Browsing by Author "Wu, CL"

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Carrier capture and relaxation of self-assembled ZnTe/ZnSe quantum dots prepared under Volmer-Weber and Stranski-Krastanow growth modes
(2005-02-01)
Lee, ME
;
Yeh, YC
;
Chung, YH
;
Wu, CL
;
Yang, CS
The carrier capture and relaxation of type II ZnTe/ZnSe quantum dots have been investigated with ultrafast time-resolved photo luminescence upconversion. The carrier capture times were 7 and 38 ps for the Volmer-Weber mode and Stranski-Krastanow mode, respectively. We found that the carrier relaxation of QDs exhibits faster decay under the Volmer-Weber growth mode than under the Stranski-Krastanow growth mode. We attribute the difference of carrier relaxation to the wetting layer formed in the Stranski-Krastanow growth mode. (C) 2004 Elsevier B.V. All rights reserved.
Determination of the optimal burn-in time and cost using an environmental stress approach: a case study in switch mode rectifier
(2002-04-01)
Wu, CL
;
Su, CT
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
Stress burn-in is an effective burn-in means of screening out the infant mortality components of a system which are conducted under an extremely stressful environment. While investigating stresses, screening burn-in by thermal stress, voltage stress, or mechanical shock stress, most related studies failed to develop an effective method to determine the optimal burn-in time and burn-in cost for a practical operation. Therefore, this study presents an effective procedure that adopts robust design techniques and the accelerated stress test to determine the optimal burn-in time and burn-in cost. A case study of the production of switch mode rectifier demonstrates the proposed procedure's effectiveness. Moreover, the results show that the proposed procedure generalizes well, and can screen out the early failure from material and manufacturing process. (C) 2002 Elsevier Science Ltd. All rights reserved.
Dynamical analysis of survival of Kosterlitz-Thouless pairs due to pinning
(1997-01-01)
Chang, D
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
;
Department of Electrophysics
We investigate the process of annihilation between vortices of opposite flux in superconducting thin films in the presence of randomly distributed pinning centers. The number and distribution of pairs of vortex-antivortex that avoid annihilation due to pinning on two pinning centers is estimated analytically and compared with numerical simulations. The situation can be realized, for example, when the system is quenched from high temperature (above or below the Kosterlitz-Thouless temperature) or when the current is reduced abruptly. Qualitatively two different cases can be distinguished. The simpler one is when the pairs are well separated. In this case, the problem under mild assumptions can be solved analytically. When the vortex pairs are not very rare, the situation is much more complicated because a great variety of processes become significant. We isolate the important ones and construct an iterative (real-space renormalization-group) scheme to describe the behavior of the interacting multivortex system. Some dynamical aspects of pinning and vortex motion are discussed.
Dynamical analysis of survival of Kosterlitz-Thouless pairs due to pinning
(1997-01-01)
Chang, D
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
;
Department of Electrophysics
We investigate the process of annihilation between vortices of opposite flux in superconducting thin films in the presence of randomly distributed pinning centers. The number and distribution of pairs of vortex-antivortex that avoid annihilation due to pinning on two pinning centers is estimated analytically and compared with numerical simulations. The situation can be realized, for example, when the system is quenched from high temperature (above or below the Kosterlitz-Thouless temperature) or when the current is reduced abruptly. Qualitatively two different cases can be distinguished. The simpler one is when the pairs are well separated. In this case, the problem under mild assumptions can be solved analytically. When the vortex pairs are not very rare, the situation is much more complicated because a great variety of processes become significant. We isolate the important ones and construct an iterative (real-space renormalization-group) scheme to describe the behavior of the interacting multivortex system. Some dynamical aspects of pinning and vortex motion are discussed.
Explicit four-fold symmetry breaking effect on the vortex lattice in D-wave superconductors
(1998-04-01)
Chang, D
;
Mou, CY
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
We use a recently developed effective Ginzberg-Landau equation to study the vortex lattice structure in d-wave superconductors. By introducing explicit four-fold symmetry breaking terms we are able to reproduce the small angle neutron scattering data on YBCO by Keimer et al. [9]. A phase diagram is also constructed and shows quite rich structures.
