Browsing by Author "Chen, C. Y."

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Carrier dynamics in isoelectronic ZnSe(1-x)O(x) semiconductors
(2010-07-26)
Lin, Y. C.
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Chung, H. L.
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Chou, W. C.
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Chen, W. K.
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Chang, W. H.
This study explores the effects of both Oxygen and temperature on the carrier dynamics of isoelectronic ZnSe(1-x)O(x) (x=0.027 and 0.053) semiconductors using photoluminescence (PL) and time-resolved PL spectroscopy. We find that the Kohlrausch law is highly consistent with the complex decay traces induced by isoelectronic O traps, and the mechanism of carrier recombination undergoes a complicated change from trapped to free excitons with the increase in temperature. Complex recombination processes are clarified using the relaxation model based on various decay channels. These findings are consistent with the initial fall in the stretching exponent beta followed by its monotonic increase with increasing temperature. (C) 2010 American Institute of Physics. [doi:10.1063/1.3473776]
Carrier dynamics in isoelectronic ZnSe1-xOx semiconductors
(2010-07-26)
Lin, Y. C.
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Chung, H. L.
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Chou, W. C.
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Chen, W. K.
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Chang, W. H.
This study explores the effects of both Oxygen and temperature on the carrier dynamics of isoelectronic ZnSe1-xOx (x=0.027 and 0.053) semiconductors using photoluminescence (PL) and time-resolved PL spectroscopy. We find that the Kohlrausch law is highly consistent with the complex decay traces induced by isoelectronic O traps, and the mechanism of carrier recombination undergoes a complicated change from trapped to free excitons with the increase in temperature. Complex recombination processes are clarified using the relaxation model based on various decay channels. These findings are consistent with the initial fall in the stretching exponent beta followed by its monotonic increase with increasing temperature. (C) 2010 American Institute of Physics. [doi:10.1063/1.3473776]
Designing novel lightweight, high-strength and high-plasticity Ti-x(AlCrNb)(100-x) medium-entropy alloys
(2020-02-01)
Liao, Y. C.
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Li, T. H.
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Tsai, P. H.
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Jang, J. S. C.
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Hsieh, K. C.
Due to the demand for reduced energy consumption by transportation vehicles, lighter weight high-entropy alloys (with density comparable to that of commercial Ti alloys around 4.5-5 g/cm(3)) are attracting more attention in terms of alloy design and application as structural materials. In this study, a nonequiatomic quaternary alloy system, Ti-x(AlCrNb)(100-x), was designed through the calculation of phase diagrams. Simulation results reveal that a single body-centered cubic (BCC) phase can be formed and can be stable at temperatures above 950 degrees C. Accordingly, a series of Ti-x(AlCrNb)(100-x), (x = 45-80) alloys containing a BCC structure were prepared through vacuum arc melting and rapid cooling. The designed alloys can exhibit desirable mechanical properties with high compression yield strength about 1500 MPa, high compression fracture strength about 1800 MPa and high compression plasticity more than 30% at room temperature. Moreover, the Ti65 alloy can demonstrate a tensile strength of 1200 MPa with a tensile elongation of 32%, after a homogenization treatment for 24 h. The specific compression and tensile strength can reach 0.36 and 0.24 GPa cm(3)/g.
Effects of growth interruption time on InGaN/GaN quantum dots grown by metal organic chemical vapor deposition - art. no. 612102
(2006)
Yao, H. H.
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Huang, G. S.
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Lu, T. C.
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Chen, C. Y.
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Liang, W. D.
Wide-bandgap gallium nitride (GaN) quantum dot (QD) structure is attractive because it is a zero-dimensional (0-D) confinement structure and has many unique physical characteristics. We have successfully grown self-assembled InGaN QDs structure by metal organic chemical vapor deposition. A high quality GaN/sapphire template with a flat surface and the suitable growth condition including low growth temperature and low V/III ratio were used to grow InGaN QDs structure. The density of InGaN QDs is about 4.5 x 10(10) cm(-2) with an average lateral size of 11.5 nm and an average height of 1.6 nm. The effect of the interruption growth for InGaN QDs structure was systematic studied with the growth temperature of 660 degrees C. The surface morphology and optical property was measured by atomic forced microscopy and various temperature PL, respectively. The results indicated that as increasing interruption time from 30s to 120s, QDs area occupied on the surface above the wetting layer increases from 5.2% to 7.2%, and the In composition decreases from 25% to 21%. The results were discussed by considering the influences of ad-atom desorption and diffusion effect between wetting layer and InGaN QDs structure. Our results suggest that the interruption growth during an optimum time can modify the size of InGaN QDs and extend the emission wavelength to short wavelength, and at the same time improve the QD optical quality. Using this technique was feasible for formation of multi layer InGaN QDs structures and applicable for the fabrication of GaN-based light emitting devices.
