Browsing by Author "Yau, Wei-Hung"

Now showing 1 - 11 of 11

Effect of strain relaxation of oxidation-treated SiGe epitaxial thin films and its nanomechanical characteristics
(2010-03-01)
He, Bo-Ching
;
Wen, Hua-Chiang
;
Chinag, Tun-Yuan
;
Chang, Zue-Chin
;
Lian, Derming
In this study, we examined the effect of high-temperature oxidation treatment on the SiGe epitaxial thin films deposited on Si substrates. The X-ray diffraction (XRD), atomic force microscopy (AFM), and nanoindentation techniques were employed to investigate the crystallographic structure, surface roughness, and hardness (H) of the SiGe thin films, respectively. The high-temperature oxidation treatment led to Ge pileup at the surface of the SiGe thin films. In addition, strain relaxation occurred through the propagation of misfit dislocations and could be observed through the cross-hatch pattern (800-900 degrees C) and SiGe islands (1000 degrees C) at the surface of the SiGe thin films. Subsequent hardness (H) measurement on the SiGe thin films by continuous penetration depth method indicated that the phenomenon of Ge pileup caused a slightly reduced H (below 50 nm penetration depth), while relaxation-induced defects caused an enhanced H (above 50 nm penetration depth). This reveals the influence of composition and defects on the structure strength of high-temperature oxidation-treated SiGe thin films. (C) 2009 Elsevier B.V. All rights reserved.
Luminescence properties of mechanically nanoindented ZnSe
(2011-05-01)
Yau, Wei-Hung
;
Tseng, Pai-Chung
;
Wen, Hua-Chiang
;
Tsai, Chien-Huang
;
Chou, Wu-Ching
In this study, we used cathodoluminescence (CL) spectroscopy to examine the CL emissions of zinc selenide (ZnSe) single crystals that had been subjected to Berkovich nanoindentation. The CL spectra of the ZnSe exhibited both impurity emission peaks (1.8-2.4 eV band) and near-bandgap emission peaks (2.68 eV). Although CL emissions were generated during four unloading/reloading cycles, the decreased intensity of the impurity emission can be explained in terms of extended dislocation nucleation and propagation during nanoindentation. The resultant dislocation and microcracks were visualized using CL mapping and transmission electron microscopy. We suspect that the formation of a hysteresis loop during the four unloading/reloading cycles was due, in part, to massive dislocation activities induced by the indenter. (C) 2011 Elsevier Ltd. All rights reserved.
Nanoindentation characterization of GaN epilayers on A-plane sapphire substrates
(2010-03-15)
Lin, Meng-Hung
;
Wen, Hua-Chiang
;
Huang, Chih-Yung
;
Jeng, Yeau-Ren
;
Yau, Wei-Hung
Gallium nitride (GaN) epilayers was deposited on a-axis sapphire substrate by means of metal-organic chemical vapor deposition (MOCVD) method. The GaN epilayers has been investigated in their repetition pressure-induced impairment events from nanoindentation technique and, the relative deformation effect was observed from atomic force microscopy (AFM). From the morphological studies, it is revealed that none of crack and particle was found even after the indentation beyond the critical depth on the residual indentation impression. The 'pop-in' event was explained by the interaction of the deformed region, produced by the indenter tip, with the inner threading dislocations in the GaN films. Pop-in events indicate the generation and motion of individual dislocation, which is measured under critical depth and, no residual deformation of the GaN films is observed. (C) 2009 Elsevier B. V. All rights reserved.
Nanoindentation response of zinc titanate thin films deposited by co-sputtering process
(2012-07-01)
Wu, Shyh-Chi
;
Jeng, Yeau-Ren
;
Yau, Wei-Hung
;
Wu, Kuan-Te
;
Tsai, Chien-Huang
In this study, ZnTiO3 films were grown by radio frequency magnetron co-sputtering using a sintered ceramic target on silicon substrates, we used nanoindenter techniques under a CSM mode to evaluate the hardness (H) and elastic modulus (E) of the films after annealing in temperature range of 520-820 degrees C. The measured values of hardness and elastic moduli of the ZnTiO3 films were in the range from 8.5 +/- 0.4 to 5.6 +/- 0.4 GPa and from 171 +/- 2.3 to 155 +/- 2.5 GPa, respectively. It is evident that an increase in the roughness due to high annealing temperature using atomic force microscopy. The XRD patterns were observed that as-deposited films are mainly amorphous, however, the hexagonal ZnTiO3 phase was observed with the ZnTiO3 (1 0 4), (1 1 0), (1 1 6), and (2 1 4) peaks from 620 to 820 degrees C, indicating that there is highly (1 0 4)-oriented ZnTiO3 on the silicon substrate. The X-ray photoelectron spectroscopy core level analysis of the ZnTiO3 films have been measured for O 1s that can be attributed the weaker bonds and lower resistance at the film based on the higher annealed temperature. The H, M, Rms, and Ra were altered due to the grain growth and recovery to result in a relax crystallinity at ZnTiO3 films. (C) 2012 Elsevier B. V. All rights reserved.
