Liu Wei
Position: Grad Students
Affiliation: NUS Graduate School for Integrative Sciences and Engineering
Research Type: Experiment
Email: a0095681@nus.edu.sg
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. |
Lin, Fanrong; Liu, Jiawei; Lu, Huan; Liu, Xin; Liu, Ying; Hu, Zhili; Lyu, Pin; Zhang, Zhuhua; Martin, Jens; Guo, Wanlin; Liu, Yanpeng Evolution of Graphene Dirac Fermions in Electric Double-Layer Transistors with a Soft Barrier Journal Article ADVANCED FUNCTIONAL MATERIALS, 2024, ISSN: 1616-301X. @article{ISI:001195156600001, title = {Evolution of Graphene Dirac Fermions in Electric Double-Layer Transistors with a Soft Barrier}, author = {Fanrong Lin and Jiawei Liu and Huan Lu and Xin Liu and Ying Liu and Zhili Hu and Pin Lyu and Zhuhua Zhang and Jens Martin and Wanlin Guo and Yanpeng Liu}, doi = {10.1002/adfm.202400553}, times_cited = {0}, issn = {1616-301X}, year = {2024}, date = {2024-04-02}, journal = {ADVANCED FUNCTIONAL MATERIALS}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {The interface and dielectric environment of graphene transistors are of great importance to commercial circuit integrations. The tangling bond in oxide-based dielectric severely lagged the carrier mobility while the 2D dielectric layer (for instance, hexagonal boron nitride) unavoidably hastened complicated condensed physics even at room temperature. Herein, multilayer black phosphorus (BP) a versatile and widely-tunable dielectric candidate for manifesting graphene fermions is demonstrated. Because of hetero-interfacial charge redistributions, a vertical electric double-layer between the bottom BP layer and top graphene spontaneously forms with the central BP layer as a soft barrier. Under dual-gate modulation, abnormal step-like evolution of Dirac fermions and charge-transfer quantum Hall effect arises while the intrinsic Dirac behavior of graphene is preserved, ascribing to the gate-tunable charge redistributions of dielectric BP layer. Moreover, the electric double-layer transistors apply equally well to bilayer graphene with similar Dirac behavior but an enhanced interfacial charge interference. The findings not only create a new avenue to manipulate the fermions by assembling graphene with narrow-gapped 2D layered materials but also promote electric double-layer transistors as a new build block to design multifunctional devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The interface and dielectric environment of graphene transistors are of great importance to commercial circuit integrations. The tangling bond in oxide-based dielectric severely lagged the carrier mobility while the 2D dielectric layer (for instance, hexagonal boron nitride) unavoidably hastened complicated condensed physics even at room temperature. Herein, multilayer black phosphorus (BP) a versatile and widely-tunable dielectric candidate for manifesting graphene fermions is demonstrated. Because of hetero-interfacial charge redistributions, a vertical electric double-layer between the bottom BP layer and top graphene spontaneously forms with the central BP layer as a soft barrier. Under dual-gate modulation, abnormal step-like evolution of Dirac fermions and charge-transfer quantum Hall effect arises while the intrinsic Dirac behavior of graphene is preserved, ascribing to the gate-tunable charge redistributions of dielectric BP layer. Moreover, the electric double-layer transistors apply equally well to bilayer graphene with similar Dirac behavior but an enhanced interfacial charge interference. The findings not only create a new avenue to manipulate the fermions by assembling graphene with narrow-gapped 2D layered materials but also promote electric double-layer transistors as a new build block to design multifunctional devices. |
Cording, Luke; Liu, Jiawei; Tan, Jun You; Watanabe, Kenji; Taniguchi, Takashi; Avsar, Ahmet; Ozyilmaz, Barbaros Highly anisotropic spin transport in ultrathin black phosphorus Journal Article NATURE MATERIALS, 23 (4), 2024, ISSN: 1476-1122. @article{ISI:001142010100002, title = {Highly anisotropic spin transport in ultrathin black phosphorus}, author = {Luke Cording and Jiawei Liu and Jun You Tan and Kenji Watanabe and Takashi Taniguchi and Ahmet Avsar and Barbaros Ozyilmaz}, doi = {10.1038/s41563-023-01779-8}, times_cited = {0}, issn = {1476-1122}, year = {2024}, date = {2024-01-12}, journal = {NATURE MATERIALS}, volume = {23}, number = {4}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {In anisotropic crystals, the direction-dependent effective mass of carriers can have a profound impact on spin transport dynamics. The puckered crystal structure of black phosphorus leads to direction-dependent charge transport and optical response, suggesting that it is an ideal system for studying anisotropic spin transport. To this end, we fabricate and characterize high-mobility encapsulated ultrathin black-phosphorus-based spin valves in a four-terminal geometry. Our measurements show that in-plane spin lifetimes are strongly gate tunable and exceed one nanosecond. Through high out-of-plane magnetic fields, we observe a fivefold enhancement in the out-of-plane spin signal case compared to in-plane and estimate a colossal spin-lifetime anisotropy of similar to 6. This finding is further confirmed by oblique Hanle measurements. Additionally, we estimate an in-plane spin-lifetime anisotropy ratio of up to 1.8. Our observation of strongly anisotropic spin transport along three orthogonal axes in this pristine material could be exploited to realize directionally tunable spin transport.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In anisotropic crystals, the direction-dependent effective mass of carriers can have a profound impact on spin transport dynamics. The puckered crystal structure of black phosphorus leads to direction-dependent charge transport and optical response, suggesting that it is an ideal system for studying anisotropic spin transport. To this end, we fabricate and characterize high-mobility encapsulated ultrathin black-phosphorus-based spin valves in a four-terminal geometry. Our measurements show that in-plane spin lifetimes are strongly gate tunable and exceed one nanosecond. Through high out-of-plane magnetic fields, we observe a fivefold enhancement in the out-of-plane spin signal case compared to in-plane and estimate a colossal spin-lifetime anisotropy of similar to 6. This finding is further confirmed by oblique Hanle measurements. Additionally, we estimate an in-plane spin-lifetime anisotropy ratio of up to 1.8. Our observation of strongly anisotropic spin transport along three orthogonal axes in this pristine material could be exploited to realize directionally tunable spin transport. |