Growth of optical-quality, uniform In-rich InGaN films using two-heater metal-organic chemical vapor deposition
(2013-11-15)
Fu, S. F.
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Chen, C. Y.
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Li, F. W.
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Hsu, C. H.
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Chou, W. C.
Good-optical-quality, thick InxGa1-xN films with high In content were grown using a homemade two-heater metal-organic chemical vapor deposition system. By varying the growth temperature, it was Found that the In composition of the InGaN epilayer varied from 18 to 59% as the substrate temperature decreased from 750 to 625 degrees C. Our results show that the optical properties in terms of the emission peak wavelength and linewidth are uniformly distributed throughout the entire 2 in. wafer for the x=0.40 InGaN sample. The resultant mean peak wavelength and FWHM are 808 +/- 6 nm and 229 +/- 18 meV, respectively, at 18 K. In addition, for the InGaN film grown at 625 degrees C, a noticeable decrease in the In composition occurred when the ceiling temperature was >800 degrees C, indicative of the occurrence of parasitic reactions in the gas phase. (C) 2013 Elsevier B.V. All rights reserved.
Impacts of ammonia background flows on structural and photoluminescence properties of InN dots grown on GaN by flow-rate modulation epitaxy
(2006-12-25)
Ke, W. C.
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Lee, L.
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Chen, C. Y.
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Tsai, W. C.
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Chang, W. -H.
Structural and photoluminescence (PL) properties of InN dots grown on GaN by metal organic vapor phase epitaxy using the flow-rate modulation technique, and their dependence on growth conditions, were investigated. An ammonia (NH3) background flow was intentionally supplied during indium deposition periods to control the kinetics of adatoms and hence the morphology of InN dots. Samples prepared under lower NH3 background flows generally exhibit narrower and more intense PL signals peaked at lower emission energies. The authors point out that the NH3 background flow is an important parameter that controls not only the nucleation process but also the emission property of InN dots. (c) 2006 American Institute of Physics.
MIXING EFFICIENCY VIA ALTERNATING INJECTION IN A HETEROGENEOUS POROUS MEDIUM
(2018-04-01)
Li, J. S.
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Li, Q.
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Cai, W. H.
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Li, F. C.
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Chen, C. Y.
We numerically verify better fluid mixing efficiency can be achieved by alternating injection scheme in a heterogeneous porous medium, whose permeability heterogeneity is characterized by two statistical parameters, i.e., the variance s and the correlation length 1. Nevertheless, the fingering pattern is strongly affected by permeability distribution to result in similar fingering interface on each of injected layer of less viscous fluids. Instead of randomly chaotic fingering interaction in a homogeneous condition, more orderly channeling interaction occurs in a heterogeneous medium. As a result, higher Peclet number Pe (relative measure of advection and diffusion effects) generally leads to worse mixing efficiency in a heterogeneous medium, which might contradict the result found in a homogeneous case. By the same token, in the cases which strong chaotic fingering interaction already exists in homogeneous conditions, e.g., sufficiently short alternating injection interval Delta t, large viscosity contrast A and high Pe, the presence of permeability heterogeneity would constrain the randomly chaotic fingering interaction and favors the more orderly channeling interaction, so that mixing efficiency is deteriorated compared with the corresponding homogeneous case.
Optical characterization of isoelectronic ZnSe(1-x)O(x) semiconductors
(2011-05-15)
Lin, Y. C.
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Chung, H. L.
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Ku, J. T.
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Chen, C. Y.
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Chien, K. F.
We have studied the temperature dependence of the band gap and the decay dynamics of isoelectronic ZnSe(1-x)O(x) (x=0-0.053) semiconductors, using photoluminescence (PL) and time-resolved PL spectroscopy. The temperature dependence of the band gap of ZnSe(1-x)O(x) decreases with the increase in 0 concentration. The Kohlrausch law is in good agreement with the O-induced complex decay profiles. As temperature increases, the mechanism of carrier decay undergoes a complicated change from trapped to free excitons. These findings are consistent with the temperature dependence of the stretching exponent beta. (C) 2010 Elsevier B.V. All rights reserved.
