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Salmanov VM, Guseinov AG, Mamedov RM, Salmanova AA, Gasanova LG, Magomedov AZ, Akhmedova FS. Effect of Laser Radiation on InSe and GaSe Thin Films Grown via Laser Sublimation and Chemical Deposition. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2018. [DOI: 10.1134/s0036024418090236] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Zhou N, Chen L, Huang Z, Sun K, Tanimura Y, Zhao Y. Fast, Accurate Simulation of Polaron Dynamics and Multidimensional Spectroscopy by Multiple Davydov Trial States. J Phys Chem A 2016; 120:1562-76. [PMID: 26871592 DOI: 10.1021/acs.jpca.5b12483] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
By employing the Dirac-Frenkel time-dependent variational principle, we study the dynamical properties of the Holstein molecular crystal model with diagonal and off-diagonal exciton-phonon coupling. A linear combination of the Davydov D1 (D2) ansatz, referred to as the "multi-D1 ansatz" ("multi-D2 ansatz"), is used as the trial state with enhanced accuracy but without sacrificing efficiency. The time evolution of the exciton probability is found to be in perfect agreement with that of the hierarchy equations of motion, demonstrating the promise the multiple Davydov trial states hold as an efficient, robust description of dynamics of complex quantum systems. In addition to the linear absorption spectra computed for both diagonal and off-diagonal cases, for the first time, 2D spectra have been calculated for systems with off-diagonal exciton-phonon coupling by employing the multiple D2 ansatz to compute the nonlinear response function, testifying to the great potential of the multiple D2 ansatz for fast, accurate implementation of multidimensional spectroscopy. It is found that the signal exhibits a single peak for weak off-diagonal coupling, while a vibronic multipeak structure appears for strong off-diagonal coupling.
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Affiliation(s)
- Nengji Zhou
- Department of Physics, Hangzhou Normal University , Hangzhou 310046, China.,Division of Materials Science, Nanyang Technological University , Singapore 639798, Singapore
| | - Lipeng Chen
- Division of Materials Science, Nanyang Technological University , Singapore 639798, Singapore
| | - Zhongkai Huang
- Division of Materials Science, Nanyang Technological University , Singapore 639798, Singapore
| | - Kewei Sun
- School of Science, Hangzhou Dianzi University , Hangzhou 310046, China
| | - Yoshitaka Tanimura
- Department of Chemistry, Graduate School of Science, Kyoto University , Kyoto 606-8502, Japan
| | - Yang Zhao
- Division of Materials Science, Nanyang Technological University , Singapore 639798, Singapore
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Lu R, Liu J, Luo H, Chikan V, Wu JZ. Graphene/GaSe-Nanosheet Hybrid: Towards High Gain and Fast Photoresponse. Sci Rep 2016; 6:19161. [PMID: 26776942 PMCID: PMC4726015 DOI: 10.1038/srep19161] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 12/02/2015] [Indexed: 11/09/2022] Open
Abstract
While high photoconductive gain has been recently achieved in graphene-based hybrid phototransistors using semiconductor two-dimensional transition/post-transition metal dichalcogenides or quantum dots sensitizers, obtaining fast photoresponse simutaneously remains a challenge that must be addressed for practical applications. In this paper we report a graphene/GaSe nanosheets hybrid photodetector, in which GaSe nanosheets provide a favorable geometric link to graphene conductive layer through van Der Waals force. After a vacuum annealing process, a high gain in exceeding 10(7) has been obtained simitaneously with a dynamic response time of around 10 ms for both light on and off. We attribute the high performance to the elimination of possible deep charge traps, most probably at the graphene/GaSe nanosheets interface. This result demonstrates high photoconductive gain and fast photoresponse can be achieved simultaneously and a clean interface is the key to the high performance of these hybrid devices.
