Browsing by Author "Jeng, Yeau-Ren"

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Heat Transfer and Flow Pattern Characteristics for HFE-7100 Within Microchannel Heat Sinks
(2011)
Yang, Kai-Shing
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Jeng, Yeau-Ren
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Huang, Chun-Min
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Wang, Chi-Chuan
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機械工程學系
This study investigates the heat transfer characteristics and flow pattern for the dielectric fluid HFE-7100 within multiport microchannel heat sinks with hydraulic diameters of 480 m and 790 m. The test results indicate that the heat transfer coefficient for the smaller channel is generally higher than that of the larger channel. It is found that the heat transfer coefficients are roughly independent of heat flux and vapor quality for a modest mass flux ranging from 200 to 400 kg m-2 s-1 at a channel size of 480 m and there is a noticeable increase of heat transfer coefficient with heat flux for hydraulic diameters of 790 m. The difference arises from flow pattern. However, for a smaller mass flux of 100 kg m-2 s-1, the presence of flow reversal at an elevated heat flux for hydraulic diameters of 480 m led to an appreciable drop of heat transfer coefficient. For a larger channel size of 790 m, though the flow reversal is not observed at a larger heat flux, some local early partial dryout still occurs to offset the heat flux contribution and results in an unconceivable influence of heat flux. The measured heat transfer coefficients for hydraulic diameters of 790 m are well predicted by the Cooper correlation. However, the Cooper correlation considerably underpredicts the test data by 35-85% for hydraulic diameters of 480 m. The influence of mass flux on the heat transfer coefficient is quite small for both channels.
Nanoindentation characterization of GaN epilayers on A-plane sapphire substrates
(2010-03-15)
Lin, Meng-Hung
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Wen, Hua-Chiang
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Huang, Chih-Yung
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Jeng, Yeau-Ren
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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
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Jeng, Yeau-Ren
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Yau, Wei-Hung
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Wu, Kuan-Te
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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 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.
Using nanoindentation and cathodoluminescence to identify the bundled effect of gallium nitride grown by PA-MBE
(2017-02-05)
Wen, Hua-Chiang
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Chou, Wu-Ching
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Chiang, Tun-Yuan
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Jeng, Yeau-Ren
;
Fan, Wen-Chung
We performed cathodoluminescence (CL) investigations on GaN NCs grown using molecular beam epitaxy. Bundled GaN was used to form NCs that were deposited onto commercial sapphire templates. The structures of the bundled NCs were analyzed using nanoindentation. The samples were grown with a T-G of 700, 800, and 850 degrees C, and the H values were 7.4 +/- 0.2 and 6.4 +/- 0.2 GPa; the E values were 308.4 +/- 4.3, 296.4 +/- 3.8, and 75.5 +/- 1.4 GPa, respectively. It is suspected that the discrepancies of the mechanical parameters obtained by various indentation methods are partially a result of the stress distribution inherent in the different orientations on the sapphire substrate. A scanning electron microscopy (SEM) system equipped with CL allows the direct comparison of SEM images and CL maps, captured from exactly the same area of the samples. In addition to the SEM and CL images, photoluminescence spectroscopy (PL) profiling was obtained by collecting the 20 K PL spectra at the samples. The PL profiling enables the distinguishing of the emissions by the 5 meV of the blueshift from 3.440 to 3.445 eV due to localization effects. The bundled GaN NCs resulted from the (0002) reflection at 34.6 degrees for a wurtzite structure and a raised intensity difference when the TG was increased from 700 to 850 degrees C. The crystal texture of the GaN can influence the mechanical properties at different TG stages. (C) 2016 Elsevier B.V. All rights reserved.
Using nanoindentation to investigate the temperature cycling of Sn-37Pb solders
(2017-11-01)
Wen, Hua-Chiang
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Chou, Wu-Ching
;
Lin, Po-Chen
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Jeng, Yeau-Ren
;
Chen, Chien-Chang
Using nanoindentation and energy dispersive X-ray spectrometry (EDS), we have conducted an investigation into corner failures to elucidate not only the nanomechanical properties of Sn-37Pb solder balls but also the effects of temperature cycling tests (TCTs). We found that the hardness of Sn-37Pb solder balls was greater in central locations [1.18 +/- 0.05 GPa for room-temperature (RT) sample; 1.3 +/- 0.05 GPa for TCT sample], but had standard values in corner locations (>0.2 +/- 0.02 GPa). The modulus increased after the TCTs. Nevertheless, the mechanical properties were closely related to the average area of the alpha-Pb phase. The average area of the Pb-rich region was more stable after the TCTs than that of the RT sample, due to the enhanced mechanical properties of the Sn-37Pb solder, suggesting good reliability. From an analysis of average areas in the RT sample, it appears that the Pb-rich solid solution that formed led to weak Sn-Pb bonds near the corner locations. Electron back scattered diffraction measurements revealed that grains with grain boundaries formed as a result of accelerated TCT cycling. We conclude that Sn-Pb recrystallization was initiated and propagated after the TCTs, followed by propagation to the interfacial region. (C) 2017 Published by Elsevier Ltd.