Cheng Lin Quan Nicholas
Group: Prof Quek Su Ying
CA2DM Publications:
2025 |
Cheng, Nicholas Lin Quan; Ulman, Kanchan Ajit; Quek, Su Ying Defect Engineering in Hexagonal Boron Nitride: Optical Properties of Stable Defect Complexes Arising from Boron Interstitials Journal Article ACS APPLIED MATERIALS & INTERFACES, 17 (16), pp. 24058-24070, 2025, ISSN: 1944-8244. @article{ISI:001466592300001, title = {Defect Engineering in Hexagonal Boron Nitride: Optical Properties of Stable Defect Complexes Arising from Boron Interstitials}, author = {Nicholas Lin Quan Cheng and Kanchan Ajit Ulman and Su Ying Quek}, doi = {10.1021/acsami.4c19034}, times_cited = {0}, issn = {1944-8244}, year = {2025}, date = {2025-04-14}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {17}, number = {16}, pages = {24058-24070}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor that is promising as a host material for solid-state quantum technologies through defect engineering. It has been shown that boron atoms can be removed from the lattice upon irradiation by electrons or light ions, creating boron vacancies and boron interstitials. While the optical properties of boron-vacancy-derived defects have been studied extensively, little is known about the optical properties of boron-interstitial-derived defects. In this work, we use state-of-the-art first-principles calculations to predict the electronic and optical properties of boron interstitials (Bint) and defect complexes comprising Bint and substitutional carbon impurities at boron and nitrogen sites (CB and CN). These carbon impurities can be present in as-grown hBN and can also be introduced intentionally. We demonstrate that these complexes are expected to be stable at room temperature. Our GW-Bethe-Salpeter equation (BSE) calculations show that Bint-CB and Bint-CN have low-energy optical transitions that are isolated in energy, making them suitable as single-photon emitters. Together with constrained density functional theory calculations to capture the red shift due to emission, we predict that Bint-CB and Bint-CN have zero phonon lines at similar to 2.0 eV and similar to 2.6 eV, respectively. Defects involving Bint are likely to be the source of blue emitters recently observed in regions several microns away from ion-irradiated parts of hBN. Our work sheds light on these recent experiments and introduces a fresh perspective to the field of quantum emitters in hBN-we show that defects related to Bint are potential single-photon emitters that can be intentionally created in hBN.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor that is promising as a host material for solid-state quantum technologies through defect engineering. It has been shown that boron atoms can be removed from the lattice upon irradiation by electrons or light ions, creating boron vacancies and boron interstitials. While the optical properties of boron-vacancy-derived defects have been studied extensively, little is known about the optical properties of boron-interstitial-derived defects. In this work, we use state-of-the-art first-principles calculations to predict the electronic and optical properties of boron interstitials (Bint) and defect complexes comprising Bint and substitutional carbon impurities at boron and nitrogen sites (CB and CN). These carbon impurities can be present in as-grown hBN and can also be introduced intentionally. We demonstrate that these complexes are expected to be stable at room temperature. Our GW-Bethe-Salpeter equation (BSE) calculations show that Bint-CB and Bint-CN have low-energy optical transitions that are isolated in energy, making them suitable as single-photon emitters. Together with constrained density functional theory calculations to capture the red shift due to emission, we predict that Bint-CB and Bint-CN have zero phonon lines at similar to 2.0 eV and similar to 2.6 eV, respectively. Defects involving Bint are likely to be the source of blue emitters recently observed in regions several microns away from ion-irradiated parts of hBN. Our work sheds light on these recent experiments and introduces a fresh perspective to the field of quantum emitters in hBN-we show that defects related to Bint are potential single-photon emitters that can be intentionally created in hBN. |
Liang, Haidong; Chen, Yuan; Loh, Leyi; Cheng, Nicholas Lin Quan; Litvinov, Dmitrii; Yang, Chengyuan; Chen, Yifeng; Zhang, Zhepeng; Watanabe, Kenji; Taniguchi, Takashi; Koperski, Maciej; Quek, Su Ying; Bosman, Michel; Eda, Goki; Bettiol, Andrew Anthony Site-Selective Creation of Blue Emitters in Hexagonal Boron Nitride Journal Article ACS NANO, 19 (15), pp. 15130-15138, 2025, ISSN: 1936-0851. @article{ISI:001465855100001, title = {Site-Selective Creation of Blue Emitters in Hexagonal Boron Nitride}, author = {Haidong Liang and Yuan Chen and Leyi Loh and Nicholas Lin Quan Cheng and Dmitrii Litvinov and Chengyuan Yang and Yifeng Chen and Zhepeng Zhang and Kenji Watanabe and Takashi Taniguchi and Maciej Koperski and Su Ying Quek and Michel Bosman and Goki Eda and Andrew Anthony