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Affiliation(s)
- Rongtao Lu
- Department of Physics &Astronofmy, University of Kansas, Lawrence, KS 66045, USA
| | - Jianwei Liu
- Department of Physics &Astronofmy, University of Kansas, Lawrence, KS 66045, USA
| | - Hongfu Luo
- Department of Chemistry, Kansas State University, Manhattan, KS 66506
| | - Viktor Chikan
- Department of Chemistry, Kansas State University, Manhattan, KS 66506
| | - Judy Z Wu
- Department of Physics &Astronofmy, University of Kansas, Lawrence, KS 66045, USA
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Zhou N, Huang Z, Zhu J, Chernyak V, Zhao Y. Polaron dynamics with a multitude of Davydov D2 trial states. J Chem Phys 2015; 143:014113. [PMID: 26156471 DOI: 10.1063/1.4923009] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We propose an extension to the Davydov D2 Ansatz in the dynamics study of the Holstein molecular crystal model with diagonal and off-diagonal exciton-phonon coupling using the Dirac-Frenkel time-dependent variational principle. The new trial state by the name of the "multi-D2 Ansatz" is a linear combination of Davydov D2 trial states, and its validity is carefully examined by quantifying how faithfully it follows the Schrödinger equation. Considerable improvements in accuracy have been demonstrated in comparison with the usual Davydov trial states, i.e., the single D1 and D2 Ansätze. With an increase in the number of the Davydov D2 trial states in the multi-D2 Ansatz, deviation from the exact Schrödinger dynamics is gradually diminished, leading to a numerically exact solution to the Schrödinger equation.
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Affiliation(s)
- Nengji Zhou
- Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore
| | - Zhongkai Huang
- Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore
| | - Jiangfeng Zhu
- Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore
| | - Vladimir Chernyak
- Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore
| | - Yang Zhao
- Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore
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Abstract
The photophysics of mixed aggregates of GaSe/InSe nanoparticles have been studied using static and time-resolved absorption and emission spectroscopies. The results indicate that the GaSe/InSe interfaces form heterojunctions and exhibit photoinduced direct charge transfer from the GaSe valence band to the InSe conduction band. This results in the electrons and holes being localized separately in these two types of nanoparticles. The energy diagram of the nanoparticle heterojunction can be constructed from the static spectra, known bulk band offsets, and quantum confinement effects. These considerations accurately predict the energy of the observed charge-transfer band. Photoexcitation also produces excitons in the aggregates, away from the heterojunctions. These excitons can undergo diffusion and quench upon reaching a heterojunction. Time-resolved fluorescence kinetics can be modeled to extract an exciton diffusion coefficient. A value of 2.0 nm2/ns is obtained, which is in good agreement with values obtained from previous fluorescence anisotropy decay measurements.
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Affiliation(s)
- Xiang-Bai Chen
- Division of Natural Sciences, University of California at Merced, Merced, California 95344, USA
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Yang S, Kelley DF. Transient Absorption Spectra and Dynamics of InSe Nanoparticles. J Phys Chem B 2006; 110:13430-5. [PMID: 16821867 DOI: 10.1021/jp061870r] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Time-resolved fluorescence and transient absorption results have been obtained for small (approximately 3 nm) and large (approximately 5-8 nm) InSe nanoparticles in room-temperature solutions. The large particles are nonfluorescent, indicating that the conduction band is at M and the optical transition is forbidden. For some fraction of the small particles, the bottom of the conduction band is at Gamma and the optical transition is allowed. The small particle fluorescence measurements indicate that hole trapping occurs on the 200-300 ps time scale. The transient absorption spectra are featureless throughout the visible with a broad maximum at 600-650 nm. The transient absorption kinetics of both small and large particles show a 200-300 ps decay component that is assigned to hole trapping. These kinetics also show a 15 ps decay that has a larger amplitude in the case of the large particles and is assigned to an electron Gamma to M relaxation. The amplitude of this decay indicates that the initial electron and hole intraband transitions result in roughly comparable intensities of the initial transient absorption.
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Affiliation(s)
- Shuming Yang
- Division of Natural Sciences, University of California, Merced, Merced, California 95344, USA
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Tu H, Kelley DF. Photoinduced direct electron transfer from InSe to GaSe semiconductor nanoparticles. NANO LETTERS 2006; 6:116-22. [PMID: 16402798 DOI: 10.1021/nl051914s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Direct electron transfer from InSe nanoparticles to GaSe nanoparticles in mixed solution-phase aggregates has been found to occur upon photoexcitation. Mixed aggregates exhibit a strong charge-transfer absorption band at an energy slightly higher than the InSe band gap. Photoexcitation of this band results in a polarized transient absorption spectrum and transient absorption kinetics characteristic of InSe valence-band holes and GaSe conduction-band electrons. The kinetics indicate that charge separation persists for at least several hundred picoseconds.
