Browsing by Author "Wen, Hua-Chiang"

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A study of carbon nanotubes/biodegradable plastic polylactic acid composites
(2008-06-05)
Chiu, Wei-Ming
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Chang, You-An
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Kuo, Hsan-Yuan
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Lin, Meng-Hung
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Wen, Hua-Chiang
Fabrication process was successfully used to embed carbon nanotubes (CNTs) in a polylactic acid (PLA) matrix, forming a composite nanostructure. For the composites, nanoindentation is often used to characterize their mechanical properties (e.g., hardness and Young's moduli). In this experiment, the varied concentrations of CNTs in PLA were analyzed in their mechanical performance. The distribution and conformation of CNTs in the PLA were studied by X-ray diffraction. Then, electrical characterization was performed by four-probe method. Thermal properties were checked by TGA and DSC. Furthermore, the CNTs/PLA nanocomposites were observed by SEM. According to the experimental result, purified CNTs showed better dispersing and properties in the CNTs PLA nanocomposites. (C) 2008 Wiley Periodicals, Inc.
Cathodoluminescence study of defects in thermal treatment of zinc titanate thin films deposited by a cosputtering process
(2018-05-01)
Chiang, Tun-Yuan
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Tsai, Chien-Huang
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Huang, Ming-Chao
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Wen, Hua-Chiang
;
Chou, Wu-Ching
The effects of thermal treatment of polycrystalline ZnO-TiO2 systems on their luminescence emission and phase properties were investigated using ex situ cathodoluminescence and back-scattering electron microscopy. The main features of the spectrum are a blue band at 2.75 eV for the phase of TiO and a complex visible band at 2.18 eV for the phase of ZnO, whose peak intensity depends on the annealing temperature. The spectrum intensity is dominated by the ZnO phase when annealing temperature was 720 degrees C, which is attributed to abnormal grain growth. Competition is observed between the broad band peaked at 2.18 eV and visible band peaked at 2.75 eV as the annealing temperature changed (820 degrees C-920 degrees C). The cathodoluminescence density is gradually governed by the TiO2 phase, and the emission in polychromatic and monochromatic imaging is stronger equally at 920 degrees C. The nucleation of the TiO2 and ZnO grains is present in the backscattering electron images as well.
Characteristics of ZnO thin films prepared by radio frequency magnetron sputtering
(2008-03-01)
Yang, Ping-Feng
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Wen, Hua-Chiang
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Jian, Sheng-Rui
;
Lai, Yi-Shao
;
Wu, Sean
We investigated in this study structural and nanomechanical properties of zinc oxide (ZnO) thin films deposited onto Langasite substrates at 200 degrees C through radio frequency magnetron sputtering with an radio frequency power at 200 W in an O(2)/Ar gas mixture for different deposition time at 1, 2, and 3 h. Surface morphologies and crystalline structural characteristics were examined using X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The deposited film featured a polycrystalline nature, with (100), (002), and (101) peaks of hexagonal zinc oxide at 31.75 degrees, 34.35 degrees, and 36.31 degrees. As the deposition time increased, the ZnO film became predominantly oriented along the c-axis (002) and the surface roughness decreased. Through Berkovich nanoindentation following a continuous stiffness measurement technique, the hardness and Young's modulus of ZnO thin films increased as the deposition time increased, with the best results being obtained for the deposition time of 3 h. In addition, surface acoustic wave properties of ZnO thin films were also presented. (C) 2007 Elsevier Ltd. All rights reserved.
Characterizations of ZnO thin films deposited onto langasite substrates by r.f. magnetron sputtering
(2007)
Yang, Ping-Feng
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Wen, Hua-Chiang
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Jian, Sheng-Rui
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Lail, Yi-Shao
;
Wu, Sean
We investigated in this study structural and nanomechanical properties of zinc oxide (ZnO) thin films deposited onto langasite substrates at 200 degrees C through r.f. magnetron sputtering with an r.f. power at 200 W in an O2/Ar gas mixture for different deposition time at 1, 2, and 3 h. Surface morphologies and crystalline structural characteristics were examined using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The deposited film featured a polycrystalline nature, with (100), (002), and (101) peaks of hexagonal ZnO at 31.75 degrees, 34.35 degrees, and 36.31 degrees. As the deposition time increased, the ZnO film became predominantly oriented along the c-axis (002) and the surface roughness decreased. Through Berkovich nanoindentation following a continuous stiffness measurement (CSM) technique, the hardness and Young\'s modulus of the ZnO thin films increased as the deposition time increased, with the best results being obtained for the deposition time of 3 h.