Nanoscratch study of Zn(1-x)Mn(x)O heteroepitaxial layers
(2010-10-15)
Chang, Yu-Ming
;
Chang, Zue-Chin
;
Lian, Derming
;
Yang, Chu-Shou
;
Yau, Wei-Hung
We investigated the nanotribological properties of Zn(1-x)Mn(x)O epilayers (0 <= x <= 0.16) grown by molecular beam epitaxy (MBE) on sapphire substrates. The surface roughness and friction coefficient (mu) were analyzed by means of atomic force microscopy (AFM) and hysitron triboscope nanoindenter techniques. The nanoscratch system gave the mu value of the films ranging from 0.17 to 0.07 and the penetration depth value ranging 294-200nm when the Mn content was increased from x = 0 to 0.16. The results strongly indicate that the scratch wear depth under constant load shows that higher Mn content leads to Zn(1-x)Mn(x)O epilayers with higher shear resistance, which enhances the Mn-O bond. These findings reveal that the role of Mn content on the growth of Zn(1-x)Mn(x)O epilayers can be identified by their nanotribological behavior. (C) 2010 Elsevier B.V. All rights reserved.
Nanoscratch study of Zn1-xMnxO heteroepitaxial layers
(2010-10-15)
Chang, Yu-Ming
;
Chang, Zue-Chin
;
Lian, Derming
;
Yang, Chu-Shou
;
Yau, Wei-Hung
We investigated the nanotribological properties of Zn1-xMnxO epilayers (0 <= x <= 0.16) grown by molecular beam epitaxy (MBE) on sapphire substrates. The surface roughness and friction coefficient (mu) were analyzed by means of atomic force microscopy (AFM) and hysitron triboscope nanoindenter techniques. The nanoscratch system gave the mu value of the films ranging from 0.17 to 0.07 and the penetration depth value ranging 294-200nm when the Mn content was increased from x = 0 to 0.16. The results strongly indicate that the scratch wear depth under constant load shows that higher Mn content leads to Zn1-xMnxO epilayers with higher shear resistance, which enhances the Mn-O bond. These findings reveal that the role of Mn content on the growth of Zn1-xMnxO epilayers can be identified by their nanotribological behavior. (C) 2010 Elsevier B.V. All rights reserved.
Nanotribological behavior of thermal treatment of zinc titanate thin films
(2012-10-01)
Wu, Shyh-Chi
;
Yau, Wei-Hung
;
Tsai, Chien-Huang
;
Chou, Chang-Pin
;
機械工程學系
We present a study of the nanotribological behavior of ZnTiO3 films; the surface morphology, stoichiometry, and friction (mu) were analyzed using atomic force microscopy, X-ray photoelectron spectroscopy, and nanoscratch system. It is confirmed that the measured values of H and mu of the ZnTiO3 films were in the range from 8.5?+/-?0.4 to 5.6?+/-?0.4 GPa and from 0.164 to 0.226, respectively. It is suggested that the hexagonal ZnTiO3 decomposes into cubic Zn2TiO4 and rutile TiO2 based on the thermal treatment; the H, mu, and RMS were changed owing to the grain growth and recovery that results in a relax crystallinity of ZnTiO3 films. From X-ray photoelectron spectroscopy measured, core levels of O 1 can attribute the weaker bonds as well as lower resistance after thermal treatment. The XRD patterns showed that as-deposited films are mainly amorphous; however, the hexagonal ZnTiO3 phase was observed with the ZnTiO3 (104), (110), (116), and (214) peaks from 620 to 820 degrees C, indicating that there is highly (104)-oriented ZnTiO3 on the silicon substrate. Copyright (c) 2012 John Wiley & Sons, Ltd.