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Affiliation(s)
- Haohua Tu
- University of California, Merced, 95344, USA
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Abstract
The synthesis of several different sizes of InSe nanoparticles from organometallic precursors is reported. These particles are characterized by transmission electron microscopy, electron diffraction, and optical spectroscopy. The electron diffraction results and optical properties indicate that these particles are two-dimensional disks, consisting of single Se-In-In-Se tetralayer sheets. The absorption spectra indicate strong quantum confinement along the z axis and, for the smaller particles, in the x,y plane. The z-axis quantum confinement may be quantitatively understood in terms of the band structure of bulk InSe. The results indicate that the z-axis quantum confinement reverses the order of the direct and indirect transitions in the case of the largest particles. The smaller particles exhibit strong, polarized fluorescence, and the fluorescence polarization may also be understood in terms of the band structure of bulk InSe.
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Affiliation(s)
- Shuming Yang
- Division of Natural Sciences, University of California, Merced, P.O. Box 2039, Merced, California 95344, USA
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Kloepfer JA, Bradforth SE, Nadeau JL. Photophysical Properties of Biologically Compatible CdSe Quantum Dot Structures. J Phys Chem B 2005; 109:9996-10003. [PMID: 16852208 DOI: 10.1021/jp044581g] [Citation(s) in RCA: 165] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photophysical properties of CdSe and ZnS(CdSe) semiconductor quantum dots in nonpolar and aqueous solutions were examined with steady-state (absorption and emission) and time-resolved (time-correlated single-photon-counting) spectroscopy. The CdSe structures were prepared from a single CdSe synthesis, a portion of which were ZnS-capped, thus any differences observed in the spectral behavior between the two preparations were due to changes in the molecular shell. Quantum dots in nonpolar solvents were surrounded with a trioctylphosphine oxide (TOPO) coating from the initial synthesis solution. ZnS-capped CdSe were initially brighter than bare uncapped CdSe and had overall faster emission decays. The dynamics did not vary when the solvent was changed from hexane to dichloromethane; however, replacement of the TOPO cap by pyridine affected CdSe but not ZnS(CdSe). CdSe was then solubilized in water with mercapto-acetic acid or dihydrolipoic acid, whereas ZnS(CdSe) could be solubilized only with dihydrolipoic acid. Both solubilization agents quenched the nanocrystal emission, though with CdSe the quenching was nearly complete. Additional quenching of the remaining emission was observed when the redox-active molecule adenine was conjugated to the water-soluble CdSe but was not seen with ZnS(CdSe). The emission of aqueous CdSe could be enhanced under prolonged exposure to room light and resulted in a substantial increase of the emission lifetimes; however, the enhancement occurred concurrently with precipitation of the nanocrystals, which was possibly caused by photocatalytic destruction of the mercaptoacetic acid coating. These results are the first presented on aqueous CdSe quantum dot structures and are presented in the context of designing better, more stable biological probes.
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Affiliation(s)
- Jeremiah A Kloepfer
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
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Tu H, Mogyorosi K, Kelley DF. Exciton dynamics of GaSe nanoparticle aggregates. J Chem Phys 2005; 122:44709. [PMID: 15740285 DOI: 10.1063/1.1835892] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Time-resolved and static spectroscopic results on GaSe nanoparticle aggregates are presented to elucidate the exciton relaxation and diffusion dynamics. These results are obtained in room-temperature TOP/TOPO solutions at various concentrations. The aggregate absorption spectra are interpreted in terms of electrostatic coupling and covalent interactions between particles. The spectra at various concentrations may then be interpreted in terms of aggregate distributions calculated from a simple equilibrium model. These distributions are used to interpret concentration-dependent emission anisotropy kinetics and time-dependent emission spectral shifts. The emission spectra are reconstructed from the static emission spectra and decay kinetics obtained at a range of wavelengths. The results indicate that the aggregate z axis persistence length is about 9 particles. The results also show that the one-dimensional exciton diffusion coefficient is excitation wavelength dependent and has a value of about 2 x 10(-5) cm(2)/s following 406 nm excitation. Although exciton diffusion results in very little energy relaxation, subsequent hopping of trapped electron/hole pairs occurs by a Forster mechanism and strongly red shifts the emission spectrum.
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Affiliation(s)
- H Tu
- University of California-Merced, Merced, CA 95344, USA
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Affiliation(s)
- H. Tu
- University of California, Merced, P. O. Box 2039, Merced, California 95344
| | - S. Yang
- University of California, Merced, P. O. Box 2039, Merced, California 95344
| | - V. Chikan
- University of California, Merced, P. O. Box 2039, Merced, California 95344
| | - D. F. Kelley
- University of California, Merced, P. O. Box 2039, Merced, California 95344
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Tu H, Chikan V, Kelley DF. Electron and Hole Intraband Spectroscopy of GaSe Nanoparticles. J Phys Chem B 2003. [DOI: 10.1021/jp034297+] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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