Effect of annealing treatment and nanomechanical properties for multilayer Si(0.8)Ge(0.2)-Si films
(2010-06-01)
He, Bo-Ching
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Wen, Hua-Chiang
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Lin, Meng-Hung
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Lai, Yi-Shao
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Wu, Wen-Fa
Multilayered silicon-germanium (SiGe) films consisting of alternating sublayers with different mechanical properties have been epitaxially deposited by an ultra-high vacuum chemical vapor deposition (UHV/CVD) system. We report engineering of the mechanical properties of SiGe multilayer films by a commercial nanoindenter. From annealing treatment, it consists of an ex situ thermal treatments in furnace (600 degrees C) and rapid thermal annealing (800 degrees C) system. Subsequent roughness and microstructure of SiGe multilayer films were characterized by means of atomic force microscope (AFM) and transmission electron microscopy (TEM). The annealing treatment not only produced misfit dislocations as a significant role in the critical pile-up event but also promoted hardness. The hardness of the films increased slightly and then gradually achieved a maximum value (from 12.6 +/- 0 4 GPa to 14.2 +/- 0.7 GPa) with increasing annealing temperature. This may be due to the relaxation effect from thermal annealing and is potential to provide the reliability behaviours to design periodical SiGe multilayer structure in further. (C) 2010 Published by Elsevier Ltd
Effect of microstructure on the nanomechanical properties of Zn(1-x)Cd(x)Se alloys
(2010-01-15)
Wen, Hua-Chiang
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Yang, Chu-Shou
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Chou, Wu-Ching
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電子物理學系
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Department of Electrophysics
We present a study of the nanoindentation behavior of Zn(1-x)Cd(x)Se epilayers grown using molecular beam epitaxy; the surface roughness, microstructure, and crystallinity were analyzed using atomic force microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction; the hardness H and elastic modulus E were studied using nanoindentation techniques. We found that these highly crystalline materials possessed no stacking faults or twins in their microstructures. We observed a very marked increase in the value of H and a significant decrease in the value of E upon increasing the concentration of Cd, presumably because of an increase in the stiffness of the CdSe bond relative to that of the ZnSe bond. We observed a corresponding shrinkage of the contact-induced damage area for those films having a small grain size and a higher value of H. It appears that resistance against contact-induced damage requires a higher Cd concentration. (C) 2009 Elsevier B.V. All rights reserved.
Effect of microstructure on the nanomechanical properties of Zn1-xCdxSe alloys
(2010-01-15)
Wen, Hua-Chiang
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Yang, Chu-Shou
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Chou, Wu-Ching
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電子物理學系
;
Department of Electrophysics
We present a study of the nanoindentation behavior of Zn1-xCdxSe epilayers grown using molecular beam epitaxy; the surface roughness, microstructure, and crystallinity were analyzed using atomic force microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction; the hardness H and elastic modulus E were studied using nanoindentation techniques. We found that these highly crystalline materials possessed no stacking faults or twins in their microstructures. We observed a very marked increase in the value of H and a significant decrease in the value of E upon increasing the concentration of Cd, presumably because of an increase in the stiffness of the CdSe bond relative to that of the ZnSe bond. We observed a corresponding shrinkage of the contact-induced damage area for those films having a small grain size and a higher value of H. It appears that resistance against contact-induced damage requires a higher Cd concentration. (C) 2009 Elsevier B.V. All rights reserved.
Effect of repetition nanoindentation of GaN epilayers on a-axis sapphire substrates
(2011-05-01)
Lin, Meng-Hung
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Wen, Hua-Chiang
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Chang, Zue-Chin
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Wu, Shyh-Chi
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Wu, Wen-Fa
In this work, gallium nitride (GaN) epilayers were deposited on a-axis sapphire substrate by means of metal organic chemical vapor deposition (MOCVD). Berkovich nanoindentation was used to explore the repetition pressure-induced impairment of the GaN film. The observation of load-displacement vs stress-strain curves concludes that basal slip is implicated in the deformation on the A plane GaN. The increase in the hardness (H) and elasticmodulus (E) was determined from cyclic nanoindentation, and resulted in a crack due to the formation of incipient slip bands and/or the to-and-fro motion of mobile dislocation. It is indicated that the generation of individual dislocation and residual deformation of the GaN films are showed by CL mapping analysis. From the morphological studies, it is revealed that the crack was found by means of atomic force microscope (AFM) technique at nine loading/reloading cycles even after the indentation beyond the critical depth on the residual indentation impression. Copyright (C) 2010 John Wiley & Sons, Ltd.