2023 |
Lin, Fanrong; Cao, Zhonghan; Xiao, Feiping; Liu, Jiawei; Qiao, Jiabin; Xue, Minmin; Hu, Zhili; Liu, Ying; Lu, Huan; Zhang, Zhuhua; Martin, Jens; Tong, Qingjun; Guo, Wanlin; Liu, Yanpeng Graphene binding on black phosphorus enables high on/off ratios and mobility Journal Article NATIONAL SCIENCE REVIEW, 11 (2), 2023, ISSN: 2095-5138. @article{ISI:001121789900001, title = {Graphene binding on black phosphorus enables high on/off ratios and mobility}, author = {Fanrong Lin and Zhonghan Cao and Feiping Xiao and Jiawei Liu and Jiabin Qiao and Minmin Xue and Zhili Hu and Ying Liu and Huan Lu and Zhuhua Zhang and Jens Martin and Qingjun Tong and Wanlin Guo and Yanpeng Liu}, doi = {10.1093/nsr/nwad279}, times_cited = {0}, issn = {2095-5138}, year = {2023}, date = {2023-11-03}, journal = {NATIONAL SCIENCE REVIEW}, volume = {11}, number = {2}, publisher = {OXFORD UNIV PRESS}, address = {GREAT CLARENDON ST, OXFORD OX2 6DP, ENGLAND}, abstract = {Graphene is one of the most promising candidates for integrated circuits due to its robustness against short-channel effects, inherent high carrier mobility and desired gapless nature for Ohmic contact, but it is difficult to achieve satisfactory on/off ratios even at the expense of its carrier mobility, limiting its device applications. Here, we present a strategy to realize high back-gate switching ratios in a graphene monolayer with well-maintained high mobility by forming a vertical heterostructure with a black phosphorus multi-layer. By local current annealing, strain is introduced within an established area of the graphene, which forms a reflective interface with the rest of the strain-free area and thus generates a robust off-state via local current depletion. Applying a positive back-gate voltage to the heterostructure can keep the black phosphorus insulating, while a negative back-gate voltage changes the black phosphorus to be conductive because of hole accumulation. Then, a parallel channel is activated within the strain-free graphene area by edge-contacted electrodes, thereby largely inheriting the intrinsic carrier mobility of graphene in the on-state. As a result, the device can provide an on/off voltage ratio of >103 as well as a mobility of similar to 8000 cm(2) V-1 s(-1) at room temperature, meeting the low-power criterion suggested by the International Roadmap for Devices and Systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene is one of the most promising candidates for integrated circuits due to its robustness against short-channel effects, inherent high carrier mobility and desired gapless nature for Ohmic contact, but it is difficult to achieve satisfactory on/off ratios even at the expense of its carrier mobility, limiting its device applications. Here, we present a strategy to realize high back-gate switching ratios in a graphene monolayer with well-maintained high mobility by forming a vertical heterostructure with a black phosphorus multi-layer. By local current annealing, strain is introduced within an established area of the graphene, which forms a reflective interface with the rest of the strain-free area and thus generates a robust off-state via local current depletion. Applying a positive back-gate voltage to the heterostructure can keep the black phosphorus insulating, while a negative back-gate voltage changes the black phosphorus to be conductive because of hole accumulation. Then, a parallel channel is activated within the strain-free graphene area by edge-contacted electrodes, thereby largely inheriting the intrinsic carrier mobility of graphene in the on-state. As a result, the device can provide an on/off voltage ratio of >103 as well as a mobility of similar to 8000 cm(2) V-1 s(-1) at room temperature, meeting the low-power criterion suggested by the International Roadmap for Devices and Systems. |
2022 |
Huang, Zeping; Song, Xuan; Chen, Yaoyao; Yang, Han; Yuan, Peiwen; Ma, Hang; Qiao, Jingsi; Zhang, Yu; Sun, Jiatao; Zhang, Teng; Huang, Yuan; Liu, Liwei; Gao, Hong-Jun; Wang, Yeliang Size Dependence of Charge-Density-Wave Orders in Single-Layer NbSe2 Hetero/Homophase Junctions Journal Article JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 13 (8), pp. 1901-1907, 2022, ISSN: 1948-7185. @article{ISI:000766749900002, title = {Size Dependence of Charge-Density-Wave Orders in Single-Layer NbSe_{2} Hetero/Homophase Junctions}, author = {Zeping Huang and Xuan Song and Yaoyao Chen and Han Yang and Peiwen Yuan and Hang Ma and Jingsi Qiao and Yu Zhang and Jiatao Sun and Teng Zhang and Yuan Huang and Liwei Liu and Hong-Jun Gao and Yeliang Wang}, doi = {10.1021/acs.jpclett.1c04138}, times_cited = {0}, issn = {1948-7185}, year = {2022}, date = {2022-03-03}, journal = {JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, volume = {13}, number = {8}, pages = {1901-1907}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Controlling charge-density-wave (CDW) orders in two-dimensional (2D) crystals has attracted a great deal of interest because of their fundamental physics and their demand inse in miniaturized devices. In this work, we systematically studied the size-dependent CDW orders in single-layer hetero/homo-NbSe2 stacking junctions. We found that the CDW orders in the top 1T-NbSe2 layer of the junctions are highly dependent on its lateral size. For the 1T/2H-NbSe2 heterojunction, the critical lateral size of 1T-NbSe2 islands for the formation of well-defined CDW orders is similar to 26 nm, whereas below 15 nm, the CDW orders melt. However, for the 1T/1T-NbSe2 homojunction, the CDW orders in the islands can persist even with a lateral size of <11 nm. Our findings illuminate the fresh phenomenon of size-dependent CDW orders existing in 2D van der Waals hetero/homojunctions and provide useful information for the control of CDW orders.