Browsing by Author "Liu, Y. W."

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Density-dependent energy relaxation of hot electrons in InN epilayers
(2009-01-01)
Yang, M. D.
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Liu, Y. W.
;
Shen, J. L.
;
Chen, C. W.
;
Chi, G. C.
This work investigates the dependence of the hot-electron energy relaxation in InN epilayers on electron density. From the high-energy tail of photoluminescence, the electron temperature of the hot electrons was determined. Acoustic phonons have an important role in the energy relaxation of the hot electrons. The density-dependent electron energy loss rate in InN can be explained by a combination of longitudinal optical and acoustic phonon emissions. A slowing of energy loss rate at high electron densities was observed and attributed to piezoelectric coupling to acoustic phonons. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3056383]
The structure and photocatalytic activity of TiO2 thin films deposited by dc magnetron sputtering
(2012-12-01)
Yang, W. J.
;
Hsu, C. Y.
;
Liu, Y. W.
;
Hsu, R. Q.
;
Lu, T. W.
This paper seeks to determine the optimal settings for the deposition parameters, for TiO2 thin film, prepared on non-alkali glass substrates, by direct current (dc) sputtering, using a ceramic TiO2 target in an argon gas environment. An orthogonal array, the signal-to-noise ratio and analysis of variance are used to analyze the effect of the deposition parameters. Using the Taguchi method for design of a robust experiment, the interactions between factors are also investigated. The main deposition parameters, such as dc power (W), sputtering pressure (Pa), substrate temperature (degrees C) and deposition time (min), were optimized, with reference to the structure and photocatalytic characteristics of TiO2. The results of this study show that substrate temperature and deposition time have the most significant effect on photocatalytic performance. For the optimal combination of deposition parameters, the (110) and (200) peaks of the rutile structure and the (200) peak of the anatase structure were observed, at 2 theta similar to 27.4 degrees, 39.2 degrees and 48 degrees, respectively. The experimental results illustrate that the Taguchi method allowed a suitable solution to the problem, with the minimum number of trials, compared to a full factorial design. The adhesion of the coatings was also measured and evaluated, via a scratch test. Superior wear behavior was observed, for the TiO2 film, because of the increased strength of the interface of micro-blasted tools. (C) 2012 Elsevier Ltd. All rights reserved.