and Junpeng Lu and Mengning Ding and Kedong Wang and Ying Li and Jiong Lu}, doi = {10.1021/acsami.0c20535}, times_cited = {32}, issn = {1944-8244}, year = {2021}, date = {2021-02-11}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {13}, number = {7}, pages = {8518-8527}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Platinum dichalcogenide (PtX2), an emergent group-10 transition metal dichalcogenide (TMD) has shown great potential in infrared photonic and optoelectronic applications due to its layer-dependent electronic structure with potentially suitable bandgap. However, a scalable synthesis of PtSe2 and PtTe2 atomic layers with controlled thickness still represents a major challenge in this field because of the strong interlayer interactions. Herein, we develop a facile cathodic exfoliation approach for the synthesis of solution-processable high-quality PtSe2 and PtTe2 atomic layers for high-performance infrared (IR) photodetection. As-exfoliated PtSe2 and PtTe2 bilayer exhibit an excellent photoresponsivity of 72 and 1620 mA W-1 at zero gate voltage under a 1540 nm laser illumination, respectively, approximately several orders of magnitude higher than that of the majority of IR photodetectors based on graphene, TMDs, and black phosphorus. In addition, our PtSe2 and PtTe2 bilayer device also shows a decent specific detectivity of beyond 10(9) Jones with remarkable air-stability (>several months), outperforming the mechanically exfoliated counterparts under the laser illumination with a similar wavelength. Moreover, a high yield of PtSe2 and PtTe2 atomic layers dispersed in solution also allows for a facile fabrication of air-stable wafer-scale IR photodetector. This work demonstrates a new route for the synthesis of solution-processable layered materials with the narrow bandgap for the infrared optoelectronic applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Platinum dichalcogenide (PtX2), an emergent group-10 transition metal dichalcogenide (TMD) has shown great potential in infrared photonic and optoelectronic applications due to its layer-dependent electronic structure with potentially suitable bandgap. However, a scalable synthesis of PtSe2 and PtTe2 atomic layers with controlled thickness still represents a major challenge in this field because of the strong interlayer interactions. Herein, we develop a facile cathodic exfoliation approach for the synthesis of solution-processable high-quality PtSe2 and PtTe2 atomic layers for high-performance infrared (IR) photodetection. As-exfoliated PtSe2 and PtTe2 bilayer exhibit an excellent photoresponsivity of 72 and 1620 mA W-1 at zero gate voltage under a 1540 nm laser illumination, respectively, approximately several orders of magnitude higher than that of the majority of IR photodetectors based on graphene, TMDs, and black phosphorus. In addition, our PtSe2 and PtTe2 bilayer device also shows a decent specific detectivity of beyond 10(9) Jones with remarkable air-stability (>several months), outperforming the mechanically exfoliated counterparts under the laser illumination with a similar wavelength. Moreover, a high yield of PtSe2 and PtTe2 atomic layers dispersed in solution also allows for a facile fabrication of air-stable wafer-scale IR photodetector. This work demonstrates a new route for the synthesis of solution-processable layered materials with the narrow bandgap for the infrared optoelectronic applications. |
2019 |
Poh, Eng Tuan; Liu, Xiaogang; Sow, Chorng Haur Laser-Guided Microcanvas Printing of Multicolor Upconversion Nanoparticles on Molybdenum Disulfide Monolayer Journal Article ADVANCED MATERIALS INTERFACES, 6 (24), 2019, ISSN: 2196-7350. @article{ISI:000497859700001, title = {Laser-Guided Microcanvas Printing of Multicolor Upconversion Nanoparticles on Molybdenum Disulfide Monolayer}, author = {Eng Tuan Poh and Xiaogang Liu and Chorng Haur Sow}, doi = {10.1002/admi.201901673}, times_cited = {5}, issn = {2196-7350}, year = {2019}, date = {2019-11-22}, journal = {ADVANCED MATERIALS INTERFACES}, volume = {6}, number = {24}, publisher = {WILEY}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {Scanning focused laser beams incident on nanomaterials have provided a nondestructive and facile technique to fabricate micropatterns of a wide