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Controlling charge-density-wave (CDW) orders in two-dimensional (2D) crystals has attracted a great deal of interest because of their fundamental physics and their demand inse in miniaturized devices. In this work, we systematically studied the size-dependent CDW orders in single-layer hetero/homo-NbSe2 stacking junctions. We found that the CDW orders in the top 1T-NbSe2 layer of the junctions are highly dependent on its lateral size. For the 1T/2H-NbSe2 heterojunction, the critical lateral size of 1T-NbSe2 islands for the formation of well-defined CDW orders is similar to 26 nm, whereas below 15 nm, the CDW orders melt. However, for the 1T/1T-NbSe2 homojunction, the CDW orders in the islands can persist even with a lateral size of <11 nm. Our findings illuminate the fresh phenomenon of size-dependent CDW orders existing in 2D van der Waals hetero/homojunctions and provide useful information for the control of CDW orders. |
Liu, Hongwei; Mendelson, Noah; Abidi, Irfan H; Li, Shaobo; Liu, Zhenjing; Cai, Yuting; Zhang, Kenan; You, Jiawen; Tamtaji, Mohsen; Wong, Hoilun; Ding, Yao; Chen, Guojie; Aharonovich, Igor; Luo, Zhengtang Rational Control on Quantum Emitter Formation in Carbon-Doped Monolayer Hexagonal Boron Nitride Journal Article ACS APPLIED MATERIALS & INTERFACES , 14 (2), pp. 3189-3198, 2022, ISSN: 1944-8244. @article{ISI:000768619500071, title = {Rational Control on Quantum Emitter Formation in Carbon-Doped Monolayer Hexagonal Boron Nitride }, author = {Hongwei Liu and Noah Mendelson and Irfan H Abidi and Shaobo Li and Zhenjing Liu and Yuting Cai and Kenan Zhang and Jiawen You and Mohsen Tamtaji and Hoilun Wong and Yao Ding and Guojie Chen and Igor Aharonovich and Zhengtang Luo}, doi = {10.1021/acsami.1c21781}, times_cited = {0}, issn = {1944-8244}, year = {2022}, date = {2022-01-19}, journal = {ACS APPLIED MATERIALS & INTERFACES }, volume = {14}, number = {2}, pages = {3189-3198}, publisher = {AMER CHEMICAL SOC }, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA }, abstract = {Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising candidates for quantum light generation. Despite this, techniques to control the formation of hBN SPEs down to the monolayer limit are yet to be demonstrated. Recent experimental and theoretical investigations have suggested that the visible wavelength single-photon emitters in hBN originate from carbon-related defects. Here, we demonstrate a simple strategy for controlling SPE creation during the chemical vapor deposition growth of monolayer hBN via regulating surface carbon concentration. By increasing the surface carbon concentration during hBN growth, we observe increases in carbon doping levels by 2.4-fold for B-C bonds and 1.6-fold for N-C bonds. For the same samples, we observe an increase in the SPE density from 0.13 to 0.30 emitters/mu m(2). Our simple method enables the reliable creation of hBN SPEs in monolayer samples for the first time, opening the door to advanced two-dimensional (2D) quantum state engineering. }, keywords = {}, pubstate = {published}, tppubtype = {article} } Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising candidates for quantum light generation. Despite this, techniques to control the formation of hBN SPEs down to the monolayer limit are yet to be demonstrated. Recent experimental and theoretical investigations have suggested that the visible wavelength single-photon emitters in hBN originate from carbon-related defects. Here, we demonstrate a simple strategy for controlling SPE creation during the chemical vapor deposition growth of monolayer hBN via regulating surface carbon concentration. By increasing the surface carbon concentration during hBN growth, we observe increases in carbon doping levels by 2.4-fold for B-C bonds and 1.6-fold for N-C bonds. For the same samples, we observe an increase in the SPE density from 0.13 to 0.30 emitters/mu m(2). Our simple method enables the reliable creation of hBN SPEs in monolayer samples for the first time, opening the door to advanced two-dimensional (2D) quantum state engineering. |
Liu, Hongwei; Mendelson, Noah; Abidi, Irfan H; Li, Shaobo; Liu, Zhenjing; Cai, Yuting; Zhang, Kenan; You, Jiawen; Tamtaji, Mohsen; Wong, Hoilun; Ding, Yao; Chen, Guojie; Aharonovich, Igor; Luo, Zhengtang Rational Control on Quantum Emitter Formation in Carbon-Doped Monolayer Hexagonal Boron Nitride Journal Article ACS APPLIED MATERIALS & INTERFACES, 14 (2), pp. 3189-3198, 2022, ISSN: 1944-8244. @article{ISI:000742236200001, title = {Rational Control on Quantum Emitter Formation in Carbon-Doped Monolayer Hexagonal Boron Nitride}, author = {Hongwei Liu and Noah Mendelson and Irfan H Abidi and Shaobo Li and Zhenjing Liu and Yuting Cai and Kenan Zhang and Jiawen You and Mohsen Tamtaji and Hoilun Wong and Yao Ding and Guojie Chen and Igor Aharonovich and Zhengtang Luo}, doi = {10.1021/acsami.1c21781}, times_cited = {0}, issn = {1944-8244}, year = {2022}, date = {2022-01-06}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {14}, number = {2}, pages = {3189-3198}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising candidates for quantum light generation. Despite