Browsing by Author "Chang, Y. C."

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ab initio calculated frequency-dependent nonlinear optical properties on CsGeBr3
(2006-01-01)
Tang, L. C.
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Chang, Y. C.
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Huang, J. Y.
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Chang, C. S.
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光電工程學系
A systematic first-principles calculation of the linear and second-order optical susceptibilities as functions of frequency for CsGeBr3 is presented. Specifically, we study the relation between the structural properties and the optical responses. Three structural deformation factors, Delta alpha, d(Ge), d(X) are used to express the degree of distortion from the ideal perovskite structure in bond angle, Ge position, and anion position, respectively. Based on our first-Principles studies, we find that Delta alpha and d(Ge) increase, while d(X) decreases as we substitute the halo-en ion from Cl to Br and then to I. The dielectric function and the second harmonic generation coefficient are also found to increase with increasing Delta alpha and d(Ge). Our calculation indicates that the direct bandgap, E-g, of CsGeX3 occurs at the R-point for all three compounds, and its magnitude decreases as Delta alpha and d(Ge) increase (i.e. E-g(CsGeI3) < E-g(CsGeBr3) < E-g(CsGeCl3)). Our partial density of states (PDOS) analysis reveals that the valence band maximun (VBM) and conduction band minimum (CBM) are mainly associated with the p-orbitals of Germanium. Interband and intraband analysed results for chi((2))(ijk) in CsGeBr3 can be separated into two main groups of peaks. One was contributed from the magnitude electronic bandgap; the other part was recognized to be attribution from the distortional structural factors. The magnitudes Of chi((2))(ijk) were in the same manner with some reported experiment near the band gap.
An analytical solution for tidal fluctuations in unconfined aquifers with a vertical beach
(2010-10-22)
Yeh, H. D.
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Huang, C. S.
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Chang, Y. C.
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Jeng, D. S.
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環境工程研究所
The perturbation technique has been commonly used to develop analytical solutions for simulating the dynamic response of tidal fluctuations in unconfined aquifers. However, the solutions obtained from the perturbation method might result in poor accuracy for the case of the perturbation parameter being not small enough. In this paper, we develop a new analytical model for describing the water table fluctuations in unconfined aquifers, based on Laplace and Fourier transforms. In the new approach, the mean sea level is used as the initial condition and a free surface equation, neglecting the second-order slope terms, as the upper boundary condition. Numerical results show that the present solution agrees well with the finite different model with the second-order surface terms. Unlike Teo et al.'s (2003) approximation which restricts on the case of shallow aquifers, the present model can be applied to most of the tidal aquifers except for the very shallow one. In addition, a large-time solution in terms of sine function is provided and examined graphically with four different tidal periods.
An energy adjustable linearly polarized passively Q-switched bulk laser with a wedged diffusion-bonded Nd:YAG/Cr4+:YAG crystal
(2015-03-23)
Cho, C. Y.
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Cheng, H. P.
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Chang, Y. C.
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Tang, C. Y.
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Chen, Y. F.
An energy adjustable passively Q-switched laser is demonstrated with a composite Nd:YAG/Cr4+:YAG crystal by applying a wedged interface inside the crystal. The theoretical model of the monolithic laser resonator is explored to show the energy adjustable feature with different initial transmissions of the saturable absorber at the horizontal axis. By adjusting the pump beam location across the Nd: YAG crystal, the output pulse energy can be flexibly changed from 10.9 mu J to 17.6 mu J while maintaining the same output efficiency. The polarization state of the laser output is found to be along with the polarization of the C-mount pump diode. Finally, the behavior of the multi-transverse-mode oscillation is also discussed for eliminating the instability of the pulse train. (C) 2015 Optical Society of America
Broad Angular and Spectral Anti-Reflection Employing GaN Nano-Pillar Structures
(2008)
Chiu, C. H.
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Yu, Peichen
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Chen, C. C.
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Kuo, H. C.
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Lu, T. C.