variety of hybrid materials. Conventionally, the technique is limited to localized chemical modification or in situ reduction of specific metal ions en route to heterogeneous material systems. However, as hybrid structures continue to be an essential form to couple various material properties and bring forth nanostructures with designable traits, the need for a flexible technique to interface nanomaterials presynthesized in higher quality remains an important challenge. Herein, a technique for laser-guided microcanvas formation by anchoring preformed upconversion nanoparticles at specific sites on a MoS2 monolayer surface is presented. The technique expands the building blocks in laser-produced hybrid structures to include presynthesized nanomaterials. The upconversion microstructures are formed via a microbubble-assisted mechanism, with distinct emission contrast against the background. The proof-of-concept production of a multicolor upconversion microcanvas marks the potential for full-color high-resolution displays while the technique opens up the possibility of fabricating an expandable range of new hybrid structures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Scanning focused laser beams incident on nanomaterials have provided a nondestructive and facile technique to fabricate micropatterns of a wide variety of hybrid materials. Conventionally, the technique is limited to localized chemical modification or in situ reduction of specific metal ions en route to heterogeneous material systems. However, as hybrid structures continue to be an essential form to couple various material properties and bring forth nanostructures with designable traits, the need for a flexible technique to interface nanomaterials presynthesized in higher quality remains an important challenge. Herein, a technique for laser-guided microcanvas formation by anchoring preformed upconversion nanoparticles at specific sites on a MoS2 monolayer surface is presented. The technique expands the building blocks in laser-produced hybrid structures to include presynthesized nanomaterials. The upconversion microstructures are formed via a microbubble-assisted mechanism, with distinct emission contrast against the background. The proof-of-concept production of a multicolor upconversion microcanvas marks the potential for full-color high-resolution displays while the technique opens up the possibility of fabricating an expandable range of new hybrid structures. |
Wang, Xinyun; Dan, Jiadong; Hu, Zhenliang; Leong, Jin Feng; Zhang, Qi; Qin, Ziyu; Li, Shisheng; Lu, Junpeng; Pennycook, Stephen J; Sun, Wanxin; Sow, Chorng Haur Defect Heterogeneity in Monolayer WS2 Unveiled by Work Function Variance Journal Article 43 CHEMISTRY OF MATERIALS, 31 (19), pp. 7970-7978, 2019, ISSN: 0897-4756. @article{ISI:000489678800017, title = {Defect Heterogeneity in Monolayer WS_{2} Unveiled by Work Function Variance}, author = {Xinyun Wang and Jiadong Dan and Zhenliang Hu and Jin Feng Leong and Qi Zhang and Ziyu Qin and Shisheng Li and Junpeng Lu and Stephen J Pennycook and Wanxin Sun and Chorng Haur Sow}, doi = {10.1021/acs.chemmater.9b02157}, times_cited = {43}, issn = {0897-4756}, year = {2019}, date = {2019-10-08}, journal = {CHEMISTRY OF MATERIALS}, volume = {31}, number = {19}, pages = {7970-7978}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Defects are commonly found in two-dimensional (2D) transition-metal dichalcogenide (TMD) materials. Such defects usually dictate the optical and electrical properties of TMDs. It is thus important to develop techniques to characterize the defects directly with good spatial resolution, specificity, and throughput. Herein, we demonstrate that Kelvin probe force microscopy (KPFM) is a versatile technique for this task. It is able to unveil defect heterogeneity of 2D materials with a spatial resolution of 10 nm and energy sensitivity better than 10 meV. KPFM mappings of monolayer WS2 exhibit interesting work function variances that are associated with defects distribution. This finding is verified by aberration-corrected scanning transmission electron microscopy and density functional theory calculations. In particular, a strong correlation among the work function, electrical and optical responses to the defects is revealed. Our findings demonstrate the potential of KPFM as an effective tool for exploring the intrinsic defects in TMDs.