this, techniques to control the formation of hBN SPEs down to the monolayer limit are yet to be demonstrated. Recent experimental and theoretical investigations have suggested that the visible wavelength single-photon emitters in hBN originate from carbon-related defects. Here, we demonstrate a simple strategy for controlling SPE creation during the chemical vapor deposition growth of monolayer hBN via regulating surface carbon concentration. By increasing the surface carbon concentration during hBN growth, we observe increases in carbon doping levels by 2.4-fold for B-C bonds and 1.6-fold for N-C bonds. For the same samples, we observe an increase in the SPE density from 0.13 to 0.30 emitters/mu m(2). Our simple method enables the reliable creation of hBN SPEs in monolayer samples for the first time, opening the door to advanced two-dimensional (2D) quantum state engineering.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Single-photon emitters (SPEs) in hexagonal boron nitride (hBN) are promising candidates for quantum light generation. Despite this, techniques to control the formation of hBN SPEs down to the monolayer limit are yet to be demonstrated. Recent experimental and theoretical investigations have suggested that the visible wavelength single-photon emitters in hBN originate from carbon-related defects. Here, we demonstrate a simple strategy for controlling SPE creation during the chemical vapor deposition growth of monolayer hBN via regulating surface carbon concentration. By increasing the surface carbon concentration during hBN growth, we observe increases in carbon doping levels by 2.4-fold for B-C bonds and 1.6-fold for N-C bonds. For the same samples, we observe an increase in the SPE density from 0.13 to 0.30 emitters/mu m(2). Our simple method enables the reliable creation of hBN SPEs in monolayer samples for the first time, opening the door to advanced two-dimensional (2D) quantum state engineering. |
Liu, Hongwei; He, Wanzhen; Liu, Zhenjing; Abidi, Irfan H; Ding, Yao; Galligan, Patrick Ryan; Tamtaji, Mohsen; Li, Jingwei; Cai, Yuting; Kang, Ting; Wong, Hoilun; Li, Zhongjian; Zhao, Pei; Gao, Zhaoli; Mi, Yongli; Xu, Zhiping; Luo, Zhengtang Structure evolution of hBN grown on molten Cu by regulating precursor flux during chemical vapor deposition Journal Article 2D MATERIALS, 9 (1), 2022, ISSN: 2053-1583. @article{ISI:000710695900001, title = {Structure evolution of hBN grown on molten Cu by regulating precursor flux during chemical vapor deposition}, author = {Hongwei Liu and Wanzhen He and Zhenjing Liu and Irfan H Abidi and Yao Ding and Patrick Ryan Galligan and Mohsen Tamtaji and Jingwei Li and Yuting Cai and Ting Kang and Hoilun Wong and Zhongjian Li and Pei Zhao and Zhaoli Gao and Yongli Mi and Zhiping Xu and Zhengtang Luo}, doi = {10.1088/2053-1583/ac2e59}, times_cited = {0}, issn = {2053-1583}, year = {2022}, date = {2022-01-01}, journal = {2D MATERIALS}, volume = {9}, number = {1}, publisher = {IOP Publishing Ltd}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {We demonstrate the structure evolution of hexagonal boron nitride (hBN) flakes grown on molten Cu in atmospheric pressure chemical vapor deposition by regulating the flux of precursor. We found that under lower precursor flux, tuned by temperature that controls the sublimation rates, the hBN grains change from triangle to truncated triangle shape with additional B-terminated edges, which could be understood through kinetic Wulff construction, while under higher flux, they form circular shape following deposition-controlled growth and predicted by a phase field modeling. In addition to the monolayer morphology from a single nucleation, adlayer patterns with centered aggregation and diffusive features at high precursor flux are observed and simulated by a two-dimensional (2D) diffusion-reaction model, where the random diffusion and deposition are revealed to be the dominating kinetics. The nucleation density and growth velocity could also be modulated by the ammonia borane heating temperature, where 80 degrees C is found to be optimal for the largest hBN grain size. Our transmission electron microscopy study shows that a misalignment of coalescing grains occurs on such molten Cu substrate, deviated from those observed on molten Au. Our results provide a new tool for the shape and grain size control of 2D materials and the understanding of their growth kinetics for large scale production.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We demonstrate the structure evolution of hexagonal boron nitride (hBN) flakes grown on molten Cu in atmospheric pressure chemical vapor deposition by regulating the flux of precursor. We found that under lower precursor flux, tuned by temperature that controls the sublimation rates, the hBN grains change from triangle to truncated triangle shape with additional B-terminated edges, which could be understood through kinetic Wulff construction, while under higher flux, they form circular shape following deposition-controlled growth and predicted by a phase field modeling. In addition to the monolayer morphology from a single nucleation, adlayer patterns with centered aggregation and diffusive features at high precursor flux are observed and simulated by a two-dimensional (2D) diffusion-reaction model, where the random diffusion and deposition are revealed to be the dominating kinetics. The nucleation density and growth velocity could also be modulated by the ammonia borane heating temperature, where 80 degrees C is found to be optimal for the largest hBN grain size. Our transmission electron microscopy study shows that a misalignment of coalescing grains occurs on such molten Cu substrate, deviated from those observed on molten Au. Our results provide a new tool for the shape and grain size control of 2D materials and the understanding of their growth kinetics for large scale production. |
