| 1. |
- Yang, Zhilin, et al.
(author)
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Surface enhanced Raman scattering of pyridine adsorbed on Au@Pd core/shell nanoparticles
- 2009
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:23
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Journal article (peer-reviewed)abstract
- Surface enhanced Raman scattering (SERS) of pyridine adsorbed on Au@Pd core/shell nanoparticles has been investigated theoretically with quantum chemical method, generalized Mie theory and three-dimensional finite-difference time domain (3D-FDTD) method. We first studied the influence of the coated Pd on the electronic structure of Au nanoparticle, and compared the electronic structure of Au-20 cluster with that of Au10Pd10 (core/shell) cluster. Second, we studied SERS spectroscopy of pyridine on Au@Pd core/shell nanoparticles, which revealed the rate of static chemical enhancement and electromagnetic enhancement in the experimental reports. Third, the influence of the Pd shell thickness to the optical absorption of Au@Pd core/shell nanoparticles was investigated with generalized Mie theory. Fourth, we studied the influence of the shell thickness to the local electric field enhancement with 3D-FDTD method. The theoretical results reveal that the static chemical enhancement and electromagnetic enhancement are in the order of 10 and 10(3), respectively. These theoretical studies promote the deeper understanding of the electronic structure and optical absorption properties of Au@Pd, and the mechanisms for SERS of molecule adsorbed on Au@Pd.
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| 2. |
- Sun, Mengtao, et al.
(author)
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Direct visual evidence for chemical mechanisms of SERRS via charge transfer in Au-20-pyrazine-Au-20 junction
- 2009
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In: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 40:12, s. 1942-1948
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Journal article (peer-reviewed)abstract
- The essence of the chemical mechanism for surface-enhanced resonance Raman scattering (SERRS) is the charge transfer (CT) between the metal and the molecule at the resonant electronic transition, which results in the mode-selective enhancement in the SERRS spectrum. The site-orientated CT can directly interpret the mode-selective chemical enhancement in SERRS. However, it is a great challenge to intutively visualize the orientation and site of the CT. In this paper, for the pyrazine-Au-2 complex, a three-dimensional [3D) cubic representation is built to provide direct visual evidence for chemical mechanisms of SERRS via CT from the Au-2 cluster to pyrazine at the resonant electronic transition. The relationship between the mode-selective enhancements in SERRS and the site-orientated CT was clearly revealed. The intracluster excitation (analog of plasmon excitation in large naonoparticles) was also visualized by the 3D cubic presentation, which provided the direct evidence of local electromagnetic field enhancement of SERRS. To study the quantum size effect and the coupling effect of the nanoparticles, the photoexcitation mechanisms of the Au-20 - pyrazine complex and the Au-20 - pyrazine - Au-20 junction were also investigated. The tunneling charge transfer from one Au-20 cluster to another Au-20 cluster outside the pyrazine in Au-20 - pyrazine - Au-20 junction was also revealed visually. The calculated normalized extinction spectra of Au nanoparticles using the generalized Mie theory reveal that the resonance peak is red-shifted due to the coupling between particles. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 3. |
- Sun, Mengtao, et al.
(author)
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Direct visual evidence for the chemical mechanism of surface-enhanced resonance Raman scattering via charge transfer: (II) Binding-site and quantum-size effects
- 2009
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In: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 40:9, s. 1172-1177
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Journal article (peer-reviewed)abstract
- We describe quantum-size and binding-site effects on the chemical and local field enhancement mechanisms of surface-enhanced resonance Raman scattering (SERRS), in which the pyridine molecule is adsorbed on one of the vertices of the Ag-20 tetrahedron. We first investigated the influence of the binding site on normal Raman scattering (NRS) and excited state properties of optical absorption spectroscopy. Second, we investigated the quantum-size effect on the electromagnetic (EM) and chemical mechanism from 300 to 1000 nm with charge difference density. It is found that the strong absorption at around 350 nm is mainly the charge transfer (CT) excitation (CT between the molecule and the silver cluster) for large clusters, which is the direct evidence for the chemical enhancement mechanism for SERRS; for a small cluster the strong absorption around 350 nm is mainly intracluster excitation, which is the direct evidence for the EM enhancement mechanism. This conclusion is further confirmed with the general Mie theory. The plasmon peak in EM enhancement will be red-shifted with the increase of cluster size. The influence of the binding site and quantum-size effects on NRS, as well as chemical and EM enhancement mechanisms on SERRS, is significant. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 4. |
- Sun, Mengtao, et al.
(author)
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Intermolecular charge and energy transfer in neurosporene and chlorophyll a derivative complex
- 2005
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 412:4-6, s. 425-429
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Journal article (peer-reviewed)abstract
- Dye-sensitized solar cells using a chlorophyll a derivative (PPB a der.) as the sensitizer and carotenoids having different conjugation lengths as redox spacers was studied experimentally. In this Letter, the excited state properties of the neurosporene & PPB a der. complex are investigated theoretically with quantum chemistry method. The 2D real space analysis with the transition density matrix reveals that some excited states are locally excited states, and some is the intermolecular charge transfer (ICT) state. The 3D real space analysis reveals: (1) that the orientation and the strength of the dipole moment from transition density, and (2) the orientation and result of ICT in Neurosporene & PPB a der. complex from charge difference density. (c) 2005 Elsevier B.V. All rights reserved.
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