Browsing by Author "Lee, C. S."

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Electrical characterization and Raman spectroscopy of individual vanadium pentoxide nanowire
(2011-10-01)
Shen, W. -J.
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Sun, K. W.
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Lee, C. S.
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應用化學系
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Department of Applied Chemistry
We measured I-V characteristics, electrical resistance, and Raman spectra in the temperature range from room temperature to above 600 K to obtain nanodevices. Measurements were taken on a single V(2)O(5) nanowire deposited on a Si template, where two- and four-point metallic contacts were previously made using e-beam lithography. In both two- and four-point probe measurements, the I-V curves were clearly linear and symmetrical with respect to both axes. Drastic reduction in electrical resistance and deviation from single valued activation energy with increasing temperature indicated phase transitions taking place in the nanowire. From temperature-dependent HR-Micro Raman measurements, reductions from V(2)O(5) to VO(2)/V(2)O(3) phases took place at a temperature as low as 500 K, when electrons were injected to the nanowire through electrical contacts.
Growth and characterization of LuVO4 single crystals
(2017-09-01)
Dimitrov, D. Z.
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Rafailov, P. M.
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Chen, Y. F.
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Lee, C. S.
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Todorov, R.
Large LuVO4 single crystals have been successfully obtained by high-temperature solution method. The structure details of these crystals are determined by X-ray crystallographic analysis and Raman spectroscopy. It is observed that the crystal consists of LuVO4 phase with trace amount of imperfections possibly due to oxygen vacancies. The optical quality of the crystal is assessed by Spectroscopic Ellipsometry (SE). The crystal shows higher than +0.2 birefringence in a large interval of wavelengths. (C) 2017 Elsevier B.V. All rights reserved.
Mechanism of Ethanol Reforming: Theoretical Foundations
(2009-04-23)
Wang, Jeng-Han
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Lee, C. S.
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Lin, M. C.
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應用化學系
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應用化學系分子科學碩博班
The mechanism of ethanol reforming has been systematically studied by both energetic calculation to examine ethanol decomposition and electronic structure analysis to investigate the redox capability of the nine selected metals of Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au with the same crystal structure and surface orientation. The energetic calculation shows that most of the dissociation barriers are lower on Co(111), Ni(111), Rh(111), and Ir(111.) surfaces and higher on Cu(111), Ag(111), and Au(111) surfaces. The initial C-H bond dissociation, forming the doubly adsorbed *C(H(2))C(H(2))O(H)* and *C(H(2))C(H(2))O*, with a lower barrier than those in the initial C-C and C-O bond dissociations is considered as the most feasible decomposition route. In addition, the linear correlation between reaction barriers and d-band centers breaks down in the case of C-H bond dissociation due to the lower barriers on Rh(111) and Ir(111) surfaces. This result may be related to the suitable bond distances on Rh(111) and Ir(111) surfaces to form the more stable double adsorbates, *C(H(2))C(H(2))O(H):* and *C(H(2))C(H(2))O*. In the electronic structure analysis, Rh(111) and Ir(111) surfaces with higher density of state (DOS) distributions around the Fermi level can efficiently accept/donate electrons from/to the reacting ethanol and its fragments, showing better redox capability. Therefore, the excellent efficiency of Rh- and Ir-based catalysts, as observed from the reforming experiment, can be attributed to both the lower decomposition barrier and the higher DOS distribution around the Fermi level based on the first-principles calculation.
Self-protecting dual-ring-architecture in time-sharing passive optical network to prevent the occurrence of fiber failure
(2008-03-15)
Yeh, C. H.
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Lee, C. S.
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Chi, S.
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光電工程學系
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Department of Photonics
We propose and experimentally investigate a self-protecting dual-ring-architecture time-division-multiplexed passive optical network (TDM-PON) using bidirectional dual-fiber path against the fiber-fault. By the proposed access network, the ring-based TDM-PON system can be revived promptly under single fiber failure. This restorable time is achieved within a few ms in the proposed ring access network. Moreover, the performance of data traffic in the optical access network has also discussed. (C) 2007 Elsevier B.V. All rights reserved.
Structural and optical properties of LuVO4 single crystals
(2017-01-01)
Dimitrov, D.
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Rafailov, P.
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Marinova, V.
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Babeva, T.
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Goovaerts, E.
The synthesis of large single crystals with good optical quality which is a preliminary condition for the practical applications of these materials frequently is complicated. It is found that large LuVO4 single crystals with high optical quality are possible to be prepared using high temperature solution growth method. It is obtained by X-ray crystallographic analysis that the grown crystals possess centrosymmetric tetragonal structure with the point group symmetry D-4h and space group I41/amd (zircon-type structure). The unit cell parameters of a = 7.0236 angstrom, b = 7.0236 angstrom, c = 6.2293 angstrom, volume = 307.30(3) angstrom(3) are measured. The crystals composition as well as vanadium oxidation state were measured in order to confirm that the crystal phase is mainly LuVO4. Optical transmission and Raman Spectroscopy are further performed on LuVO4 single crystal to reveal the optical quality and structure details