2021 |
Reddy, Vundrala Sumedha; Tian, Yilong; Zhang, Chuanqi; Ye, Zhen; Roy, Kallol; Chinnappan, Amutha; Ramakrishna, Seeram; Liu, Wei; Ghosh, Rituparna A Review on Electrospun Nanofibers Based Advanced Applications: From Health Care to Energy Devices Journal Article POLYMERS, 13 (21), 2021. @article{ISI:000719048500001, title = {A Review on Electrospun Nanofibers Based Advanced Applications: From Health Care to Energy Devices}, author = {Vundrala Sumedha Reddy and Yilong Tian and Chuanqi Zhang and Zhen Ye and Kallol Roy and Amutha Chinnappan and Seeram Ramakrishna and Wei Liu and Rituparna Ghosh}, doi = {10.3390/polym13213746}, times_cited = {0}, year = {2021}, date = {2021-11-01}, journal = {POLYMERS}, volume = {13}, number = {21}, publisher = {MDPI}, address = {ST ALBAN-ANLAGE 66, CH-4052 BASEL, SWITZERLAND}, abstract = {Electrospun nanofibers have been exploited in multidisciplinary fields with numerous applications for decades. Owing to their interconnected ultrafine fibrous structure, high surface-to-volume ratio, tortuosity, permeability, and miniaturization ability along with the benefits of their lightweight, porous nanofibrous structure, they have been extensively utilized in various research fields for decades. Electrospun nanofiber technologies have paved unprecedented advancements with new innovations and discoveries in several fields of application including energy devices and biomedical and environmental appliances. This review article focused on providing a comprehensive overview related to the recent advancements in health care and energy devices while emphasizing on the importance and uniqueness of utilizing nanofibers. A brief description regarding the effect of electrospinning techniques, setup modifications, and parameters optimization on the nanofiber morphology was also provided. The article is concluded with a short discussion on current research challenges and future perspectives.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electrospun nanofibers have been exploited in multidisciplinary fields with numerous applications for decades. Owing to their interconnected ultrafine fibrous structure, high surface-to-volume ratio, tortuosity, permeability, and miniaturization ability along with the benefits of their lightweight, porous nanofibrous structure, they have been extensively utilized in various research fields for decades. Electrospun nanofiber technologies have paved unprecedented advancements with new innovations and discoveries in several fields of application including energy devices and biomedical and environmental appliances. This review article focused on providing a comprehensive overview related to the recent advancements in health care and energy devices while emphasizing on the importance and uniqueness of utilizing nanofibers. A brief description regarding the effect of electrospinning techniques, setup modifications, and parameters optimization on the nanofiber morphology was also provided. The article is concluded with a short discussion on current research challenges and future perspectives. |
2020 |
Wang, Dingguan; Wang, Zishen; Liu, Wei; Arramel, ; Zhou, Jun; Feng, Yuan Ping; Loh, Kian Ping; Wu, Jishan; Wee, Andrew T S Atomic-Level Electronic Properties of Carbon Nitride Monolayers Journal Article ACS NANO, 14 (10), pp. 14008-14016, 2020, ISSN: 1936-0851. @article{ISI:000586793400147, title = {Atomic-Level Electronic Properties of Carbon Nitride Monolayers}, author = {Dingguan Wang and Zishen Wang and Wei Liu and Arramel and Jun Zhou and Yuan Ping Feng and Kian Ping Loh and Jishan Wu and Andrew T S Wee}, doi = {10.1021/acsnano.0c06535}, times_cited = {0}, issn = {1936-0851}, year = {2020}, date = {2020-10-27}, journal = {ACS NANO}, volume = {14}, number = {10}, pages = {14008-14016}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Heteroatom-doped carbon-based materials are of significance for clean energy conversion and storage because of their fascinating electronic properties, low cost, high durability, and environmental friendliness. Atomically precise fabrication of carbon-based materials with well-defined heteroatom-dopant positions and atomic-scale understanding of their atomic-level electronic properties is a challenge. Herein, we demonstrate the bottom-up on-surface synthesis of 1D and 2D monolayer carbon nitride nanostructures with precise control of the nitrogen-atom doping sites and pore sizes. We also observe an electronic band offset at the C-N heterojunction. Using high-resolution scanning tunneling microscopy, the atomic structure of the as-prepared carbon nitride nanoporous monolayers are revealed, indicating successful and precise control of the structures and N atom doping sites. Furthermore, corroborated by theoretical calculations, scanning tunneling spectroscopy measurements reveal a valence band shift of 140 meV that results in an electric field of 2.9 x 10(8) V m(-1) at the C-N heterojunction, indicating efficient separation of the electron-hole pair at the N doping site. Our finding offers direct atomic-level insights into the local electronic structure of the heteroatom-doped carbon-based materials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Heteroatom-doped carbon-based materials are of significance for clean energy conversion and storage because of their fascinating electronic properties, low cost, high durability, and environmental friendliness. Atomically precise fabrication of carbon-based materials with well-defined heteroatom-dopant positions and atomic-scale understanding of their atomic-level electronic properties is a challenge. Herein, we demonstrate the bottom-up on-surface synthesis of 1D and 2D monolayer carbon nitride nanostructures with precise control of the nitrogen-atom doping sites and pore sizes. We also observe an electronic band offset at the C-N heterojunction. Using high-resolution scanning tunneling microscopy, the atomic structure of the as-prepared carbon nitride nanoporous monolayers are revealed, indicating successful and precise control of the structures and N atom doping sites. Furthermore, corroborated by theoretical calculations, scanning tunneling spectroscopy measurements reveal a valence band shift of 140 meV that results in an electric field of 2.9 x 10(8) V m(-1) at the C-N heterojunction, indicating efficient separation of the electron-hole pair at the N doping site. Our finding offers direct atomic-level insights into the local electronic structure of the heteroatom-doped carbon-based materials. |