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Defects are commonly found in two-dimensional (2D) transition-metal dichalcogenide (TMD) materials. Such defects usually dictate the optical and electrical properties of TMDs. It is thus important to develop techniques to characterize the defects directly with good spatial resolution, specificity, and throughput. Herein, we demonstrate that Kelvin probe force microscopy (KPFM) is a versatile technique for this task. It is able to unveil defect heterogeneity of 2D materials with a spatial resolution of 10 nm and energy sensitivity better than 10 meV. KPFM mappings of monolayer WS2 exhibit interesting work function variances that are associated with defects distribution. This finding is verified by aberration-corrected scanning transmission electron microscopy and density functional theory calculations. In particular, a strong correlation among the work function, electrical and optical responses to the defects is revealed. Our findings demonstrate the potential of KPFM as an effective tool for exploring the intrinsic defects in TMDs. |
Hu, Zhenliang; Avila, Jose; Wang, Xinyun; Leong, Jin Feng; Zhang, Qi; Liu, Yanpeng; Asensio, Maria C; Lu, Junpeng; Carvalho, Alexandra; Sow, Chorng Haur; Neto, Antonio Helio Castro The Role of Oxygen Atoms on Excitons at the Edges of Monolayer WS2 Journal Article 51 NANO LETTERS, 19 (7), pp. 4641-4650, 2019, ISSN: 1530-6984. @article{ISI:000475533900056, title = {The Role of Oxygen Atoms on Excitons at the Edges of Monolayer WS_{2}}, author = {Zhenliang Hu and Jose Avila and Xinyun Wang and Jin Feng Leong and Qi Zhang and Yanpeng Liu and Maria C Asensio and Junpeng Lu and Alexandra Carvalho and Chorng Haur Sow and Antonio Helio Castro Neto}, doi = {10.1021/acs.nanolett.9b01670}, times_cited = {51}, issn = {1530-6984}, year = {2019}, date = {2019-07-01}, journal = {NANO LETTERS}, volume = {19}, number = {7}, pages = {4641-4650}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {We clarify that the chemisorption of oxygen atoms at the edges is a key contributor to the frequently observed edge enhancement and spatial non-uniformities of photoluminescence (PL) in WS2 monolayers. Here we have investigated with momentum- and real-space nanoimaging of the chemical and electronic density inhomogeneity of WS2 flakes. Our finding from a large panoply of techniques together with density functional theory calculation confirms that the oxygen chemisorption leads to the electron accumulation at the edges. This facilitates the trion dominance of PL at the edges of WS2 flakes. Our results highlight and unravel the significance of chemisorbed oxygen at the edges in the PL emission and electronic structure of WS2, providing a viable path to enhance the performance of transition-metal-dichalcogenide-based devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We clarify that the chemisorption of oxygen atoms at the edges is a key contributor to the frequently observed edge enhancement and spatial non-uniformities of photoluminescence (PL) in WS2 monolayers. Here we have investigated with momentum- and real-space nanoimaging of the chemical and electronic density inhomogeneity of WS2 flakes. Our finding from a large panoply of techniques together with density functional theory calculation confirms that the oxygen chemisorption leads to the electron accumulation at the edges. This facilitates the trion dominance of PL at the edges of WS2 flakes. Our results highlight and unravel the significance of chemisorbed oxygen at the edges in the PL emission and electronic structure of WS2, providing a viable path to enhance the performance of transition-metal-dichalcogenide-based devices. |
2018 |