Angular and spectral reflectivities of GaN nano-pillar structures are investigated for heights of 350nm, 550nm and 720 nm. Calculations based on rigorous coupled-wave analysis show excellent agreement with the measured reflectivities for s- and p-polarizations. (c) 2008 Optical Society of America
Broadband and omnidirectional antireflection employing disordered GaN nanopillars
(2008-06-09)
Chiu, C. H.
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Yu, Peichen
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Kuo, H. C.
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Chen, C. C.
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Lu, T. C.
Disordered GaN nanopillars of three different heights: 300, 550, and 720 nm are fabricated, and demonstrate broad angular and spectral anti-reflective characteristics, up to an incident angle of 60 degrees and for the wavelength range lambda=300-1800nm. An algorithm based on a rigorous coupled-wave analysis (RCWA) method is developed to investigate the correlations between the reflective characteristics and the structural properties of the nanopillars. The broadband and omnidirectional antireflection arises mainly from the refractive-index gradient provided by nanopillars. Calculations show excellent agreement with the measured reflectivities for both s- and p-polarizations. (c) 2008 Optical Society of America.
Compensation effect and differential capacitance analysis of electronic energy band structure in relaxed InAs quantum dots
(2010-09-15)
Chen, J. F.
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Chen, Ross C. C.
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Chiang, C. H.
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Hsieh, M. C.
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Chang, Y. C.
The use of a differential capacitance technique for analyzing the effect of strain relaxation on the electronic energy band structure in relaxed InAs self-assembled quantum dots (QDs) is presented. Strain relaxation is shown to induce a deep defect state and compensate the ionized impurity in the bottom GaAs layer, leading to a double depletion width and a long emission time. An expression of capacitance at different frequency and voltage is derived for analyzing the experimental data. It has been shown that the relationship between the low-frequency and high-frequency capacitances can be well explained by a Schottky depletion model with a compensated concentration in the bottom GaAs layer. A simple expression is presented to account for the modulation of the free electrons in the top GaAs layer. This capacitance analysis shows a long low-energy tail for the electron ground state, suggesting not very uniform strain relaxation. The results of this study illustrate a carrier compensation effect of the defect state on the electronic energy band structure near the QDs. (C) 2010 American Institute of Physics. [doi:10.1063/1.3467938]
Defect density reduction of the Al(2)O(3)/GaAs(001) interface by using H(2)S molecular beam passivation
(2011-10-01)
Merckling, C.
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Chang, Y. C.
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Lu, C. Y.
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Penaud, J.
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Brammertz, G.
The integration of higher carrier mobility materials to increase drive current capability in the next CMOS generations is required for device scaling. But a fundamental issue regarding the introduction of high-mobility III-V in CMOS is the electrical passivation of the interface with the high-kappa gate dielectric. In this work, we show that in situ H(2)S surface treatment on GaAs(001) leads to a stable and reorganized oxide/III-V interface. The exposition of the GaAs surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. Finally, MOS capacitors are fabricated to extract interface state density over the band gap. These results highlight a promising re-interest in chalcogenide passivation of III-V surfaces for CMOS applications. (C) 2011 Elsevier B.V. All rights reserved.
Defect density reduction of the Al2O3/GaAs(001) interface by using H2S molecular beam passivation
(2011-10-01)
Merckling, C.
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Chang, Y. C.
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Lu, C. Y.
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Penaud, J.
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Brammertz, G.
The integration of higher carrier mobility materials to increase drive current capability in the next CMOS generations is required for device scaling. But a fundamental issue regarding the introduction of high-mobility III-V in CMOS is the electrical passivation of the interface with the high-kappa gate dielectric. In this work, we show that in situ H2S surface treatment on GaAs(001) leads to a stable and reorganized oxide/III-V interface. The exposition of the GaAs surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. Finally, MOS capacitors are fabricated to extract interface state density over the band gap. These results highlight a promising re-interest in chalcogenide passivation of III-V surfaces for CMOS applications. (C) 2011 Elsevier B.V. All rights reserved.