Growth and characterization of chemical-vapor-deposited zinc oxide nanorods
(2006-03-01)
Wu, CL
;
Chang, L
;
Chen, HG
;
Lin, CW
;
Chang, TF
ZnO nanorods were grown on Si substrates by metal-organic chemical vapor deposition (CVD). The ZnO nanorods were characterized by scanning electron microscopy, transmission electron microscopy (TEM), and X-ray diffraction. It was found that highly oriented ZnO single-crystalline nanorods were formed only on the substrate coated with a gold film. Without the gold, ZnO was deposited as a continuous film. No Au was observed on top of the ZnO nanorods, implying that the Au plays no role as catalytic metal in vapor-liquid-solid mechanism for formation of ZnO nanorods. In CVD, oriented ZnO nanorods along the c-axis were grown as a result of < 111 > textured Au. High-resolution TEM shows that the gold layer and ZnO are in orientation relationship of Au 111 planes//ZnO (0002) basal planes. (c) 2005 Elsevier B.V. All rights reserved.
Nanomachining of (110)-oriented silicon by scanning probe lithography and anisotropic wet etching
(1999-10-18)
Chien, FSS
;
Wu, CL
;
Chou, YC
;
Chen, TT
;
Gwo, S
We have demonstrated that silicon nanostructures with high aspect ratios, having similar to 400 nm structural height and similar to 55 nm lateral dimension, may be fabricated by scanning probe lithography and aqueous KOH orientation-dependent etching on the H-passivated (110) Si wafer. The high spatial resolution of fabricated features is achieved by using the atomic force microscope based nano-oxidation process in ambient. Due to the large (110)/(111) anisotropic ratio of etch rate and the large Si/SiO2 etch selectivity at a relatively low etching temperature and an optimal KOH concentration, high-aspect-ratio gratings with (111)-oriented structural sidewalls as well as hexagonal etch pit structures determined by the terminal etch geometry can be obtained. (C) 1999 American Institute of Physics. [S0003-6951(99)03242-8].
New findings of the electromagnetic response in superconductors
(1998-04-01)
Mou, CY
;
Chang, D
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
Based on the Ginzburg-Landau theory, two theoretical findings in the electromagnetic response of superconductors are described. First, we derive the most general linear response theory and then apply it to the charged super fluid regime, where the magnetic fluctuation is relevant. In particular, we show that a novel effect arises, in which the divergence of the conductivity tensor is suppressed by the diamagnetic susceptibilities. Secondly, we show that because of the approximated fourfold symmetry of the crystal lattice in high T-c cuprates, a non-vanishing Hall current can arise near Hc(2). This Hall current is non-linear and can become large to be observed if the applied electric field is large enough.
Static and dynamical anisotropy effects in the mixed state of d-wave superconductors
(1998-04-01)
Chang, D
;
Mou, CY
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
We describe the effects of anisotropy caused by the crystal lattice in d-wave superconductors using an effective foe-energy approach in which only one order parameter, the d-wave order-parameter field, is used. The Abrikosov parameter beta(A) is calculated analytically for both static and moving vortex lattices. The analytic expression provides an unambiguous determination of the vortex-lattice structure. We also calculate both direct and Hall I-V curves as functions of the angle between the current and the crystal-lattice orientation. In particular, we show that near H-c2 the fourfold symmetry of the crystal lattice causes asymmetric motions of particles and holes, resulting in a nonvanishing Hall current.
The effect of anisotropy on vortex lattice structure and flux flow in d-wave superconductors
(1998-04-01)
Chang, D
;
Mou, CY
;
Rosenstein, B
;
Wu, CL
;
電子物理學系
We describe effects of anisotropy caused by the crystal lattice in d-wave superconductors using effective free energy approach in which only one order parameter, the d-wave order parameter field, is used. The Abrikosov parameter beta(A) is calculated analytically for both static and moving vortex lattices. The analytic expression provides an unambiguous determination of the vortex lattice structure. We also calculate both direct and Hall I-V curves as functions of the angle between the current and the crystal lattice orientation. In particular, we show that near H-c2 the fourfold symmetry of the crystal lattice causes asymmetric motions of particles and holes, resulting in a non-vanishing Hall current.