Gong, Lili; Zhang, Qi; Wang, Liangjun; Wu, Jianfeng; Han, Cheng; Lei, Bo; Chen, Wei; Eda, Goki; Goh, Kuan Eng Johnson; Sow, Chorng Haur Emergence of photoluminescence on bulk MoS2 by laser thinning and gold particle decoration Journal Article 45 NANO RESEARCH, 11 (9), pp. 4574-4586, 2018, ISSN: 1998-0124. @article{ISI:000441237100010, title = {Emergence of photoluminescence on bulk MoS_{2} by laser thinning and gold particle decoration}, author = {Lili Gong and Qi Zhang and Liangjun Wang and Jianfeng Wu and Cheng Han and Bo Lei and Wei Chen and Goki Eda and Kuan Eng Johnson Goh and Chorng Haur Sow}, doi = {10.1007/s12274-018-2037-5}, times_cited = {45}, issn = {1998-0124}, year = {2018}, date = {2018-09-01}, journal = {NANO RESEARCH}, volume = {11}, number = {9}, pages = {4574-4586}, publisher = {TSINGHUA UNIV PRESS}, address = {B605D, XUE YAN BUILDING, BEIJING, 100084, PEOPLES R CHINA}, abstract = {We demonstrate a facile and effective approach to significantly improve the photoluminescence of bulk MoS2 via laser thinning followed by gold particle decoration. Upon laser thinning of exfoliated bulk MoS2, photoluminescence emerges from the laser-thinned region. After further treatment with an AuCl3 solution, gold particles self-assemble on the laser-thinned region and thick edges, further increasing the fluorescence of bulk MoS2 28 times and the Raman response 3 times. Such fluorescence enhancement can be attributed to both surface plasmon resonance and p-type doping induced by gold particles. The combination of laser thinning and AuCl3 treatment enables the functionalization of bulk MoS2 for optoelectronic applications. It can also provide a viable strategy for mask-free and area-selective p-type doping on single MoS2 flakes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We demonstrate a facile and effective approach to significantly improve the photoluminescence of bulk MoS2 via laser thinning followed by gold particle decoration. Upon laser thinning of exfoliated bulk MoS2, photoluminescence emerges from the laser-thinned region. After further treatment with an AuCl3 solution, gold particles self-assemble on the laser-thinned region and thick edges, further increasing the fluorescence of bulk MoS2 28 times and the Raman response 3 times. Such fluorescence enhancement can be attributed to both surface plasmon resonance and p-type doping induced by gold particles. The combination of laser thinning and AuCl3 treatment enables the functionalization of bulk MoS2 for optoelectronic applications. It can also provide a viable strategy for mask-free and area-selective p-type doping on single MoS2 flakes. |
Liu, Yanpeng; Rodrigues, J N B; Luo, Yong Zheng; Li, Linjun; Carvalho, Alexandra; Yang, Ming; Laksono, Evan; Lu, Junpeng; Bao, Yang; Xu, Hai; Tan, Sherman J R; Qiu, Zhizhan; Sow, Chorng Haur; Feng, Yuan Ping; Neto, Castro A H; Adam, Shaffique; Lu, Jiong; Loh, Kian Ping Tailoring sample-wide pseudo-magnetic fields on a graphene-black phosphorus heterostructure Journal Article 139 NATURE NANOTECHNOLOGY, 13 (9), pp. 828-+, 2018, ISSN: 1748-3387. @article{ISI:000443851800019, title = {Tailoring sample-wide pseudo-magnetic fields on a graphene-black phosphorus heterostructure}, author = {Yanpeng Liu and J N B Rodrigues and Yong Zheng Luo and Linjun Li and Alexandra Carvalho and Ming Yang and Evan Laksono and Junpeng Lu and Yang Bao and Hai Xu and Sherman J R Tan and Zhizhan Qiu and Chorng Haur Sow and Yuan Ping Feng and Castro A H Neto and Shaffique Adam and Jiong Lu and Kian Ping Loh}, doi = {10.1038/s41565-018-0178-z}, times_cited = {139}, issn = {1748-3387}, year = {2018}, date = {2018-09-01}, journal = {NATURE NANOTECHNOLOGY}, volume = {13}, number = {9}, pages = {828-+}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Spatially tailored pseudo-magnetic fields (PMFs) can give rise to pseudo-Landau levels and the valley Hall effect in graphene. At an experimental level, it is highly challenging to create the specific strain texture that can generate PMFs over large areas. Here, we report that superposing graphene on multilayer black phosphorus creates shear-strained superlattices that generate a PMF over an entire graphene-black phosphorus heterostructure with edge size of tens of micrometres. The PMF is intertwined with the spatial period of the moire pattern, and its spatial distribution and intensity can be modified by changing the relative orientation of the two materials. We show that the emerging pseudo-Landau levels influence the transport properties of graphene-black phosphorus field-effect transistor devices with Hall bar geometry. The application of an external magnetic field allows us to enhance or reduce the effective field depending on the valley polarization with the prospect of developing a valley filter.