Effect of strain relaxation of oxidation-treated SiGe epitaxial thin films and its nanomechanical characteristics
(2010-03-01)
He, Bo-Ching
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Wen, Hua-Chiang
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Chinag, Tun-Yuan
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Chang, Zue-Chin
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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.
Evaluating nanotribological behavior of annealing Si(0.8)Ge(0.2)/Si films
(2011-12-01)
Wu, Ming-Jhang
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Wen, Hua-Chiang
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Wu, Shyh-Chi
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Yang, Ping-Feng
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Lai, Yi-Shao
In this study, the SiGe epilayers were created on silicon substrate by using ultra-high vacuum chemical vapor deposition (UHV/CVD) and followed by annealing procedures. The frictional behaviors of SiGe epilayers were subjected to nanoscratch techniques under a ramping load. Damage caused by scratching was examined by atomic force microscopy (AFM); the results showed that the pile-up phenomena were significant on both sides of the scratch in the case of SiGe epilayers, suggesting that the dynamic deformation behavior was dominated by cracking as ploughing occurred during scratching. In addition, the SiGe epilayers films with different annealed conditions exhibited the decrease in coefficient of friction (COF), indicating the higher shear resistance exist in annealed SiGe epilayers, which probably affect the film uniformity and device yield under IC process integration. (C) 2011 Elsevier Ltd. All rights reserved.
Evaluating nanotribological behavior of annealing Si0.8Ge0.2/Si films
(2011-12-01)
Wu, Ming-Jhang
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Wen, Hua-Chiang
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Wu, Shyh-Chi
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Yang, Ping-Feng
;
Lai, Yi-Shao
In this study, the SiGe epilayers were created on silicon substrate by using ultra-high vacuum chemical vapor deposition (UHV/CVD) and followed by annealing procedures. The frictional behaviors of SiGe epilayers were subjected to nanoscratch techniques under a ramping load. Damage caused by scratching was examined by atomic force microscopy (AFM); the results showed that the pile-up phenomena were significant on both sides of the scratch in the case of SiGe epilayers, suggesting that the dynamic deformation behavior was dominated by cracking as ploughing occurred during scratching. In addition, the SiGe epilayers films with different annealed conditions exhibited the decrease in coefficient of friction (COF), indicating the higher shear resistance exist in annealed SiGe epilayers, which probably affect the film uniformity and device yield under IC process integration. (C) 2011 Elsevier Ltd. All rights reserved.
Evaluating the abrasive wear of Zn(1-x)Mn(x)O heteroepitaxial layers using a nanoscratch technique
(2010-08-01)
Chang, Yu-Ming
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Wen, Hua-Chiang
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Yang, Chu-Shou
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Lian, Derming
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Tsai, Chien-Huang
In this study, we used nanoscratch techniques under a ramping load to evaluate the abrasive wear of Zn(1-x)Mn(x)O epilayers (0 <= x <= 0.16) grown through molecular beam epitaxy (MBE) on sapphire substrates. We analyzed the surface roughness and damage using atomic force microscopy (AFM) and nano-indenter techniques. The scratched surfaces of the Zn(1-x)Mn(x)O epilayers were significantly different for the various Mn compositions. AFM imaging of the Zn(1-x)Mn(x)O films revealed that pileup phenomena were important on both sides of each scratch. During the scratching process, we found that cracking dominated in the case of Zn(1-x)Mn(x)O films while ploughing; also we observed lower values of the coefficient of friction and shallower penetration depths for the films upon increasing the Mn content (x) from 0 to 0.16, suggesting that higher Mn contents provided the Zn(1-x)Mn(x)O epilayers with higher shear resistances, enhanced by the presence of MnO bonds. (C) 2010 Elsevier Ltd. All rights reserved.
