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268 results on '"Yam, ChiYung"'

51. Theoretical Insight into Optoelectronic Properties of All-Inorganic Copper-Based Perovskite Derivatives Cs2CuXCl6 (X = As, Sb, and Bi).

Author

Zuo, Tao, Qi, Fangfang, Yam, ChiYung, Jiang, Shanshan, Yang, Mingxue, Zhong, Ming-Long, and Meng, Lingyi

Abstract

All-inorganic lead-free perovskites are emerging to replace the hybrid halide perovskite materials for light converting technology because of their expected superior thermal stability. Herein, we theoretically investigate the thermal stability, electronic and optical properties of double perovskites based on arsenic, antimony and bismuth, by using the density functional theory (DFT). We optimize the geometrical structures and predict the stable chemical potential regions for Cs2CuXCl6 (X = As, Sb, and Bi), to analyze the chemical conditions for obtaining single-phase structures. Furthermore, we calculate the bandgap energies, effective masses and light absorption coefficients, and elucidate that the photoelectric properties of these Cu-based double perovskites are suitable for photovoltaic applications. Our investigations provide a new routine for the design of lead-free halide perovskite solar absorbers. [ABSTRACT FROM AUTHOR]

Published
2022
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67. Electron–Phonon Coupling in Current-Driven Single-Molecule Junctions

Author

Bi, Hai, primary, Palma, Carlos-Andres, additional, Gong, Yuxiang, additional, Stallhofer, Klara, additional, Nuber, Matthias, additional, Jing, Chao, additional, Meggendorfer, Felix, additional, Wen, Shizheng, additional, Yam, ChiYung, additional, Kienberger, Reinhard, additional, Elbing, Mark, additional, Mayor, Marcel, additional, Iglev, Hristo, additional, Barth, Johannes V., additional, and Reichert, Joachim, additional

Published
2020
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70. Generation and Detection of Strain-Localized Excitons in WS2Monolayer by Plasmonic Metal Nanocrystals

Author

Li, Shasha, Chui, Ka Kit, Shen, Fuhuan, Huang, He, Wen, Shizheng, Yam, ChiYung, Shao, Lei, Xu, Jianbin, and Wang, Jianfang

Abstract

Excitons in a transition-metal dichalcogenide (TMDC) monolayer can be modulated through strain with spatial and spectral control, which offers opportunities for constructing quantum emitters for applications in on-chip quantum communication and information processing. Strain-localized excitons in TMDC monolayers have so far mainly been observed under cryogenic conditions because of their subwavelength emission area, low quantum yield, and thermal-fluctuation-induced delocalization. Herein, we demonstrate both generation and detection of strain-localized excitons in WS2monolayer through a simple plasmonic structure design, where WS2monolayer covers individual Au nanodisks or nanorods. Enhanced emission from the strain-localized excitons of the deformed WS2monolayer near the plasmonic hotspots is observed at room temperature with a photoluminescence energy redshift up to 200 meV. The emission intensity and peak energy of the strain-localized excitons can be adjusted by the nanodisk size. Furthermore, the excitation and emission polarization of the strain-localized excitons are modulated by anisotropic Au nanorods. Our results provide a promising strategy for constructing nonclassical integrated light sources, high-sensitivity strain sensors, or tunable nanolasers for future dense nanophotonic integrated circuits.

Published
2022
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75. The spin–orbit interaction controls photoinduced interfacial electron transfer in fullerene–perovskite heterojunctions: C60versus C70.

Author

Yang, Jia-Jia, Liu, Xiang-Yang, Li, Zi-Wen, Frauenheim, Thomas, Yam, ChiYung, Fang, Wei-Hai, and Cui, Ganglong

Abstract

Here, we used collinear and noncollinear density functional theory (DFT) methods to explore the interfacial properties of two heterojunctions between a fullerene (C60 and C70) and the MAPbI3(110) surface. Methodologically, consideration of the spin–orbit interaction has been proven to be required to obtain accurate energy-level alignment and interfacial carrier dynamics between fullerenes and perovskites in hybrid perovskite solar cells including heavy atoms (such as Pb atoms). Both heterojunctions are predicted to be the same type-II heterojunction, but the interfacial electron transfer process from MAPbI3 to C60 is completely distinct from that to C70. In the former, the interfacial electron transfer is slow because of the associated large energy gap, and the excited electrons are thus trapped in MAPbI3 for a while. In contrast, in the latter, the smaller energy gap induces ultrafast electron transfer from MAPbI3 to C70. These points are further supported by DFT-based nonadiabatic dynamics simulations including the spin–orbit coupling (SOC) effects. These gained insights could help rationally design superior fullerene–perovskite interfaces to achieve high power conversion efficiencies of fullerene–perovskite solar cells. [ABSTRACT FROM AUTHOR]

Published
2021
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76. Frequency-domain multiscale quantum mechanics/electromagnetics simulation method.

