Browsing by Author "Lin, Meng-Hung"

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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
;
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.
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
;
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 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
;
Wu, Shyh-Chi
;
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.
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
;
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.
Formation of size-tunable dandelion-like hierarchical rutile titania nanospheres for dye-sensitized solar cells
(2013)
Lan, Chi-Ming
;
Liu, Shang-En
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Shiu, Jia-Wei
;
Hu, Jyun-Yu
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Lin, Meng-Hung
A sol-gel method with a modified solvent comprising of three simple steps under low-temperature conditions was used to synthesize mono-disperse rutile TiO2 nanospheres with dandelion-like hierarchical morphology (DHRS) as a light-scattering layer for dye-sensitized solar cells (DSSC). 1,2-Ethanediol (ED) served as a key retardation agent in the second step at 25 degrees C to slow the hydrolysis and condensation of the TiCl4 aqueous solution prepared in the first step at 0 degrees C; the subsequent nucleation of a rutile type phase occurred homogeneously in the third step at 70 degrees C to generate the rutile TiO2 nanospheres with highly uniform sizes. The spherical sizes of DHRS were well controlled with the volume ratios of the ED-water solvent mixture in the second step, for which the DHRS of diameter 650-200 nm were produced from the solvent system containing 5-25% ED. A detailed mechanism is presented to rationalize the formation of nanospheres of uniform size in six steps: 1) hydration and hydrolysis, 2) hydrolysis and retardation, 3) hydrolysis and condensation, 4) homogeneous nucleation, 5) aggregation and growth of rod-like crystals and 6) DHRS formation. The DSSC device with a scattering layer made of DHRS (size similar to 300 nm) performed comparably to that with a scattering layer made of a commercially available TiO2 paste, making this nano-material a cost-effective alternative for future DSSC commercialization.
High-Performance Large-Scale Flexible Dye-Sensitized Solar Cells Based on Anodic TiO2 Nanotube Arrays
(2013-10-01)
Jen, Hsiu-Ping
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Lin, Meng-Hung
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Li, Lu-Lin
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Wu, Hui-Ping
;
Huang, Wei-Kai
A simple strategy to fabricate flexible dye-sensitized solar cells involves the use of photoanodes based on TiO2 nanotube (TNT) arrays with rear illumination. The TNT films (tube length similar to 35 mu m) were produced via anodization, and sensitized with N719 dye for photovoltaic characterization. Pt counter electrodes of two types were used: a conventional FTO/glass substrate for a device of rigid type and an ITO/PEN substrate for a device of flexible type. These DSSC devices were fabricated into either a single-cell structure (active area 3.6 X 0.5 cm(2)) or a parallel module containing three single cells (total active area 5.4 cm(2)). The flexible devices exhibit remarkable performance with efficiencies eta = 5.40 % (single cell) and 4.77 % (parallel module) of power conversion, which outperformed their rigid counterparts with eta = 4.87 % (single cell) and 4.50 % (parallel model) under standard one-sun irradiation. The flexible device had a greater efficiency of conversion of incident photons to current and a broader spectral range than the rigid device; a thinner electrolyte layer for the flexible device than for the rigid device is a key factor to improve the light-harvesting ability for the TNT-DSSC device with rear illumination. Measurements of electrochemical impedance spectra show excellent catalytic activity and superior diffusion characteristics for the flexible device. This technique thus provides a new option to construct flexible photovoltaic devices with large-scale, light-weight, and cost-effective advantages for imminent applications in consumer electronics.
Nanoindentation characterization of GaN epilayers on A-plane sapphire substrates
(2010-03-15)
Lin, Meng-Hung
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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.
Nanoscratch Characterization of GaN Epilayers on c- and a-Axis Sapphire Substrates
(2010-11-01)
Lin, Meng-Hung
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Wen, Hua-Chiang
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Jeng, Yeau-Ren
;
Chou, Chang-Pin
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機械工程學系
In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN) epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM) to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (mu) and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 mu N. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.