Development of optimised carrier sequence in MCU-based random-frequency PWM
(2007-01-01)
Chen, H. C.
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Chang, Y. C.
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Huang, C. K.
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電控工程研究所
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Institute of Electrical and Control Engineering
The effect of the carrier sequences on the voltage spectrum of MCU(microcontroller)based random-frequency pulse-width modulation (RFPWM) is presented. To optimise the carrier sequence efficiently, first all possible sequences are classified into groups according to the time-shift and time-reverse properties of the Fourier transform. Then, some evaluation indexes are proposed to obtain the optimal sequence quickly with the end of a personal computer (PC). Finally, some optimised carrier sequences with only two carrier frequencies are recommended. The experimental results also indicate that we should pay more attentions to the carrier sequences than to the selection of carrier frequency and on the numbers of carrier frequencies.
Electrochemical Degradation of Nafion Ionomer to Functionalize Graphene As a Support for Core-Shell Palladium-Ruthenium Alloy @ Platinum Electrocatalysts
(2016-01-01)
Kuo, C. C.
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Chang, Y. C.
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Chou, C. L.
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Chou, S. C.
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Wu, P. W.
A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps are performed in H2SO4 aqueous solution on electrodes containing carbon cloth, graphene, and Nafion ionomer. With supply of ambient oxygen, the formation of hydroxyl radicals from the oxygen reduction reaction during CV cycles initiates the decomposition of Nafion ionomer that engenders oxygenated functional groups on the graphene surface. Raman analysis suggests a minor change for the graphene structure. Exploring various amounts of Nafion ionomer, we determine the optimized conditions for graphene functionalization. Contact angle is used to evaluate the effect of Nafion ionomer decomposition. X-ray photoelectron spectroscopy is employed to study relevant functional groups. Afterwards, nanoparticles of Pd9Ru are synthesized and impregnated on those functionalized graphene (FGN) via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples suggest successful formation of alloy. Images from transmission electron microscope confirm the average size of 3-4 nm. As expected, the Pd9Ru alloy are much more dispersive in FGN rather than in the one without functionalization.
Equalization and Pre-distorted Schemes for Increasing Data Rate in In-door Visible Light Communication System
(2011)
Liu, Y. F.
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Chang, Y. C.
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Chow, C. W.
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Yeh, C. H.
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光電工程學系
We propose and demonstrate using signal pre-distortion and equalization schemes for increasing the data rate of the white-light LED communication system. Bit-error-rate of <10(-10) at 10-Mb/s operation was achieve using 1-MHz bandwidth white-light LED. (C) 2011 Optical Society of America
Examining the effects of learning motivation and of course design in an instructional simulation game
(2010)
Chang, Y. C.
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Peng, H. Y.
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Chao, H. C.
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教育研究所
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工業工程與管理學系
In recent years, games have been proven to be an effective tool in supplementing traditional teaching methods. Through game playing, students can strengthen their cognitive-recognition architecture and can gain satisfaction as well as a sense of achievement. This study presents a conceptual framework for examining various effective strategies by which instructors can both integrate games into courses and strengthen games' positive influence on students' learning motivations. We used a flexible web-based instructional game called the Simulation of Production and Logistics Environment (SIMPLE) game in three decision-science courses in industrial engineering. Through this use, we evaluated the perceptions and the learning motivation attributable to a group of students after they played the SIMPLE game. We also explored the relationships between the course design and the students' learning motivations. We collected data from 139 students in the three courses and analysed the materials by using descriptive statistics, an independent t-test, a multiple regression analysis, one-way analysis of variance and Pearson correlation. Results showed that instructors' teaching strategies enhanced students' motivation to play the SIMPLE game and that students' learning motivation affected the students' acceptance of the SIMPLE game. The results also showed a clear and strong relationship between students' background and students' acceptance of the SIMPLE game in these three courses. By combining appropriate approaches to adopting the SIMPLE game and appropriate approaches to teaching students about production and logistics decision-making situations, instructors can create an effective learning environment for peer interaction, for learning motivation and for course-directed learning interest.