Author

Meng, Lingyi, Yin, Zhenyu, Yam, ChiYung, Koo, SiuKong, Chen, Quan, Wong, Ngai, and Chen, GuanHua

Subjects
FREQUENCY-domain analysis, QUANTUM mechanics, ELECTROMAGNETISM, SIMULATION methods & models, BOUNDARY value problems, INFORMATION sharing, CARBON nanotubes, CURRENT density (Electromagnetism)
Abstract

A frequency-domain quantum mechanics and electromagnetics (QM/EM) method is developed. Compared with the time-domain QM/EM method [Meng et al., J. Chem. Theory Comput. 8, 1190-1199 (2012)], the newly developed frequency-domain QM/EM method could effectively capture the dynamic properties of electronic devices over a broader range of operating frequencies. The system is divided into QM and EM regions and solved in a self-consistent manner via updating the boundary conditions at the QM and EM interface. The calculated potential distributions and current densities at the interface are taken as the boundary conditions for the QM and EM calculations, respectively, which facilitate the information exchange between the QM and EM calculations and ensure that the potential, charge, and current distributions are continuous across the QM/EM interface. Via Fourier transformation, the dynamic admittance calculated from the time-domain and frequency-domain QM/EM methods is compared for a carbon nanotube based molecular device. [ABSTRACT FROM AUTHOR]

Published
2013
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77. Enhanced photocurrent in heterostructures formed between CH3NH3PbI3 perovskite films and graphdiyne.

Author

Bi, Fuzhen, Yam, ChiYung, Zhao, Chengjie, Liu, Le, Zhao, Min, Zheng, Xiao, and Jiu, Tonggang

Abstract

Extending photoabsorption to the near-infrared region (NIR) of the spectrum remains a major challenge for the enhancement of the photoelectric performance of perovskites. In this work, we propose a model of van der Waals heterostructures formed by CH3NH3PbI3 perovskite films and graphdiyne (GDY) to improve the photocurrent in the NIR. To obtain better insights into the properties of GDY/perovskite heterostructures, we first determine its electronic properties using the first principles calculations. The charge transfer between GDY and perovskites leads to a built-in electrical field that facilitates the separation and the transport of the photogenerated carriers. Then, the non-equilibrium Green's function (NEGF) is used to calculate the photocurrents of perovskite slabs with and without GDY. The photocurrents of GDY/perovskite heterostructures are nearly an order of magnitude larger than that of pristine perovskites in NIR due to the synergistic effect between GDY and perovskites. Furthermore, a polarization-sensitive photocurrent is obtained for a GDY/PbI2 heterostructure. [ABSTRACT FROM AUTHOR]

Published
2020
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85. Time-Dependent Current Distributions of a Two-Terminal Carbon Nanotube-Based Electronic Device

Author

Wen, Shizheng, Koo, SiuKong, Yam, ChiYung, Zheng, Xiao, Yan, YiJing, Su, Zhongmin, Fan, Kangnian, Cao, Li, Wang, Wenping, and Chen, GuanHua

Abstract

We have performed time-dependent density-functional theory calculations to simulate the transient electrical response of a carbon nanotube-based electronic device. Time-dependent current density and electrostatic potential distribution are calculated and analyzed. Strong local vortices are observed for the current. In addition, the calculated dynamic admittance confirms that the dynamic response of the two-terminal device can be mapped onto the equivalent electric circuit reported in our previous work [Yam et al.Nanotechnology 2008, 19, 495203].

Published
2024
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97. Time-Dependent Current Distributions of a Two-Terminal Carbon Nanotube-Based Electronic Device

Author

Wen, Shizheng, Koo, SiuKong, Yam, ChiYung, Zheng, Xiao, Yan, YiJing, Su, Zhongmin, Fan, Kangnian, Cao, Li, Wang, Wenping, Chen, GuanHua, Wen, Shizheng, Koo, SiuKong, Yam, ChiYung, Zheng, Xiao, Yan, YiJing, Su, Zhongmin, Fan, Kangnian, Cao, Li, Wang, Wenping, and Chen, GuanHua

Abstract

We have performed time-dependent density-functional theory calculations to simulate the transient electrical response of a carbon nanotube-based electronic device. Time-dependent current density and electrostatic potential distribution are calculated and analyzed. Strong local vortices are observed for the current. In addition, the calculated dynamic admittance confirms that the dynamic response of the two-terminal device can be mapped onto the equivalent electric circuit reported in our previous work [Yam et al. Nanotechnology 2008, 19, 495203].

Published
2011

98. Dynamic Admittance of Carbon Nanotube-Based Molecular Electronic Devices and their Equivalent Electric Circuit

Author

Yam, ChiYung, Mo, Yan, Wang, Fan, Li, Xiaobo, Chen, GuanHua, Zheng, Xiao, Matsuda, Yuki, Tahir-Kheli, Jamil, Goddard, III, William A., Yam, ChiYung, Mo, Yan, Wang, Fan, Li, Xiaobo, Chen, GuanHua, Zheng, Xiao, Matsuda, Yuki, Tahir-Kheli, Jamil, and Goddard, III, William A.

Abstract

We use first-principles quantum mechanics to simulate the transient electrical response through carbon nanotube-based conductors under time-dependent bias voltages. The dynamic admittance and time-dependent charge distribution are reported and analyzed. We find that the electrical response of these two-terminal molecular devices can be mapped onto an equivalent classical electric circuit and that the switching time of these end-on carbon nanotube devices is only a few femtoseconds. This result is confirmed by studying the electric response of a simple two-site model device and is thus generalized to other two-terminal molecular electronic devices.

Published
2008

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