Optical characterization of isoelectronic ZnSe1-xOx semiconductors
(2011-05-15)
Lin, Y. C.
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Chung, H. L.
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Ku, J. T.
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Chen, C. Y.
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Chien, K. F.
We have studied the temperature dependence of the band gap and the decay dynamics of isoelectronic ZnSe1-xOx (x=0-0.053) semiconductors, using photoluminescence (PL) and time-resolved PL spectroscopy. The temperature dependence of the band gap of ZnSe1-xOx decreases with the increase in 0 concentration. The Kohlrausch law is in good agreement with the O-induced complex decay profiles. As temperature increases, the mechanism of carrier decay undergoes a complicated change from trapped to free excitons. These findings are consistent with the temperature dependence of the stretching exponent beta. (C) 2010 Elsevier B.V. All rights reserved.
Photovoltaic effect on the conductive atomic force microscopic characterization of thin dielectric films
(2006-09-25)
Chang, M. N.
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Chen, C. Y.
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Yang, M. J.
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Chien, C. H.
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電子工程學系及電子研究所
The authors have used front-wing conductive probes to investigate the photovoltaic effect on the conductive atomic force microscopic (C-AFM) characterization of thin dielectric films. The surface photovoltage induced by the laser beam of an atomic force microscope can enhance the electrical field across the studied dielectric film, decreasing the onset voltage of the leakage current, resulting in a modified C-AFM image with a larger current distribution. Moreover, the experimental results also revealed that the influence of the photovoltaic effect on C-AFM would be more significant for dielectric films that are grown on a substrate with a higher carrier concentration. (c) 2006 American Institute of Physics.
Pressure effect and electron diffraction on the anomalous transition in ternary superconductor Bi2Rh3Se2
(2014-01-01)
Chen, C. Y.
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Chan, C. L.
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Mukherjee, S.
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Chou, C. C.
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Tseng, C. M.
The effect of external hydrostatic pressure up to 22.23 kbar on the temperature-dependent transport properties of the ternary compound Bi2Rh3Se2 is investigated. Interestingly, the resistive anomaly at T-s similar to 250 K, previously proposed as a charge-density-wave (CDW) transition, is shifted to higher temperature with increasing pressure, in distinct contrast to an established knowledge for CDW. Using temperature-dependent electron-diffraction characterizations, we have unraveled that this transition is, in effect, of a structural phase-transformation nature, experiencing the symmetry reduction from a high-symmetry C-centered monoclinic lattice to a low-symmetry primitive one below T. A more elaborately determined room-temperature C-centered lattice was also proposed. (C) 2013 Elsevier Ltd. All rights reserved.
The Effect of Tensile Strain on Optical Anisotropy and Exciton of m-Plane ZnO
(2015-04-01)
Wang, H. H.
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Tian, J. S.
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Chen, C. Y.
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Huang, H. H.
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Yeh, Y. C.
The near band edge emission of the tensile-strained m-plane ZnO film grown on (112)LaAlO3 substrates shows abnormal low polarization degree (rho = 0.1). The temperature dependency of polarization degree clarifies the origins of different emission peaks. In tensile-strained m-plane ZnO, the [0001] polarized state is upper shifted and is overlapping with the [11 (2) over bar0] polarized state. This phenomenon causes the abnormal low polarization degree and reveals the effect of strain on the emission anisotropy of m-plane ZnO.
The joint usage of conventional medicine and alternative medicine for migraine in Taiwan: a ten-year retrospective study
(2009-10-01)
Chang, S. C.
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Hou, M. C.
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Hu, N. Z.
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Lo, L. C.
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Chen, Y. L.
The Rectenna Design on Contact Lens for Wireless Powering of the Active Intraocular Pressure Monitoring System
(2013)
Cheng, H. W.
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Jeng, B. M.
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Chen, C. Y.
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Huang, H. Y.
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Chiou, J. C.
This paper proposed a wireless power harvesting system with micro-electro-mechanical-systems (MEMS) fabrication for noninvasive intraocular pressure (IOP) measurement on soft contact lens substructure. The power harvesting IC consists of a loop antenna, an impedance matching network and a rectifier. The proposed IC has been designed and fabricated by CMOS 0.18um process that operates at the ISM band of 5.8 GHz. The antenna and the power harvesting IC would be bonded together by using flip chip bonding technologies without extra wire interference. The circuit utilized an impedance transformation circuit to boost the input RF signal that improves the circuit performance. The proposed design achieves an RF-to-DC conversion efficiency of 35% at 5.8 GHz.