H(2)S molecular beam passivation of Ge(001)
(2011-04-01)
Merckling, C.
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Chang, Y. C.
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Lu, C. Y.
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Penaud, J.
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El-Kazzi, M.
A fundamental issue regarding the introduction of high-mobility Ge channels in CMOS circuits is the electrical passivation of the interface with the high-k gate dielectric. In this paper, we investigate the passivation of p-Ge(0 0 1) using molecular H(2)S. The modification of the semiconductor surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. MOS capacitors are fabricated to extract interface state density, and finally we demonstrate the efficiency of the passivation scheme using a combination with an ultra thin Al interlayer. (C) 2010 Elsevier B.V. All rights reserved.
H2S molecular beam passivation of Ge(001)
(2011-04-01)
Merckling, C.
;
Chang, Y. C.
;
Lu, C. Y.
;
Penaud, J.
;
El-Kazzi, M.
A fundamental issue regarding the introduction of high-mobility Ge channels in CMOS circuits is the electrical passivation of the interface with the high-k gate dielectric. In this paper, we investigate the passivation of p-Ge(0 0 1) using molecular H2S. The modification of the semiconductor surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. MOS capacitors are fabricated to extract interface state density, and finally we demonstrate the efficiency of the passivation scheme using a combination with an ultra thin Al interlayer. (C) 2010 Elsevier B.V. All rights reserved.
Improvement on the estimation of constant-rate drawdown in large-diameter wells
(2013-04-01)
Chang, Y. C.
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Yeh, H. D.
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Wang, C. T.
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環境工程研究所
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Institute of Environmental Engineering
Papadopulos and Cooper's (PC) solution can be used to describe the drawdown resulting from pumping with a constant rate at a large-diameter well. However, this solution is too complicated to be accurately evaluated due to the oscillatory nature of the Bessel functions. The PC approach resulted in tabulated values of dimensionless drawdown at the well with an accuracy of four or fewer digits for selected values of dimensionless storage coefficient versus dimensionless time. Some researchers have fitted the tabulated values with interpolation formulas that are easy to use in engineering applications. Those formulas may be more accurate if the tabulated values are computed with greater accuracy. In this study, we propose an efficient numerical procedure, including a root search scheme, to find the roots of the integrand, Gaussian quadrature for numerical integration, and Shanks transform to accelerate convergence of infinite series. The proposed procedure can evaluate the dimensionless drawdown with greater accuracy and is useful in practice if there is a need for high accuracy for the observation either at the well or in the aquifer at some distance from the pumping well Editor D. Koutsoyiannis Citation Chang, Y.C., Yeh, H.D., and Wang, C.T., 2013. Improvement on the estimation of constant-rate drawdown in large-diameter wells. Hydrological Sciences Journal, 58 (3), 716727.
Investigation of the electronic, linear and second-order nonlinear optical properties for the wide bandgap chalcopyrite ternary nitrides
(2008)
Tang, L. C.
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Chang, Y. C.
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Huang, J. Y.
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Chang, C. S.
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光電工程學系
We present the results of the ab initio calculated electronic properties, first and second harmonic generation for the A(II)B(IV) N(2), (A(II)=Be, B(IV)=C, Si, Ge) compounds with chalcopyrite structure performed using the Linear Augmented Slater-Type Orbitals (LASTO) method. The second-order optical susceptibilities as functions of frequency for A(II)B(IV)N(2) are also presented. Specifically, we study the relation between the structural properties and the optical responses. Our electronic band structure and density of states (PDOS) analysis reveal that the underestirnate bandgaps of these chalcopyrite A(II)B(IV)N(2) are wide enough (from 4eV to 6eV), direct transition and mainly located at F-point. Calcultion results show this new category wide-bandgap ternary nitrides has potential applications in optoelectronics.
Long Photon Lifetime from Microdisk Cavity Laser with Type II GaSb/GaAs Quantum Dots
(2013-01-01)
Hsu, K. S.
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Chang, C. C.