Nanotribological behavior of ZnO films prepared by atomic layer deposition
(2014-03-01)
Wang, Wun-Kai
;
Wen, Hua-Chiang
;
Cheng, Chun-Hu
;
Chou, Wu-Ching
;
Yau, Wei-Hung
We used atomic layer deposition to form ZnO thin-film coatings on Si substrates and then evaluate the effect of pile-up using the nanoscratch technique under a ramped mode. The wear volume decreased with increasing annealing temperature from room temperature to 400 degrees C for a given load. Elastic-to-plastic deformation occurred during sliding scratch processing between the groove and film for loading penetration of 30 nm. The onset of non-elastic behavior and greater contact pressure were evident for loading penetration of 150 nm; thus, full plastic deformation occurred as a result of a substrate effect. We suspect that elastic-plastic failure events were related to edge bulging between the groove and film, with elastic-plastic deformation attributable to adhesion discontinuities and/or cohesion failure of the ZnO films. (C) 2013 Elsevier Ltd. All rights reserved.
Nanotribological properties of ALD-processed bilayer TiO2/ZnO films
(2014-12-01)
Wang, Wun-Kai
;
Wen, Hua-Chiang
;
Cheng, Chun-Hu
;
Hung, Ching-Hua
;
Chou, Wu-Ching
TiO2/ZnO films grown by atomic layer deposition (ALD) demonstrated nanotribological behaviors using scratch testing. TEM profiles obtained an amorphous structure TiO2 and nanocrystalline structure ZnO, whereas the sample has significant interface between the TiO2/ZnO films. The experimental results show the relative XRD peak intensities are mainly contributed by a wurtzite oxide ZnO structure and no signal from the amorphous TiO2. With respect to tribology, increased friction causes plastic deformation between the TiO2 and ZnO films, in addition to delamination and particle loosening. The plastic deformation caused by adhesion and/or cohesion failure is reflected in the nanoscratch traces. The pile-up events at a loading penetration of 30 nm were measured at 21.8 mu N for RT, 22.4 mu N for 300 degrees C, and 36 mu N for 400 degrees C. In comparison to the other conditions, the TiO2/ZnO films annealed at 400 degrees C exhibited higher scratch resistance and friction with large debris, indicating the wear volume is reduced with increased annealing temperature and loading. (C) 2014 Elsevier Ltd. All rights reserved.
Sliding wear resistance of tempered D6ac steel
(2013-01-01)
Wu, Shyh-Chi
;
Wene, Hua-Chiang
;
Tseng, Kuang-Hung
;
Yau, Wei-Hung
;
Wu, Ming-Jhang
The aim of this study was to determine the sliding wear resistance of D6ac (tempered at room temperature, 450, or 550 degrees C) and to perform tribological responds. The obtained microstructures exhibited a heavy number of misfit dislocations from work hardening of the parent material, with the degree of disorder dislocation decreasing gradually upon increasing the temperature from 450 to 550 degrees C. XRD spectra observed that the residual austenite and/or mixed structures of ferrite with the precipitation of carbides at 550 degrees C will result in a softer state than that of the room temperature specimen. The elevated temperature affected the tribological behavior and induced in the parent material a significant surface response failure. The lateral force increased gradually up to 50 mu N in the tempered cases, due to the enhanced toughness. We suggest that the increase in the coefficients of friction upon increasing the tempering temperature from 450 to 550 degrees C resulted due to a soft ferrite phase. Slightly stable fluctuations of the values of mu appeared for the surfaces scratched at a constant load; therefore, plastic deformation occurred along the wear path. For the measured results of the D6ac from room temperature to 550 degrees C, the coefficient of friction was 0.34 +/- 0.05, 0.27 +/- 0.04, and 0.13 +/- 0.02, respectively. The experimental result also can be evidenced from tribological stressing and mechanical behavior. (C) 2012 Elsevier Ltd. All rights reserved.
Using nanoindentation and cathodoluminescence to investigate the residual stress of ZnSe
(2015-03-15)
Wen, Hua-Chiang
;
Chou, Wu-Ching
;
Yau, Wei-Hung
;
Fan, Wen-Chung
;
Lee, Ling
In this study we examined the effects of the nanoindentation-induced residual stress of single-crystalline zinc selenide (ZnSe). We employed the nanoindentation technique to evaluate the dislocation mobility of ZnSe at loading ratios of 10 and 2 mN/min, with a holding time of 120 s under a constant load. We visualized the resultant dislocation and microcracks using cathodoluminescence (CL) spectroscopy and mapping to compare the nanoindentation-induced residual stresses of the various ZnSe samples. CL mapping revealed massive dislocation activities during the loading process. The dislocations played roles as nonradiative recombination centers that quenched the local CL intensity. Transmission electron microscopy also revealed the effects of nanoindentation-induced residual stress. To obtain insight into the influence of the residual stress and to determine the dislocation mobilities for ZnSe films, it was essential to monitor the quenching effect of nonradiative recombination centers as a function of CL mapping. (C) 2014 Elsevier B.V. All rights reserved.