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Spatially tailored pseudo-magnetic fields (PMFs) can give rise to pseudo-Landau levels and the valley Hall effect in graphene. At an experimental level, it is highly challenging to create the specific strain texture that can generate PMFs over large areas. Here, we report that superposing graphene on multilayer black phosphorus creates shear-strained superlattices that generate a PMF over an entire graphene-black phosphorus heterostructure with edge size of tens of micrometres. The PMF is intertwined with the spatial period of the moire pattern, and its spatial distribution and intensity can be modified by changing the relative orientation of the two materials. We show that the emerging pseudo-Landau levels influence the transport properties of graphene-black phosphorus field-effect transistor devices with Hall bar geometry. The application of an external magnetic field allows us to enhance or reduce the effective field depending on the valley polarization with the prospect of developing a valley filter. |
2017 |
Gogoi, Pranjal Kumar; Hu, Zhenliang; Wang, Qixing; Carvalho, Alexandra; Schmidt, Daniel; Yin, Xinmao; Chang, Yung-Huang; Li, Lain-Jong; Sow, Chorng Haur; Neto, Castro A H; Breese, Mark B H; Rusydi, Andrivo; Wee, Andrew T S Oxygen Passivation Mediated Tunability of Trion and Excitons in MoS2 Journal Article 68 PHYSICAL REVIEW LETTERS, 119 (7), 2017, ISSN: 0031-9007. @article{ISI:000407719400012, title = {Oxygen Passivation Mediated Tunability of Trion and Excitons in MoS_{2}}, author = {Pranjal Kumar Gogoi and Zhenliang Hu and Qixing Wang and Alexandra Carvalho and Daniel Schmidt and Xinmao Yin and Yung-Huang Chang and Lain-Jong Li and Chorng Haur Sow and Castro A H Neto and Mark B H Breese and Andrivo Rusydi and Andrew T S Wee}, doi = {10.1103/PhysRevLett.119.077402}, times_cited = {68}, issn = {0031-9007}, year = {2017}, date = {2017-08-16}, journal = {PHYSICAL REVIEW LETTERS}, volume = {119}, number = {7}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Using wide spectral range in situ spectroscopic ellipsometry with systematic ultrahigh vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS2 isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A (1.92 eV) and B (2.02 eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the band structure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This Letter unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS2.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Using wide spectral range in situ spectroscopic ellipsometry with systematic ultrahigh vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS2 isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A (1.92 eV) and B (2.02 eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the band structure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This Letter unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS2. |
Sow, Belle Miaoer; Lu, Junpeng; Liu, Hongwei; Goh, Kuan Eng Johnson; Sow, Chorng Haur Enriched Fluorescence Emission from WS2 Monoflake Empowered by Au Nanoexplorers Journal Article 11 ADVANCED OPTICAL MATERIALS, 5 (14), 2017, ISSN: 2195-1071. @article{ISI:000406140200007, title = {Enriched Fluorescence Emission from WS_{2} Monoflake Empowered by Au Nanoexplorers}, author = {Belle Miaoer Sow and Junpeng Lu and Hongwei Liu and Kuan Eng Johnson Goh and Chorng Haur Sow}, doi = {10.1002/adom.201700156}, times_cited = {11}, issn = {2195-1071}, year = {2017}, date = {2017-07-17}, journal = {ADVANCED OPTICAL MATERIALS}, volume = {5}, number = {14}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Gold nanoparticles (Au NPs) are deposited on monolayer 2D tungsten disulfide (WS2) microflake (monoflake) to probe the effects of gold deposition on the physical and chemical properties of the WS2 transition metal dichalcogenides. It is found that the Au NPs behave like nanoexplorers that map out subtle and hidden chemical heterogeneity within the WS2 monoflake by way of site-selective decoration on the WS2 monoflake. The resultant decorated Au NPs patterns trace the concentric fluorescence pattern found on the WS2 monoflake. The Au NPs enhance the fluorescence intensity in selected regions within the WS2 monoflake and even activate fluorescence emission from previously dark regions. Most remarkably, the photoluminescence spectra from WS2 with Au NPs are sharpened and dominated by neutral excitons. This is in stark contrast to photoluminescence emission from pristine WS2 monoflake where the spectrum exhibits a multitude of emissions from trions, biexcitons, neutral excitons, and defect-bounded excitons.