Evaluating the abrasive wear of Zn1-xMnxO heteroepitaxial layers using a nanoscratch technique
(2010-08-01)
Chang, Yu-Ming
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Wen, Hua-Chiang
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Yang, Chu-Shou
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Lian, Derming
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Tsai, Chien-Huang
In this study, we used nanoscratch techniques under a ramping load to evaluate the abrasive wear of Zn1-xMnxO epilayers (0 <= x <= 0.16) grown through molecular beam epitaxy (MBE) on sapphire substrates. We analyzed the surface roughness and damage using atomic force microscopy (AFM) and nano-indenter techniques. The scratched surfaces of the Zn1-xMnxO epilayers were significantly different for the various Mn compositions. AFM imaging of the Zn1-xMnxO films revealed that pileup phenomena were important on both sides of each scratch. During the scratching process, we found that cracking dominated in the case of Zn1-xMnxO films while ploughing; also we observed lower values of the coefficient of friction and shallower penetration depths for the films upon increasing the Mn content (x) from 0 to 0.16, suggesting that higher Mn contents provided the Zn1-xMnxO epilayers with higher shear resistances, enhanced by the presence of MnO bonds. (C) 2010 Elsevier Ltd. All rights reserved.
Evaluation of the nanoindentation behaviors of SiGe epitaxial layer on Si substrate
(2010-01-01)
He, Bo-Ching
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Cheng, Chun-Hu
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Wen, Hua-Chiang
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Lai, Yi-Shao
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Yang, Ping-Feng
In this paper, ultra-high vacuum chemical vapor deposition (UHV/CVD) was employed to synthesize silicon-germanium (SiGe), and sequence to endure annealing treatment. Morphological characterization, roughness, and microstructural morphology were observed by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The elements distribution, crystallographic, and nanomechanical behavior were carried out using energy-dispersive Xray spectroscopy (EDS) mapping technique, X-ray diffraction (XRD), and nanoindentation technique. The annealing treated SiGe leads to the 2D germanium segregation on the surface. The phenomenon is interpreted in terms of dislocation-induced structural changes in annealing treatment, Thus, the dislocation propagation in the microstructure was observed. Subsequently hardness and elastic modulus were increased because of a comparatively unstable microstructure after annealing treatment. (C) 2009 Elsevier Ltd. All rights reserved.
Field emission characteristics of carbon nanotubes post-treated with high-density Ar plasma
(2010-01-15)
Wang, Wen-Pin
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Wen, Hua-Chiang
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Jian, Sheng-Rui
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Cheng, Huy-Zu
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Jang, Jason Shian-Ching
The field emission characteristics of carbon nanotubes (CNTs) grown by thermal chemical vapor deposition (CVD) and subsequently surface treated by high-density Ar plasma in an inductively coupled plasma reactive ion etching (ICP-RIE) with the various plasma powers were measured. Results indicate that, after treated by Ar plasma with power between 250 and 500 W, the emission current density of the CNTs is enhanced by nearly two orders of magnitude (increased from 0.65 to 48 mA/cm(2)) as compared to that of the as-grown ones. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to investigate the structural features relevant to the modified field emission properties of CNTs. The SEM images of CNTs subjected to a 500 W Ar plasma treatment exhibit obvious damages to the CNTs. Nevertheless, the turn-on fields decreased from 3.6 to 2.2V/mu m, indicating a remarkable field emission enhancement. Our results further suggest that the primary effect of Ar plasma treatment might be to modify the geometrical structures of the local emission region in CNTs. In any case, the Ar plasma treatment appears to be an efficient method to enhance the site density for electron emission and, hence markedly improving the electric characteristics of the CNTs. (C) 2009 Elsevier B.V. All rights reserved.
Fracture responses of microstructures of electron beam-welded D6AC
(2012-07-20)
Wu, Shyh-Chi
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Wen, Hua-Chiang
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Wu, Ming-Jhang
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Chou, Chang-Pin
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機械工程學系
In this study, D6AC steel was produced from flow forming (wall thickness reduction: 67%) and then it was subjected to electron beam welding and tempering treated. We characterized the specimens in terms of their microstructures and nanotribological properties. After tempering treatment at 315 degrees C, the yield strength increased from 381 to 1334 MPa and the percentage elongation increased remarkably from 0.5 to 7.8%. We performed these mechanical studies for the samples subjected to each set of experimental conditions, and determined the tribological characteristics from the heat-affected zone and the fusion zone. Lower degrees of adhesion reflected the presence of interlinks and rearrangements of indenter tip at lateral force that have been responsible for fluctuations in the coefficients of friction. (C) 2012 Elsevier Ltd. All rights reserved.
