Browsing by Author "Wu, Chih-Wei"

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Blue/near UV light emission from hybrid InN/TiO(2) nanoparticle films
(2011-01-01)
Wu, Chih-Wei
;
Lu, Chih-Wei
;
Lee, Yuan-Pern
;
Wu, Yu-Jong
;
Cheng, Bing-Ming
We report on the enhancement of photoluminescence (PL) from anatase TiO(2) thin films covered by InN nanoparticles prepared using plasma enhanced chemical vapor deposition (PECVD). The SEM images and X-ray diffraction spectra illustrate the strong interaction between the InN particles and the TiO(2) films. UV-Vis absorption spectra indicate that the InN particles have an increased absorption in the visible light region and may sensitize the TiO(2) films. The strong PL band observed in the anatase TiO(2) thin films with the addition of InN may have been due to an increased localization of impurities and/or defect-trapped excitons.
Blue/near UV light emission from hybrid InN/TiO2 nanoparticle films
(2011-01-01)
Wu, Chih-Wei
;
Lu, Chih-Wei
;
Lee, Yuan-Pern
;
Wu, Yu-Jong
;
Cheng, Bing-Ming
We report on the enhancement of photoluminescence (PL) from anatase TiO2 thin films covered by InN nanoparticles prepared using plasma enhanced chemical vapor deposition (PECVD). The SEM images and X-ray diffraction spectra illustrate the strong interaction between the InN particles and the TiO2 films. UV-Vis absorption spectra indicate that the InN particles have an increased absorption in the visible light region and may sensitize the TiO2 films. The strong PL band observed in the anatase TiO2 thin films with the addition of InN may have been due to an increased localization of impurities and/or defect-trapped excitons.
CARBON-DOPED TiO2 NANOTUBES: EXPERIMENTAL AND COMPUTATIONAL STUDIES
(2013-05-01)
Huang, Wen-Fei
;
Wu, Pin-Jiun
;
Hsu, Wei-Chih
;
Wu, Chih-Wei
;
Liang, K. S.
C-doped TiO2 nanotubes (NTs) with anatase structure, prepared by anodizing the polished Ti foils, were characterized using X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and synchrotron-based X-ray photoemission spectroscopy (XPS). XPS results show electron losses in C atoms, no electron change in Ti atoms, and two doping energy levels appeared in band gaps. Structural geometries, DOSs, PDOSs, and Bader charge analyses of C-doped TiO2 anatase are predicted by periodic DFT calculations. Eight doping positions were taken into consideration: two substitutional cases (in oxygen and titanium sites) and six interstitial cases. We found that the interstitial carbon doping type is the most stable one, whereas the substitutional cases are rather unstable. Band-gap modifications can also be found in oxygen substitution, but not in titanium substitution. Both band-gap modification and non-band-gap modification are found in the interstitial carbon doping. In these eight C-doping systems, only the C atom in the oxygen substitution case gains electrons, 1.14 e, and others present electron losses within 0.5-4.00 e. The results of XPS measurements, DOSs calculations, and Bader charge analyses show that carbon interstitial is the most likely doping type for the C-doped TiO2 NTs.
Experimental and theoretical studies of rate coefficients for the reaction O(P-3) plus C2H5OH at high temperatures
(2007-07-26)
Wu, Chih-Wei
;
Lee, Yuan-Pern
;
Xu, Shucheng
;
Lin, M. C.
;
應用化學系
Rate coefficients of the reaction O(P-3) + C2H5OH in the temperature range 782-1410 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO2 at 193 nm with an ArF excimer laser; their concentrations were monitored via atomic resonance absorption. Our data in the range 886-1410 K are new. Combined with previous measurements at low temperature, rate coefficients determined for the temperature range 297-1410 K are represented by the following equation: k(T) = (2.89 +/- 0.09) x 10(-16)T(1.62) exp[-(1210 +/- 90)/T] cm(3) molecule(-1) s(-1); listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311+G(3df, 2p)//B3LYP/6-311+G(3df) level predict potential energies of various reaction paths. Rate coefficients are predicted with the canonical variational transition state (CVT) theory with the small curvature tunneling correction (SCT) method. Reaction paths associated with trans and gauche conformations are both identified. Predicted total rate coefficients, 1.60 x 10(-22)T(3.50) exp(16/T) cm(3) molecule(-1) s(-1) for the range 300-3000 K, agree satisfactorily with experimental observations. The branching ratios of three accessible reaction channels forming CH3CHOH + OH (1a), CH2CH2OH + OH (1b), and CH3CH2O + OH (1c) are predicted to vary distinctively with temperature. Below 500 K, reaction 1a is the predominant path; the branching ratios of reactions 1b,c become similar to 40% and similar to 11%, respectively, at 2000 K.
Shock Tube Study on the Thermal Decomposition of Ethanol
(2011-07-21)
Wu, Chih-Wei
;
Matsui, Hiroyuki
;
Wang, Niann-Shiah
;
Lin, M. C.
;
應用化學系
The thermal decomposition of C(2)H(5)OH highly diluted in Ar (1 and 3 ppm) has been studied by monitoring H atoms using the atomic resonance absorption spectrometry (ARAS) technique behind reflected shock waves over the temperature range 1450-1760 K at fixed pressure: 1, 1.45, and 2 atm. The rate constant and the product branching fractions have been determined by analyzing temporal profiles of H atoms; the effect of the secondary reactions on the results has been examined by using a detailed reaction mechanism composed of 103 elementary reactions. The apparent rate constant of ethanol decomposition can be expressed as k(1)/s(-1) = (5.28 +/- 0.14) x 10(10) exp[-(23 530 +/- 980)/T] (T = 1450-1670 K, P = 1-2 atm) without a detectable pressure dependence within the tested pressure range of this study. Branching fractions for producing CH(3) + CH(2)OH (1a) and H(2)O + C(2)H(4) (1b) have been examined by a quantitative measurement of H atoms produced in the successive decompositions of the products CH(2)OH (1a): the pressure dependence of the branching fraction for channel 1a is obtained by a linear least-squares analysis of the experimental data and can be expressed as phi(1a) = (0.71 +/- 0.07) - (826 +/- 116)/T, (0.92 +/- 0.04) (1108 +/- 70)/T, and (1.02 +/- 0.10) (1229 +/- 168)/T for T = 1450-1760 K, at P = 0.99, 1.45, and 2.0 atm, respectively. The rate constant obtained in this study is found to be consistent with previous theoretical and experimental results; however, the pressure dependence of the branching fraction obtained in this study is smaller than those of previous theoretical works. Modification of the parameters for the decomposition rate in the falloff region is suggested to be important to improve the practical modeling of the pyrolysis and combustion of ethanol