Qian, Cheng; Zhou, Weiqiang; Qiao, Jingsi; Wang, Dongdong; Li, Xing; Teo, Wei Liang; Shi, Xiangyan; Wu, Hongwei; Di, Jun; Wang, Hou; Liu, Guofeng; Gu, Long; Liu, Jiawei; Feng, Lili; Liu, Yuchuan; Quek, Su Ying; Loh, Kian Ping; Zhao, Yanli JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 142 (42), pp. 18138-18149, 2020, ISSN: 0002-7863. @article{ISI:000580559000038, title = {Linkage Engineering by Harnessing Supramolecular Interactions to Fabricate 2D Hydrazone-Linked Covalent Organic Framework Platforms toward Advanced Catalysis}, author = {Cheng Qian and Weiqiang Zhou and Jingsi Qiao and Dongdong Wang and Xing Li and Wei Liang Teo and Xiangyan Shi and Hongwei Wu and Jun Di and Hou Wang and Guofeng Liu and Long Gu and Jiawei Liu and Lili Feng and Yuchuan Liu and Su Ying Quek and Kian Ping Loh and Yanli Zhao}, doi = {10.1021/jacs.0c08436}, times_cited = {0}, issn = {0002-7863}, year = {2020}, date = {2020-10-21}, journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, volume = {142}, number = {42}, pages = {18138-18149}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with tailor-made structures and functionalities. To facilitate their utilization for advanced applications, it is crucial to develop a systematic approach to control the properties of COFs, including the crystallinity, stability, and functionalities. However, such an integrated design is challenging to achieve. Herein, we report supramolecular strategy-based linkage engineering to fabricate a versatile 2D hydrazone-linked COF platform for the coordination of different transition metal ions. Intra- and intermolecular hydrogen bonding as well as electrostatic interactions in the antiparallel stacking mode were first utilized to obtain two isoreticular COFs, namely COF-DB and COF-DT. On account of suitable nitrogen sites in COF-DB, the further metalation of COF-DB was accomplished upon the complexation with seven divalent transition metal ions M(II) (M = Mn, Co, Ni, Cu, Zn, Pd, and Cd) under mild conditions. The resultant M/COF-DB exhibited extended p-conjugation, improved crystallinity, enhanced stability, and additional functionalities as compared to the parent COF-DB. Furthermore, the dynamic nature of the coordination bonding in M/COF-DB allows for the easy replacement of metal ions through a postsynthetic exchange. In particular, the coordination mode in Pd/COF-DB endows it with excellent catalytic activity and cyclic stability as a heterogeneous catalyst for the Suzuki-Miyaura cross-coupling reaction, outperforming its amorphous counterparts and Pd/COF-DT. This strategy provides an opportunity for the construction of 2D COFs with designable functions and opens an avenue to create COFs as multifunctional systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with tailor-made structures and functionalities. To facilitate their utilization for advanced applications, it is crucial to develop a systematic approach to control the properties of COFs, including the crystallinity, stability, and functionalities. However, such an integrated design is challenging to achieve. Herein, we report supramolecular strategy-based linkage engineering to fabricate a versatile 2D hydrazone-linked COF platform for the coordination of different transition metal ions. Intra- and intermolecular hydrogen bonding as well as electrostatic interactions in the antiparallel stacking mode were first utilized to obtain two isoreticular COFs, namely COF-DB and COF-DT. On account of suitable nitrogen sites in COF-DB, the further metalation of COF-DB was accomplished upon the complexation with seven divalent transition metal ions M(II) (M = Mn, Co, Ni, Cu, Zn, Pd, and Cd) under mild conditions. The resultant M/COF-DB exhibited extended p-conjugation, improved crystallinity, enhanced stability, and additional functionalities as compared to the parent COF-DB. Furthermore, the dynamic nature of the coordination bonding in M/COF-DB allows for the easy replacement of metal ions through a postsynthetic exchange. In particular, the coordination mode in Pd/COF-DB endows it with excellent catalytic activity and cyclic stability as a heterogeneous catalyst for the Suzuki-Miyaura cross-coupling reaction, outperforming its amorphous counterparts and Pd/COF-DT. This strategy provides an opportunity for the construction of 2D COFs with designable functions and opens an avenue to create COFs as multifunctional systems. |