Luminescence properties of mechanically nanoindented ZnSe
(2011-05-01)
Yau, Wei-Hung
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Tseng, Pai-Chung
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Wen, Hua-Chiang
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Tsai, Chien-Huang
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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.
Mechanical properties of InGaN thin films deposited by metal-organic chemical vapor deposition
(2008-06-15)
Jian, Sheng-Rui
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Jang, Jason Shian-Ching
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Lai, Yi-Shao
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Yang, Ping-Feng
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Yang, Chu-Shou
We report in this study characteristics of InGaN thin films developed by metal-organic chemical vapor deposition (MOCVD) at various growth temperatures. The effect of deposition temperatures on microstructures and mechanical properties are examined using X-ray diffraction (XRD), scanning probe microscopy (SPM), and nanoindentation techniques. The XRD analysis shows no evidence of phase separation for InGaN thin films. The SPM micrographs indicate that the films have relatively smooth surfaces. Hardness and Young's modulus of InGaN thin films vary according to the deposition temperature. As the deposition temperature increases from 730 to 790 degrees C, the grain size increases from 28 to 52 nm. Hardness for InGaN thin films dropped from 13.8 to 17.6 GPa in accordance with the increase of the grain size. By fitting experimental data with the Hall-Petch equation, a probable lattice friction stress of 3.48 GPa and Hall-Petch constant of 73.15 GPa nm(1/2) are obtained. (C) 2007 Elsevier B.V. All rights reserved.
Mechanical Research of Carbon Nanotubes/PMMA Composite Films
(2008-12-01)
Luo, Jen-Tsung
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Wen, Hua-Chiang
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Wu, Wen-Fa
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Chou, Chang-Pin
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機械工程學系
Carbon nanotubes (CNTs) are one of the best candidates for reinforcing the next generation of high-performance nanocomposites owing to their excellent mechanical properties. In this study, CNTs were dispersed in poly-methymethacrylate (PMMA) gel to enhance its mechanical strength. CNTs/PMMA composite films were fabricated using direct mixing and sonication. FTIR was utilized to observe the chemical structure and functional groups of the material components. The morphological feature and phase structure were observed via scanning electron microscope. A nanoindenter system was also applied to investigate the mechanical properties of composite films by a conventional method. CNTs were chemically treated by immersing them in acidic solutions to ensure extensive dispersion in the surrounding matrix. Most of the CNTs were dispersed uniformly therein. The effective dispersion of CNTs improves the mechanical performance of the composite film, wheras the poor dispersion reduces the performance. The solvent, solubility and attractive intermolecular forces, such as hydrogen bonds and Van Der Waal forces affect the dispersion of the CNTs. The carbonyl group, which was found on the composite film, contributed to the formation of a covalent bond between PMMA and the CNTs. The mechanical interaction between CNTs and the polymer was very complex. It was also governed by the interface interaction. The mechanical properties of the composite films improved as the concentration of CNTs increased. POLYM. COMPOS., 29:1285-1290, 2008. (C) 2008 Society of Plastics Engineers
Mesoporous silica reinforced by silica nanoparticles to enhance mechanical performance
(2007-01-15)
Luo, Jen-Tsung
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Wen, Hua-Chiang
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Chang, Yu-Ming
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Wu, Wen-Fa
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Chou, Chang-Pin
Silica nanoparticle/mesoporous silica composite films were prepared by direct mixing with mechanical stirring and thermal imidization. The structural morphology was elucidated by scanning electron microscopy and the surface of the film was imaged by atomic force microscopy. The functional groups and desorption process of the films were elucidated by Fourier transform infrared spectroscopy and thermal desorption spectroscopy. The mechanical properties were investigated using a nanoindenter system. The gel matrix and the filler are very compatible because they have similar molecular content. The composite films had a higher mechanical strength than pure porous silica film. Their strength is related to the silica nanoparticle content. The interfacial compatibility, dispersion effect, and interfacial strength also affect the mechanical strength of composite films. (c) 2006 Elsevier Inc. All rights reserved.