The structural and optical properties of InN nanodots grown with various V/III ratios by metal-organic chemical vapor deposition
(2009-07-22)
Fu, S. F.
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Wang, S. M.
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Lee, L.
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Chen, C. Y.
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Tsai, W. C.
Self-assembled InN nanodots have been prepared at 650 degrees C with various V/III ratios from 500 to 30 000 by metal-organic chemical vapor deposition (MOCVD). It is found that the dot density and morphological size as well as the optical properties all display drastic changes at V/III = 12000. Generally, denser and smaller InN nanodots with higher emission energy and narrower linewidth were obtained when growth was conducted at V/III ratios slightly lower than 12 000 as compared to those at higher V/III ratios. The physical properties of our MOCVD-grown InN nanodots are sensitive to the surface structure and the morphology is very similar to molecular beam epitaxially grown GaN and InN films, which may be used as a guide to optimize the InN growth.
Toxicity assessment of polycyclic aromatic hydrocarbons using an air-tight algal toxicity test
(2006)
Chen, C. Y.
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Yan, Y. K.
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Yang, C. F.
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環境工程研究所
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Institute of Environmental Engineering
The existing toxicity data on the effects of polycyclic aromatic hydrocarbons (PAHs) on Pseudokirchneriella subcapitata (green alga) are quite insufficient. These data were derived using different test techniques (e.g. conventional batch test, closed-system test, semi-static test). The relative toxicity relationship for various PAHs is thus difficult to interpret. Consequently, the current toxicity database is insufficient and also inadequate for analyses of the effects of PAHs on P. subcapitata. This study evaluated the toxicity city of eleven PAHs using an air-tight test technique. The relative toxicity relationship was determined on a uniform basis, and was different from the relationship based on current available data. P. subcapitata. was found to be more susceptible to PAHs than Daphnia magna, fathead minnow, and Scenedesmus subspicatus. Quantitative structure-activity relationship (QSAR) was established based on the chemical's hydrophobicity with R-2 equal to 0.88. Photo-induced toxicity for various PAHs was also explored by exposing PAHs under UV-photoactivation. Toxicity of anthracene, benzanthrone, and benz[a]anthracene was found to increase 3.5 to 25 times after UV exposure. Phototoxicity was observed when the HOMO-LUMO gap varied between 6.8 and 8.0 eV.
Very small photoluminescent gold nanoparticles for multimodality biomedical imaging
(2013-05-01)
Lai, Sheng-Feng
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Chien, Chia-Chi
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Chen, Wen-Chang
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Chen, Hsiang-Hsin
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Chen, Yi-Yun
An original synthesis method based on X-ray irradiation produced gold nanoparticles (AuNPs) with two important properties for biomedical research: intense visible photoluminescence and very high accumulation in cancer cells. The nanoparticles, coated with MUA (11-mercaptoundecanoid acid), are very small (1.4 nm diameter); the above two properties are not present for even slightly larger sizes. The small MUA-AuNPs are non-cytotoxic (except for very high concentrations) and do not interfere with cancer cell proliferation. Multimodality imaging using visible light fluorescence and X-ray microscopy is demonstrated by tracing the nanoparticle-loaded tumor cells. (C) 2012 Elsevier Inc. All rights reserved.
Visual Fatigue Difference Analysis between Reflective and Emissive Backlight of Electronic-Book Readers
(2011)
Wen, B. J.
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Lai, Y. Y.
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Tsai, T. C.
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Ke, M. T.
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Chen, C. Y.
The purpose of this study is to analyze the visual fatigue difference between electronic-book readers based on reflective and emissive backlight. Kindle DXs and iPads are used as the electronic-book readers. In addition, this study also analyzes the visual fatigue difference between paper readers and electronic-book readers. As a result, the experimental result based on A4 paper is used for reference data. According to the visual fatigue difference analysis, it is suggested that electronic-book reader based on reflective backlight is not cause more significant visual fatigue with reading than one based on emissive backlight. Therefore, paper books will be replaced by electronic-book reader based on reflective backlight in the near future, because its reusable feature obviously reduces office or home paper consumption, and of course, protects natural resources from being wasted, a goal that human being is striving to reach.