Lin, Fanrong; Qiao, Jiabin; Huang, Junye; Liu, Jiawei; Fu, Deyi; Mayorov, Alexander S; Chen, Hao; Mukherjee, Paromita; Qu, Tingyu; Sow, Chorng-Haur; Watanabe, Kenji; Taniguchi, Takashi; Ozyilmaz, Barbaros Heteromoire Engineering on Magnetic Bloch Transport in Twisted Graphene Superlattices Journal Article NANO LETTERS, 20 (10), pp. 7572-7579, 2020, ISSN: 1530-6984. @article{ISI:000613073900006, title = {Heteromoire Engineering on Magnetic Bloch Transport in Twisted Graphene Superlattices}, author = {Fanrong Lin and Jiabin Qiao and Junye Huang and Jiawei Liu and Deyi Fu and Alexander S Mayorov and Hao Chen and Paromita Mukherjee and Tingyu Qu and Chorng-Haur Sow and Kenji Watanabe and Takashi Taniguchi and Barbaros Ozyilmaz}, doi = {10.1021/acs.nanolett.0c03062}, times_cited = {0}, issn = {1530-6984}, year = {2020}, date = {2020-10-14}, journal = {NANO LETTERS}, volume = {20}, number = {10}, pages = {7572-7579}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Localized electrons subject to applied magnetic fields can restart to propagate freely through the lattice in delocalized magnetic Bloch states (MBSs) when the lattice periodicity is commensurate with the magnetic length. Twisted graphene superlattices with moire wavelength tunability enable experimental access to the unique delocalization in a controllable fashion. Here, we report the observation and characterization of high-temperature Brown-Zak (BZ) oscillations which come in two types, 1/B and B periodicity, originating from the generation of integer and fractional MBSs, in the twisted bilayer and trilayer graphene superlattices, respectively. Coexisting periodic-in-1/B oscillations assigned to different moire wavelengths are dramatically observed in small-angle twisted bilayer graphene, which may arise from angledisorder-induced in-plane heteromoire superlattices. Moreover, the vertical stacking of heteromoire supercells in double-twisted trilayer graphene results in a mega-sized superlattice. The exotic superlattice contributes to the periodic-in-B oscillation and dominates the magnetic Bloch transport.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Localized electrons subject to applied magnetic fields can restart to propagate freely through the lattice in delocalized magnetic Bloch states (MBSs) when the lattice periodicity is commensurate with the magnetic length. Twisted graphene superlattices with moire wavelength tunability enable experimental access to the unique delocalization in a controllable fashion. Here, we report the observation and characterization of high-temperature Brown-Zak (BZ) oscillations which come in two types, 1/B and B periodicity, originating from the generation of integer and fractional MBSs, in the twisted bilayer and trilayer graphene superlattices, respectively. Coexisting periodic-in-1/B oscillations assigned to different moire wavelengths are dramatically observed in small-angle twisted bilayer graphene, which may arise from angledisorder-induced in-plane heteromoire superlattices. Moreover, the vertical stacking of heteromoire supercells in double-twisted trilayer graphene results in a mega-sized superlattice. The exotic superlattice contributes to the periodic-in-B oscillation and dominates the magnetic Bloch transport. |
Zeng, Shengwei; Tang, Chi Sin; Yin, Xinmao; Li, Changjian; Li, Mengsha; Huang, Zhen; Hu, Junxiong; Liu, Wei; Omar, Ganesh Ji; Jani, Hariom; Lim, Zhi Shiuh; Han, Kun; Wan, Dongyang; Yang, Ping; Pennycook, Stephen John; Wee, Andrew T S; Ariando, Ariando Phase Diagram and Superconducting Dome of Infinite-Layer Nd1-xSxNiO2 Thin Films Journal Article PHYSICAL REVIEW LETTERS, 125 (14), 2020, ISSN: 0031-9007. @article{ISI:000574781200009, title = {Phase Diagram and Superconducting Dome of Infinite-Layer Nd_{1-\textit{x}}S\textit{_{x}}NiO_{2} Thin Films}, author = {Shengwei Zeng and Chi Sin Tang and Xinmao Yin and Changjian Li and Mengsha Li and Zhen Huang and Junxiong Hu and Wei Liu and Ganesh Ji Omar and Hariom Jani and Zhi Shiuh Lim and Kun Han and Dongyang Wan and Ping Yang and Stephen John Pennycook and Andrew T S Wee and Ariando Ariando}, doi = {10.1103/PhysRevLett.125.147003}, times_cited = {0}, issn = {0031-9007}, year = {2020}, date = {2020-10-02}, journal = {PHYSICAL REVIEW LETTERS}, volume = {125}, number = {14}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Infinite-layer Nd1-xSxNiO2 thin films with Sr doping level x from 0.08 to 0.3 are synthesized and investigated. We find a superconducting dome x between 0.12 and 0.235 accompanied by a weakly insulating behavior in both under- and overdoped regimes. The dome is akin to that in the electron-doped 214-type and infinite-layer cuprate superconductors. For x >= 0.18, the normal state Hall coefficient (RH) changes the sign from negative to positive as the temperature decreases. The temperature of the sign changes decreases monotonically with decreasing x from the overdoped side and approaches the superconducting dome at the midpoint, suggesting a reconstruction of the Fermi surface with the dopant concentration across the dome.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Infinite-layer Nd1-xSxNiO2 thin films with Sr doping level x from 0.08 to 0.3 are synthesized and investigated. We find a superconducting dome x between 0.12 and 0.235 accompanied by a weakly insulating behavior in both under- and overdoped regimes. The dome is akin to that in the electron-doped 214-type and infinite-layer cuprate superconductors. For x >= 0.18, the normal state Hall coefficient (RH) changes the sign from negative to positive as the temperature decreases. The temperature of the sign changes decreases monotonically with decreasing x from the overdoped side and approaches the superconducting dome at the midpoint, suggesting a reconstruction of the Fermi surface with the dopant concentration across the dome. |
Yao, Chuanhao; Guo, Na; Xi, Shibo; Xu, Cong-Qiao; Liu, Wei; Zhao, Xiaoxu; Li, Jing; Fang, Hanyan; Su, Jie; Chen, Zhongxin; Yan, Huan; Qiu, Zhizhan; Lyu, Pin; Chen, Cheng; Xu, Haomin; Peng, Xinnan; Li, Xinzhe; Liu, Bin; Su, Chenliang; Pennycook, Stephen J; Sun, Cheng-Jun; Li, Jun; Zhang, Chun; Du, Yonghua; Lu, Jiong Atomically-precise dopant-controlled single cluster catalysis for electrochemical nitrogen reduction Journal Article NATURE COMMUNICATIONS, 11 (1), 2020, ISSN: 2041-1723. @article{ISI:000569891500016, title = {Atomically-precise dopant-controlled single cluster catalysis for electrochemical nitrogen reduction}, author = {Chuanhao Yao and Na Guo and Shibo Xi and Cong-Qiao Xu and Wei Liu and Xiaoxu Zhao and Jing Li and Hanyan Fang and Jie Su and Zhongxin Chen and Huan Yan and Zhizhan Qiu and Pin Lyu and Cheng Chen and Haomin Xu and Xinnan Peng and Xinzhe Li and Bin Liu and Chenliang Su and