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Gold nanoparticles (Au NPs) are deposited on monolayer 2D tungsten disulfide (WS2) microflake (monoflake) to probe the effects of gold deposition on the physical and chemical properties of the WS2 transition metal dichalcogenides. It is found that the Au NPs behave like nanoexplorers that map out subtle and hidden chemical heterogeneity within the WS2 monoflake by way of site-selective decoration on the WS2 monoflake. The resultant decorated Au NPs patterns trace the concentric fluorescence pattern found on the WS2 monoflake. The Au NPs enhance the fluorescence intensity in selected regions within the WS2 monoflake and even activate fluorescence emission from previously dark regions. Most remarkably, the photoluminescence spectra from WS2 with Au NPs are sharpened and dominated by neutral excitons. This is in stark contrast to photoluminescence emission from pristine WS2 monoflake where the spectrum exhibits a multitude of emissions from trions, biexcitons, neutral excitons, and defect-bounded excitons. |
Venkatakrishnan, Ashwin; Chua, Hou; Tan, Pinxi; Hu, Zhenliang; Liu, Hongwei; Liu, Yanpeng; Carvalho, Alexandra; Lu, Junpeng; Sow, Chorng Haur Microsteganography on WS2 Monolayers Tailored by Direct Laser Painting Journal Article 51 ACS NANO, 11 (1), pp. 713-720, 2017, ISSN: 1936-0851. @article{ISI:000392886500073, title = {Microsteganography on WS_{2} Monolayers Tailored by Direct Laser Painting}, author = {Ashwin Venkatakrishnan and Hou Chua and Pinxi Tan and Zhenliang Hu and Hongwei Liu and Yanpeng Liu and Alexandra Carvalho and Junpeng Lu and Chorng Haur Sow}, doi = {10.1021/acsnano.6b07118}, times_cited = {51}, issn = {1936-0851}, year = {2017}, date = {2017-01-01}, journal = {ACS NANO}, volume = {11}, number = {1}, pages = {713-720}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {We present scanning focused laser beam as a multipurpose tool to engineer the physical and chemical properties of WS2 microflakes. For monolayers, the laser modification integrates oxygen into the WS2 microflake, resulting in similar to 9 times enhancement in the intensity of the fluorescence emission. This modification does not cause any morphology change, allowing "micro-encryption" of information that is only observable as fluorescence under excitation. The same focused laser also facilitates on demand thinning down of WS2 multilayers into monolayers, turning them into fluorescence active components. With, a scanning focused laser beam, micropatterns are readily created on WS, multilayers through selective thinning of specific regions on the flake.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present scanning focused laser beam as a multipurpose tool to engineer the physical and chemical properties of WS2 microflakes. For monolayers, the laser modification integrates oxygen into the WS2 microflake, resulting in similar to 9 times enhancement in the intensity of the fluorescence emission. This modification does not cause any morphology change, allowing "micro-encryption" of information that is only observable as fluorescence under excitation. The same focused laser also facilitates on demand thinning down of WS2 multilayers into monolayers, turning them into fluorescence active components. With, a scanning focused laser beam, micropatterns are readily created on WS, multilayers through selective thinning of specific regions on the flake. |
2016 |
