Browsing by Author "Wen, D. C."

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Evaluation of the characteristics of the microelectrical discharge machining process using response surface methodology based on the central composite design
(2012-10-01)
Lin, Y. C.
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Tsao, C. C.
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Hsu, C. Y.
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Hung, S. K.
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Wen, D. C.
Evaluation of the characteristics of a microelectrical discharge machining (Micro-EDM) process is challenging, because it involves complex, interrelated relationships so a proper modeling approach is necessary to clearly identify the crucial machining variables and their interrelationships in order to initiate more effective strategies to improve Micro-EDM qualities (electrode wear (EW), material removal rate (MRR) and overcut). This paper uses a response surface method (RSM) based on the central composite design (CCD) for Micro-EDM problems with four EDM variables (peak current, pulse on-time, pulse off-time and electrode rotation speed). Experimental results indicate that peak current is the EDM variable that most affects the Micro-EDM qualities for SK3 carbon tool steel while pulse off-time had a significant interaction with that. The results show that RSM based on the CCD could efficiently be applied for the modeling of Micro-EDM qualities (EW, MRR, and overcut), and it is an economical way to obtain the performance characteristics of Micro-EDM process parameters with the fewest experimental data.
Influence of TiO2 buffer layer and post-annealing on the quality of Ti-doped ZnO thin films
(2013-07-01)
Lin, Y. C.
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Hsu, C. Y.
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Hung, S. K.
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Wen, D. C.
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機械工程學系
Ti-doped ZnO (TZO) thin films were grown on soda lime glass (SLG) substrate without and with a TiO2 buffer layer by radio frequency magnetron sputtering and then annealed under vacuum at 450 and 500 degrees C for 20 min. The structural, electrical, and optical properties of TZO films were investigated. XRD analysis shows that all TZO films are highly textured along the c-axis and perpendicular to the substrate. The structural properties of TZO films are improved by controlling the annealing temperature and inserting a TiO2 buffer layer. When the films were annealed at 450 degrees C, the crystallinity increased, but it then decreased slightly with increase in annealing temperature from 450 to 500 degrees C. Due to superior crystallinity, TZO films annealed at 450 degrees C exhibited lower resistivity and higher average transmittances in the visible region. The improvements in crystallinity, resistivity and transmittance are more obvious when a TiO2 buffer layer was inserted. The decrease in resistivity is mainly attributed to an increase in Hall mobility rather than carrier concentration. When the TZO films deposited on bare SLG substrate, the energy band gaps was decreased after annealing at 450 and 500 degrees C due to the decrease in carrier concentration. However, the absorption edge of TZO films deposited on TiO2-buffered substrate was blue shifted, and the energy band gap was increased due to the increase of carrier concentration. In this study, the TZO film with optimal properties was grown on the TiO2-buffered substrate and post annealed at 450 degrees C, achieving a resistivity of 3.76 x 10(-3) Omega-cm and an average transmittance above 85%. Therefore, it can be concluded that inserting a buffer layer at an early stage of film deposition to improve crystallinity can help achieve low resistivity, high transmittance, and high energy band gap in transparent conducting TZO thin films. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
The structural and optoelectronic properties of Ti-doped ZnO thin films prepared by introducing a Cr buffer layer and post-annealing
(2012-10-01)
Lina, Y. C.
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Hsu, C. Y.
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Hung, S. K.
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Chang, C. H.
;
Wen, D. C.
This work investigates the effects of Cr buffer layers and post- annealing on the properties of titaniumdoped zinc oxide (TZO) thin films prepared by radio frequency magnetron sputter. All films had a (0 0 2) preferential orientation along the c-axis at 2 theta similar to 34 degrees. The crystallinity, grain size, Hall mobility and carrier concentration of TZO films were enhanced by introducing a Cr buffer layer and post-annealing. The decrease in resistivity was mainly attributed to the increase in Hall mobility rather than carrier concentration. As a Cr buffer layer was inserted, the film resistivity decreased by 32% to 5.41 x 10(-3) Omega cm while the energy band gap increased from 3.252 to 3.291 eV in comparison with that of the film deposited without the buffer layer. When the Cr-buffered films were annealed in a vacuum, the structural, electrical, and optical properties were improved with increasing annealing temperature. At an annealing temperature of 500 degrees C, the grain size, resistivity, and energy band gap attained the optimal values of 28.12 nm, 3.37 x 10(-3) Omega cm and 3.357 eV, respectively. The average transmittance of TZO films in the visible region was between 75% and 84%, and it decreased with increase in the grain size. The decrease in transmittance is attributed to an increase in surface roughness due to the three-dimensional island grain growth during thermal annealing. (c) 2012 Elsevier B.V. All rights reserved.