Stephen J Pennycook and Cheng-Jun Sun and Jun Li and Chun Zhang and Yonghua Du and Jiong Lu}, doi = {10.1038/s41467-020-18080-w}, times_cited = {0}, issn = {2041-1723}, year = {2020}, date = {2020-09-01}, journal = {NATURE COMMUNICATIONS}, volume = {11}, number = {1}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {The ability to precisely engineer the doping of sub-nanometer bimetallic clusters offers exciting opportunities for tailoring their catalytic performance with atomic accuracy. However, the fabrication of singly dispersed bimetallic cluster catalysts with atomic-level control of dopants has been a long-standing challenge. Herein, we report a strategy for the controllable synthesis of a precisely doped single cluster catalyst consisting of partially ligand-enveloped Au4Pt2 clusters supported on defective graphene. This creates a bimetal single cluster catalyst (Au4Pt2/G) with exceptional activity for electrochemical nitrogen (N-2) reduction. Our mechanistic study reveals that each N-2 molecule is activated in the confined region between cluster and graphene. The heteroatom dopant plays an indispensable role in the activation of N-2 via an enhanced back donation of electrons to the N-2 LUMO. Moreover, besides the heteroatom Pt, the catalytic performance of single cluster catalyst can be further tuned by using Pd in place of Pt as the dopant. The fabrication of singly dispersed metal cluster catalysts with atomic-level control of dopants is a long-standing challenge. Here, the authors report a strategy for the synthesis of a precisely doped single cluster catalyst which shows exceptional activity for electrochemical dinitrogen reduction.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The ability to precisely engineer the doping of sub-nanometer bimetallic clusters offers exciting opportunities for tailoring their catalytic performance with atomic accuracy. However, the fabrication of singly dispersed bimetallic cluster catalysts with atomic-level control of dopants has been a long-standing challenge. Herein, we report a strategy for the controllable synthesis of a precisely doped single cluster catalyst consisting of partially ligand-enveloped Au4Pt2 clusters supported on defective graphene. This creates a bimetal single cluster catalyst (Au4Pt2/G) with exceptional activity for electrochemical nitrogen (N-2) reduction. Our mechanistic study reveals that each N-2 molecule is activated in the confined region between cluster and graphene. The heteroatom dopant plays an indispensable role in the activation of N-2 via an enhanced back donation of electrons to the N-2 LUMO. Moreover, besides the heteroatom Pt, the catalytic performance of single cluster catalyst can be further tuned by using Pd in place of Pt as the dopant. The fabrication of singly dispersed metal cluster catalysts with atomic-level control of dopants is a long-standing challenge. Here, the authors report a strategy for the synthesis of a precisely doped single cluster catalyst which shows exceptional activity for electrochemical dinitrogen reduction. |
Xu, Zai-Quan; Mendelson, Noah; Scott, John A; Li, Chi; Abidi, Irfan H; Liu, Hongwei; Luo, Zhengtang; Aharonovich, Igor; Toth, Milos Charge and energy transfer of quantum emitters in 2D heterostructures Journal Article 2D MATERIALS, 7 (3), 2020, ISSN: 2053-1583. @article{ISI:000528570100001, title = {Charge and energy transfer of quantum emitters in 2D heterostructures}, author = {Zai-Quan Xu and Noah Mendelson and John A Scott and Chi Li and Irfan H Abidi and Hongwei Liu and Zhengtang Luo and Igor Aharonovich and Milos Toth}, doi = {10.1088/2053-1583/ab7fc3}, times_cited = {1}, issn = {2053-1583}, year = {2020}, date = {2020-07-01}, journal = {2D MATERIALS}, volume = {7}, number = {3}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {Graphene is often used as an acceptor in highly efficient energy transfer processes between its electrons and neighbouring optical emitters such as quantum dots, fluorescent molecules and color centres in crystals. Here we demonstrate that graphene can act not only as an acceptor in energy transfer processes, but also an acceptor of charge donated by photoexcited quantum emitters. Specifically, we use heterostructures comprised of graphene and hexagonal boron nitride (hBN) to demonstrate a reversible charge transfer process from quantum emitters in hBN to graphene. The process acts as a controllable, energy-resolved filter that quenches quantum emitters with ground states located above the Fermi level of graphene. Our findings shed light on the positions of hBN defect states within the bandgap of hBN, and are important for the design of devices based on 2D heterostructures, opening new avenues to technologies based on electrical excitation, manipulation, and readout of the quantum states of optical emitters.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene is often used as an acceptor in highly efficient energy transfer processes between its electrons and neighbouring optical emitters such as quantum dots, fluorescent molecules and color centres in crystals. Here we demonstrate that graphene can act not only as an acceptor in energy transfer processes, but also an acceptor of charge donated by photoexcited quantum emitters. Specifically, we use heterostructures comprised of graphene and hexagonal boron nitride (hBN) to demonstrate a reversible charge transfer process from quantum emitters in hBN to graphene. The process acts as a controllable, energy-resolved filter that quenches quantum emitters with ground states located above the Fermi level of graphene. Our findings shed light on the positions of hBN defect states within the bandgap of hBN, and are important for the design of devices based on 2D heterostructures, opening new avenues to technologies based on electrical excitation, manipulation, and readout of the quantum states of optical emitters. |