Browsing by Author "Chang, H. W."

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Effect of Fe2O3 coating on ZnO nanowires in photoelectrochemical water splitting: A synchrotron x-ray spectroscopic and spectromicroscopic investigation
(2020-06-01)
Lu, Y. R.
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Wang, Y. F.
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Chang, H. W.
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Huang, Y. C.
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Chen, J. L.
An array of ZnO/Fe2O3 core-shell nanowires (NW) for the highly efficient absorption of light and carrier collection is developed for use in photoelectrochemical (PEC) water-splitting. The oriented NW architecture favors physical matching, providing a direct electron conduction pathway and reducing the diffusion length of photogenerated holes. This work involves a combination of spectral imaging, spectromicroscopy and in situ x-ray absorption spectroscopy; spectra are obtained under operando conditions. Direct investigation of oriented nanowires using polarization-dependent x-ray spectromicroscopy enables the determination of the relationship between anisotropic electronic orbitals and charge carrier water-splitting efficiency. The results of O K-edge STXM demonstrated that the ZnO/Fe2O3 core-shell NW exhibits strong anisotropy and thus provides higher electron-hole transport efficiency than bare ZnO. In situ XAS revealed that interfacial charge transfer between Fe 3d and Zn 4p states enhances the photoelectrochemical reaction in the ZnO/Fe2O3 core-shell NW. The photogenerated electrons of Fe2O3 are transferred from Fe 3d states to the Zn 4p state under photoelectrochemical conditions.
Electrical and Optical Properties of a Single Sb(2)Se(3) Nanorod
(2009-06-01)
Ko, T. Y.
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Yang, C. H.
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Sun, K. W.
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Chang, H. W.
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Sarkar, B.
In this paper we present the methods to chemically synthesize the Sb(2)Se(3) nanorods and study the electrical and optical properties of a single Sb(2)Se(3) nanorod with an average size of 70 nm in diameter and a length of about 1 mu m to 2 mu m. The techniques we devised can immobilize and allocate a single nano-object on an electron beam (E-beam) patterned smart substrate. It can also overcome the limitation of the spatial resolution of conventional optical techniques (similar to 1 mu m) to obtain optical spectroscopy in an individual nano-object less than 100 nm in size. We also demonstrate the techniques in using E-beam defined metallic coordination markers as electrodes to measure the conductance of a single Sb(2)Se(3) nanorod.
Electrical and Optical Properties of a Single Sb2Se3 Nanorod
(2009-06-01)
Ko, T. Y.
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Yang, C. H.
;
Sun, K. W.
;
Chang, H. W.
;
Sarkar, B.
In this paper we present the methods to chemically synthesize the Sb2Se3 nanorods and study the electrical and optical properties of a single Sb2Se3 nanorod with an average size of 70 nm in diameter and a length of about 1 mu m to 2 mu m. The techniques we devised can immobilize and allocate a single nano-object on an electron beam (E-beam) patterned smart substrate. It can also overcome the limitation of the spatial resolution of conventional optical techniques (similar to 1 mu m) to obtain optical spectroscopy in an individual nano-object less than 100 nm in size. We also demonstrate the techniques in using E-beam defined metallic coordination markers as electrodes to measure the conductance of a single Sb2Se3 nanorod.
Magnetocaloric Properties of Melt-Spun Fe-Ni-Mn-Ga Ribbons
(2014-01-01)
Shih, C. W.
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Zhao, X. G.
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Chang, H. W.
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Tseng, Y. C.
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Chang, W. C.
The effects of Ni substitution for Fe on phase constitutions, Curie temperature T-C, and magnetocaloric properties of melt-spun Fe50-xNixMn25Ga25 (x =0, 1, 3, 5 and 7) ribbons have been investigated. X-ray diffraction results show that the main phase in the Fe50-xNixMn25Ga25 (x = 0-7) alloy changed with the increase of Ni content from FCC structure for x = 0 into B2 structure for x = 1-7. Besides, the magnetic phase exhibits phase transition of ferromagnetic into paramagnetic state with increasing temperature for the samples with B2-type structure. The Curie temperature T-C of these ribbons varies in the temperature range of 232-257 K. The peak values of the maximal magnetic entropy change, -Delta S-M(max), are about 1.4-1.6 Jkg/K for Ni-substituted ribbons at a maximum applied field of 30 kOe. On the other hand, the relatively broader temperature range at the half maximum of Delta S-M peak (similar to 90 K), low-cost and nontoxic elements make Fe-Ni-Mn-Ga-based ribbons the promising candidates for magnetic refrigeration applications close to room temperature.
Production of neutral fragments of gaseous SiCl4 following Si 2p core-level excitation studied by dispersed fluorescence spectroscopy
(2006-11-01)
Lu, K. T.
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Chen, J. M.
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Lee, J. M.
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Ho, S. C.
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Chang, H. W.
State-specific dissociation dynamics for ionic fragments and excited fragments of gaseous SiCl4 following Si 2p core-level excitation have been characterized by the dispersed UV/optical fluorescence spectroscopy and photionization mass spectroscopy. The Si 2p core-to-Rydberg excitation leads to a noteworthy production of excited atomic fragments, neutral and ionic (Si-*, Si+*). In particular, the excited neutral atomic fragments Si* are significantly reinforced. The Si 2p core-to-valence excitation generates an enhancement of excited molecular-ion SiCl4+. The experimental results provide deeper insight into the dissociation dynamics for excited neutral fragments of molecules via core-level excitation. (c) 2006 Elsevier Ltd. All rights reserved.