Bettiol}, doi = {10.1021/acsnano.5c03423}, times_cited = {5}, issn = {1936-0851}, year = {2025}, date = {2025-04-12}, journal = {ACS NANO}, volume = {19}, number = {15}, pages = {15130-15138}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Hexagonal boron nitride (hBN) has been of great interest due to its ability to host several bright quantum emitters at room temperature. However, the identification of the observed emitters remains challenging due to spectral variability, as well as the lack of atomic defect structure information. In this work, we demonstrate the site-selective creation of blue emitters in exfoliated hBN flakes with high-energy ion irradiation. With the correlation analysis of cryogenic and temperature-dependent photoluminescence (PL) spectroscopy, we observe two zero phonon lines (ZPLs) at similar to 432.8 and 454.3 nm. Photoluminescence excitation (PLE) measurements further confirm the emission origins of the two prominent lines. Scanning transmission electron microscopy (STEM) reveals that the dominant defect structures present in ion-irradiated samples are vacancy-type (V x ) and adatom(intercalant)-type (A x ). Together with first-principles GW-BSE (Bethe-Salpeter equation) calculations, we deduce that the observed blue emissions are likely related to boron intercalants (Bint). Our results not only discover a group of blue emissions in hBN but also provide insights into the physical origin of the emissions with local atomic structures in hBN.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Hexagonal boron nitride (hBN) has been of great interest due to its ability to host several bright quantum emitters at room temperature. However, the identification of the observed emitters remains challenging due to spectral variability, as well as the lack of atomic defect structure information. In this work, we demonstrate the site-selective creation of blue emitters in exfoliated hBN flakes with high-energy ion irradiation. With the correlation analysis of cryogenic and temperature-dependent photoluminescence (PL) spectroscopy, we observe two zero phonon lines (ZPLs) at similar to 432.8 and 454.3 nm. Photoluminescence excitation (PLE) measurements further confirm the emission origins of the two prominent lines. Scanning transmission electron microscopy (STEM) reveals that the dominant defect structures present in ion-irradiated samples are vacancy-type (V x ) and adatom(intercalant)-type (A x ). Together with first-principles GW-BSE (Bethe-Salpeter equation) calculations, we deduce that the observed blue emissions are likely related to boron intercalants (Bint). Our results not only discover a group of blue emissions in hBN but also provide insights into the physical origin of the emissions with local atomic structures in hBN. |
2021 |
Cheng, Nicholas Lin Quan; Xuan, Fengyuan; Spataru, Catalin D; Quek, Su Ying Charge Transfer Screening and Energy Level Alignment at Complex Organic-Inorganic Interfaces: A Tractable textitAb Initio GW Approach Journal Article JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 12 (36), pp. 8841-8846, 2021, ISSN: 1948-7185. @article{ISI:000697334300019, title = {Charge Transfer Screening and Energy Level Alignment at Complex Organic-Inorganic Interfaces: A Tractable textitAb Initio GW Approach}, author = {Nicholas Lin Quan Cheng and Fengyuan Xuan and Catalin D Spataru and Su Ying Quek}, doi = {10.1021/acs.jpclett.1c02302}, times_cited = {8}, issn = {1948-7185}, year = {2021}, date = {2021-09-07}, journal = {JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, volume = {12}, number = {36}, pages = {8841-8846}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Complex organic-inorganic interfaces are important for device and sensing applications. Charge transfer doping is prevalent in such applications and can affect the interfacial energy level alignments (ELA), which are determined by many-body interactions. We develop an approximate ab initio many-body GW approach that can capture many-body interactions due to interfacial charge transfer. The approach uses significantly less resources than a regular GW calculation but gives excellent agreement with benchmark GW calculations on an F4TCNQ/graphene interface. We find that many-body interactions due to charge transfer screening result in gate-tunable F4TCNQ HOMO-LUMO gaps. We further predict the ELA of a large system of experimental interest-4,4'-bis(dimethylamino)-bipyridine (DMAP-OED) on monolayer MoS2, where charge transfer screening results in an similar to 1 eV reduction of the molecular HOMO-LUMO gap. Comparison with a two-dimensional electron gas model reveals the importance of explicitly considering the intraband transitions in determining the charge transfer screening in organic-inorganic interface systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Complex organic-inorganic interfaces are important for device and sensing applications. Charge transfer doping is prevalent in such applications and can affect the interfacial energy level alignments (ELA), which are determined