Lu, Junpeng; Carvalho, Alexandra; Liu, Hongwei; Lim, Sharon Xiaodai; Neto, Antonio Castro H; Sow, Chorng Haur Hybrid Bilayer WSe2-CH3NH3PbI3 Organolead Halide Perovskite as a High-Performance Photodetector Journal Article 98 ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 55 (39), pp. 11945-11949, 2016, ISSN: 1433-7851. @article{ISI:000384713100043, title = {Hybrid Bilayer WSe_{2}-CH_{3}NH_{3}PbI_{3} Organolead Halide Perovskite as a High-Performance Photodetector}, author = {Junpeng Lu and Alexandra Carvalho and Hongwei Liu and Sharon Xiaodai Lim and Antonio Castro H Neto and Chorng Haur Sow}, doi = {10.1002/anie.201603557}, times_cited = {98}, issn = {1433-7851}, year = {2016}, date = {2016-09-19}, journal = {ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, volume = {55}, number = {39}, pages = {11945-11949}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {A high-performance 2D photodetector based on a bilayer structure comprising a WSe2 monolayer and CH3NH3PbI3 organolead halide perovskite is reported. High performance is realized by modification of the WSe2 monolayer with laser healing and perovskite functionalization. After modification, the output of the device was three orders of magnitude better than the pristine device; the performance is superior to that of most of the 2D photodetectors based on transition-metal-dichalcogenides (TMDs). This result indicates that combinatory TMDs-halide perovskite hybrids can be promising building blocks in optoelectronics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A high-performance 2D photodetector based on a bilayer structure comprising a WSe2 monolayer and CH3NH3PbI3 organolead halide perovskite is reported. High performance is realized by modification of the WSe2 monolayer with laser healing and perovskite functionalization. After modification, the output of the device was three orders of magnitude better than the pristine device; the performance is superior to that of most of the 2D photodetectors based on transition-metal-dichalcogenides (TMDs). This result indicates that combinatory TMDs-halide perovskite hybrids can be promising building blocks in optoelectronics. |
Liu, Hongwei; Lu, Junpeng; Ho, Kenneth; Hu, Zhenliang; Dang, Zhiya; Carvalho, Alexandra; Tan, Hui Ru; Tok, Eng Soon; Sow, Chorng Haur Fluorescence Concentric Triangles: A Case of Chemical Heterogeneity in WS2 Atomic Monolayer Journal Article 83 NANO LETTERS, 16 (9), pp. 5559-5567, 2016, ISSN: 1530-6984. @article{ISI:000383412100037, title = {Fluorescence Concentric Triangles: A Case of Chemical Heterogeneity in WS_{2} Atomic Monolayer}, author = {Hongwei Liu and Junpeng Lu and Kenneth Ho and Zhenliang Hu and Zhiya Dang and Alexandra Carvalho and Hui Ru Tan and Eng Soon Tok and Chorng Haur Sow}, doi = {10.1021/acs.nanolett.6b02111}, times_cited = {83}, issn = {1530-6984}, year = {2016}, date = {2016-09-01}, journal = {NANO LETTERS}, volume = {16}, number = {9}, pages = {5559-5567}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {We report a novel optical property in WS2 monolayer. The monolayer naturally exhibits beautiful in-plane periodical and lateral homojunctions by way of alternate dark and bright band in the fluorescence images of these monolayers. The interface between different fluorescence species within the sample is distinct and sharp. This gives rise to intriguing concentric triangular fluorescence patterns in the monolayer. The novel optical property of this special WS2 monolayer is facilitated by chemical heterogeneity. The photoluminescence of the bright band is dominated by emissions from trion and biexciton while the emission from defect-bound exciton dominates the photoluminescence at the dark band. The discovery of such concentric fluorescence patterns represents a potentially new form of optoelectronic or photonic functionality.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report a novel optical property in WS2 monolayer. The monolayer naturally exhibits beautiful in-plane periodical and lateral homojunctions by way of alternate dark and bright band in the fluorescence images of these monolayers. The interface between different fluorescence species within the sample is distinct and sharp. This gives rise to intriguing concentric triangular fluorescence patterns in the monolayer. The novel optical property of this special WS2 monolayer is facilitated by chemical heterogeneity. The photoluminescence of the bright band is dominated by emissions from trion and biexciton while the emission from defect-bound exciton dominates the photoluminescence at the dark band. The discovery of such concentric fluorescence patterns represents a potentially new form of optoelectronic or photonic functionality. |