Browsing by Author "Pong, W. F."

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Determination of the microstructure of Eu-treated ZnO nanowires by x-ray absorption
(2010-02-08)
Huang, W. L.
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Labis, J.
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Ray, S. C.
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Liang, Y. R.
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Pao, C. W.
X-ray absorption near-edge structure (XANES), extended x-ray absorption fine structures (EXAFS), and photoluminescence measurements were used to elucidate the microstructural and photoluminescence properties of ZnO nanowires (ZnO-NWs) that had been treated with Eu by thermal diffusion. The O K- and Eu L(3)-edge XANES and EXAFS spectra at the Zn K- and Eu L(3)-edge verified the formation of Eu(2)O(3)-like layer on the surface of ZnO-NWs. X-ray diffraction, XANES and EXAFS measurements consistently suggest the lack of substitutional doping of Eu ions at the Zn ion sites in the interior of ZnO-NWs. The clear sharp and intense emission bands in the range 610-630 nm of Eu-treated ZnO-NWs originated from the intra-4f transition of Eu ions in the Eu(2)O(3)-like surface layer.
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.
Effect of geometry on the magnetic properties of CoFe2O4-PbTiO3 multiferroic composites
(2013)
Wang, B. Y.
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Wang, H. T.
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Singh, Shashi B.
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Shao, Y. C.
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Wang, Y. F.
In this study, X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray magnetic circular dichroism (XMCD) and element-and site-specific magnetic hysteresis (ESMH) are used to elucidate the effect of geometry (0-3- and 2-2-type) on the magnetic properties of CoFe2O4-PbTiO3 (CFO-PTO) multiferroic composites by comparison with those of the reference CFO and PTO powders. Magnetic Co ions in CFO have been confirmed to be located at both the tetrahedral (A)- and octahedral (B)-sites. CFO retains its mixed-spinel structure as verified by the EXAFS, XMCD and ESMH measurements. ESMH measurements further demonstrate that the magnetic moments of Co2+ and Fe3+/Fe2+ cations at both the A-and B-sites in the composites are smaller than those of the CFO powder. The reduction of the magnetic moments in the 2-2-type composite was larger than that in the 0-3-type composite. The reduction of the magnetic moments in the composites was attributable to the formation of anti-phase boundaries owing to the compressive strain in CFO, which is the largest strain in the 2-2-type composite. Based on the Ti L-3,L-2-edge XMCD measurements of the CFO-PTO composites, no induced magnetic moment was observed at the Ti sites in the PTO matrix, excluding the possibility that the Ti ions in the PTO matrix affect the magnetic properties of these CFO-PTO composites.
Local atomic and electronic structures and ferroelectric properties of PbZr(0.52)Ti(0.48)O(3): An x-ray absorption study (vol 99, 042909, 2011)
(2011-11-28)
Ray, S. C.
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Hsueh, H. C.
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Wu, C. H.
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Pao, C. W.
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Asokan, K.
Local atomic and electronic structures and ferroelectric properties of PbZr0.52Ti0.48O3: An x-ray absorption study (vol 99, 042909, 2011)
(2011-11-28)
Ray, S. C.
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Hsueh, H. C.
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Wu, C. H.
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Pao, C. W.
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Asokan, K.
Loycal atomic and electronic structures and ferroelectric properties of PbZr(0.52)Ti(0.48)O(3): An x-ray absorption study
(2011-07-25)
Ray, S. C.
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Hsueh, H. C.
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Wu, C. H.
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Pao, C. W.
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Asokan, K.
This work investigates local atomic and electronic structures of PbZr(0.52)Ti(0.48)O(3) (PZT) thin films with < 001 >, < 101 >, and < 111 > orientations using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy with theta = 0 degrees and 70 degrees incident angles. The EXAFS result indicates that the < 001 >-oriented PZT film has a polarization dominantly along the c-axis, while both < 101 >- and < 111 >-oriented PZT films have a dominant in-ab-plane polarization. The hysteresis-loop measurements show that the < 001 >-oriented PZT film has a much larger coercive field than those of other two PZT films, which indicates that the double-well potential along the c-axis is much deeper than that in the ab-plane. (C) 2011 American Institute of Physics. [doi:10.1063/1.3607475]
Loycal atomic and electronic structures and ferroelectric properties of PbZr0.52Ti0.48O3: An x-ray absorption study
(2011-07-25)
Ray, S. C.
;
Hsueh, H. C.
;
Wu, C. H.
;
Pao, C. W.
;
Asokan, K.
This work investigates local atomic and electronic structures of PbZr0.52Ti0.48O3 (PZT) thin films with < 001 >, < 101 >, and < 111 > orientations using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy with theta = 0 degrees and 70 degrees incident angles. The EXAFS result indicates that the < 001 >-oriented PZT film has a polarization dominantly along the c-axis, while both < 101 >- and < 111 >-oriented PZT films have a dominant in-ab-plane polarization. The hysteresis-loop measurements show that the < 001 >-oriented PZT film has a much larger coercive field than those of other two PZT films, which indicates that the double-well potential along the c-axis is much deeper than that in the ab-plane. (C) 2011 American Institute of Physics. [doi:10.1063/1.3607475]
Size dependence of the electronic structures and electron-phonon coupling in ZnO quantum dots
(2007-12-24)
Ray, S. C.
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Low, Y.
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Tsai, H. M.
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Pao, C. W.
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Chiou, J. W.
The electronic structures and optical properties of various sizes of ZnO quantum dots (QDs) were studied using x-ray absorption, photoluminescence, and Raman spectroscopy. The increase in the intensity ratio of the second-order Raman spectra of longitudinal optical mode and its fundamental mode, which is related to the strength of the electron-phonon coupling (EPC), is found to increase with the size of QD. The trend of EPC also correlates with the increase of the intensity ratio of the O 2p(pi) (I(pi)) and 2p(sigma) (I(sigma)) orbital features in the O K-edge x-ray absorption near-edge structure (XANES) as the size of QD increases. The EPC and XANES results suggest that the crystal orientations of ZnO QDs are approximately aligned with the c axis parallel with the polarization of x-ray photons. (c) 2007 American Institute of Physics.