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Lin, W. H.
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Shih, M. H.
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Lin, S. Y.
Microdisk lasers with active region made of type II GaSb/GaAs quantum dots on the GaAs substrate have been demonstrated. Lasing wavelengths near 1 mu m was achieved and longer photon lifetime from type II structure also observed. (C) 2013 Optical Society of America
Measuring process performance based on expected loss with asymmetric tolerances
(2006-12-01)
Pearn, W. L.
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Chang, Y. C.
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Wu, Chien-Wei
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工業工程與管理學系
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Department of Industrial Engineering and Management
By approaching capability from the point of view of process loss similar to C-pm, Johnson (1992) provided the expected relative loss Le to consider the proximity of the target value. Putting the loss in relative terms, a user needs only to specify the target and the distance from the target at which the product would have zero worth to quantify the process loss. Tsui (1997) expressed the index L-e as Le = L-ot + L-pe, which provides an uncontaminated separation between information concerning the process relative off-target loss (L-ot) and the process relative inconsistency loss (L-ot). Unfortunately, the index L-e inconsistently measures process capability in many cases, particularly for processes with asymmetric tolerances, and thus reflects process potential and performance inaccurately. In this paper, we consider a generalization, which we refer to as L-e", to deal with processes with asymmetric tolerances. The generalization is shown to be superior to the original index L-e. In the cases of symmetric tolerances, the new generalization of process loss indices L-e", L-ot" and L-pe" reduces to the original index L-e, L-ot, and L-pe, respectively. We investigate the statistical Properties of a natural estimator of L-e" L-ot" and L-pe" when the underlying process is normally distributed. We obtained the rth moment, expected value, and the variance of the natural estimator (L) over cap (e)", (L) over cap (ot)", and (L) over cap (pe)". We also analyzed the bias and the mean squared error in each case. The new generalization V measures process loss more accurately than the original index L-e.
Multiple-process performance analysis chart based on process loss indices
(2006-06-10)
Pearn, W. L.
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Chang, Y. C.
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Wu, Chien-Wei
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工業工程與管理學系
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Department of Industrial Engineering and Management
Control chart techniques have been widely used in the manufacturing industry for controlling and monitoring process performance and are practical tools for quality improvement. When dealing with variable data, one usually employs the (X) over bar chart and R chart ( or S chart) to detect the process mean and process variance change. These charts are easy to understand and effectively communicate critical process information without using words and formulae. In this paper, we develop a new multiple-process performance analysis chart (MPPAC), using the process loss index L-e to control the product quality and/or reliability for multiple manufacturing processes. Upper confidence bounds are applied to the L-e MPPAC to ensure the capability groupings are accurate, which is essential to product quality assurance. The L-e MPPAC displays the multiple-process relative inconsistency and process relative off-target degree on one single chart in order to provide simultaneous capability control for multiple processes. We demonstrate the applicability of the proposed L-e MPPAC incorporating the upper confidence bounds by presenting a case study on some liquid-crystal display module manufacturing processes, to evaluate the factory performance.
New solutions to the constant-head test performed at a partially penetrating well
(2009-05-05)
Chang, Y. C.
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Yeh, H. D.
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環境工程研究所
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Institute of Environmental Engineering
The mathematical model describing the aquifer response to a constant-head test performed at a fully penetrating well can be easily solved by the conventional integral transform technique. In addition, the Dirichlet-type condition should be chosen as the boundary condition along the rim of wellbore for such a test well. However, the boundary condition for a test well with partial penetration must be considered as a mixed-type condition. Generally, the Dirichlet condition is prescribed along the well screen and the Neumann type no-flow condition is specified over the unscreened part of the test well. The model for such a mixed boundary problem in a confined aquifer system of infinite radial extent and finite vertical extent is solved by the dual series equations and perturbation method. This approach provides analytical results for the drawdown in the partially penetrating well and the well discharge along the screen. The semi-analytical solutions are particularly useful for the practical applications from the computational point of view. (C) 2009 Elsevier B.V. All rights reserved.