by many-body interactions. We develop an approximate ab initio many-body GW approach that can capture many-body interactions due to interfacial charge transfer. The approach uses significantly less resources than a regular GW calculation but gives excellent agreement with benchmark GW calculations on an F4TCNQ/graphene interface. We find that many-body interactions due to charge transfer screening result in gate-tunable F4TCNQ HOMO-LUMO gaps. We further predict the ELA of a large system of experimental interest-4,4'-bis(dimethylamino)-bipyridine (DMAP-OED) on monolayer MoS2, where charge transfer screening results in an similar to 1 eV reduction of the molecular HOMO-LUMO gap. Comparison with a two-dimensional electron gas model reveals the importance of explicitly considering the intraband transitions in determining the charge transfer screening in organic-inorganic interface systems. |
2019 |
Noori, Keian; Cheng, Nicholas Lin Quan; Xuan, Fengyuan; Quek, Su Ying Dielectric screening by 2D substrates Journal Article 42 2D MATERIALS, 6 (3), 2019, ISSN: 2053-1583. @article{ISI:000470869000001, title = {Dielectric screening by 2D substrates}, author = {Keian Noori and Nicholas Lin Quan Cheng and Fengyuan Xuan and Su Ying Quek}, doi = {10.1088/2053-1583/ab1e06}, times_cited = {42}, issn = {2053-1583}, year = {2019}, date = {2019-07-01}, journal = {2D MATERIALS}, volume = {6}, number = {3}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {Two-dimensional (2D) materials are increasingly being used as active components in nanoscale devices. Many interesting properties of 2D materials stem from the reduced and highly non-local electronic screening in two dimensions. While electronic screening within 2D materials has been studied extensively, the question still remains of how 2D substrates screen charge perturbations or electronic excitations adjacent to them. Thickness-dependent dielectric screening properties have recently been studied using electrostatic force microscopy (EFM) experiments. However, it was suggested that some of the thickness-dependent trends were due to extrinsic effects. Similarly, Kelvin probe measurements (KPM) indicate that charge fluctuations are reduced when BN slabs are placed on SiO2, but it is unclear if this effect is due to intrinsic screening from BN. In this work, we use first principles calculations to study the fully non-local dielectric screening properties of 2D material substrates. Our simulations give results in good qualitative agreement with those from EFM experiments, for hexagonal boron nitride (BN), graphene and MoS2, indicating that the experimentally observed thickness-dependent screening effects are intrinsic to the 2D materials. We further investigate explicitly the role of BN in lowering charge potential fluctuations arising from charge impurities on an underlying SiO2 substrate, as observed in the KPM experiments. 2D material substrates can also dramatically change the HOMO-LUMO gaps of adsorbates, especially for small molecules, such as benzene. We propose a reliable and very quick method to predict the HOMOLUMO gaps of small physisorbed molecules on 2D and 3D substrates, using only the band gap of the substrate and the gas phase gap of the molecule.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) materials are increasingly being used as active components in nanoscale devices. Many interesting properties of 2D materials stem from the reduced and highly non-local electronic screening in two dimensions. While electronic screening within 2D materials has been studied extensively, the question still remains of how 2D substrates screen charge perturbations or electronic excitations adjacent to them. Thickness-dependent dielectric screening properties have recently been studied using electrostatic force microscopy (EFM) experiments. However, it was suggested that some of the thickness-dependent trends were due to extrinsic effects. Similarly, Kelvin probe measurements (KPM) indicate that charge fluctuations are reduced when BN slabs are placed on SiO2, but it is unclear if this effect is due to intrinsic screening from BN. In this work, we use first principles calculations to study the fully non-local dielectric screening properties of 2D material substrates. Our simulations give results in good qualitative agreement with those from EFM experiments, for hexagonal boron nitride (BN), graphene and MoS2, indicating that the experimentally observed thickness-dependent screening effects are intrinsic to the 2D materials. We further investigate explicitly the role of BN in lowering charge potential fluctuations arising from charge impurities on an underlying SiO2 substrate, as observed in the KPM experiments. 2D material substrates can also dramatically change the HOMO-LUMO gaps of adsorbates, especially for small molecules, such as benzene. We propose a reliable and very quick method to predict the HOMOLUMO gaps of small physisorbed molecules on 2D and 3D substrates, using only the band gap of the substrate and the gas phase gap of the molecule. |