Browsing by Author "Hsu, SY"

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A method of measuring the contribution of the image potential energy of the shallow impurity ground state in a quantum well
(2001-10-01)
Yang, TJ
;
Hsu, SY
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電子物理學系
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Department of Electrophysics
We show that the binding energy of the shallow impurity (at the center of the quantum well) ground state is strongly reduced by the presence of a metallic mirror at a few effective Bohr radii from the quantum well. For a given depth of the quantum well, we find that the absolute value of the image potential energy without the metallic mirror is equal to that with a fixed metallic mirror while a certain width of the quantum well is met. Hence. it is proposed that the binding energy of the shallow impurity ground state in the quantum well with and without the metallic mirror can be separately measured by the variation of the width of quantum well. The contribution of the image potential energy to the binding energy of the shallow impurity ground state may then be deduced. (C) 2001 Elsevier Science B.V. All rights reserved.
A new data-aided OFDM symbol timing synchronization algorithm based on histogram processing
(2005)
Sang, TH
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Hsu, SY
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Chen, TL
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A new data-aided OFDM symbol timing synchronization method is developed with two goals in mind: to achieve robust performance and to reduce computational cost. It is the intuitive observation of the relationship between the symbol timing shift and the constellation rotation on each subcarrier of an OFDM symbol from which the new method is developed. A histogram-based algorithm is used to extract the timing shift information from the FFT output. Simulations are conducted to verb the effectiveness and robustness of this new algorithm. Comparison with commonly-used algorithms based on correlation is also provided.
Anisotropy transition of Co in IrMn/Co/FeOx/Co by field cooling
(2006-04-15)
Shen, CT
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Lai, CH
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Huang, PH
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Hsu, SY
;
Chung, TY
The temperature dependence of Co anisotropy on a nano-FeOx layer was studied in the structure of IrMn/Co (FM1)/FeOx/Co (FM2). An anisotropy transition of the FM2 was observed from a combination of uniaxial and unidirectional anisotropies at room temperature (RT) to unidirectional anisotropy at temperature below 80 K through field cooling process. Various ferromagnetic (FM) and antiferromagnetic (AFM) components existing in the FeOx layer were attributable to the observed anisotropy of FM2. AFM domains with T-N higher than room temperature were responsible for the observed uniaxial anisotropy at RT and AFM domains with T-N of 80 K were accountable for the anisotropy transition, below which the unidirectional anisotropy became dominant. In addition, the direction of the shifted loop could be determined by the cooling field direction. (C) 2006 American Institute of Physics.
Coulomb tunneling anomaly in disordered copper-germanium alloys
(2000-04-01)
Hsu, SY
;
Wang, IC
;
Liao, JT
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電子物理學系
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Department of Electrophysics
We have performed electronic tunneling density of states and resistivity measurements in three-dimensional CuxGe100-x films spanning the weakly and strongly localized regimes. We found that the Coulomb anomaly in tunneling density of states in the strongly disordered regime is very profound and grows in strength with resistivity. However, when the system becomes less disorderly and approaches the weakly disordered regime, this anomaly weakens rapidly. The data suggest that the disorder enhanced electron-electron interaction effects can drive the crossover from weak: disorder to strong disorder in CuGe alloy system. (C) 2000 Elsevier Science B.V. All rights reserved.
Detection of the domain structure change using magnetotransport for a series of circular Permalloy dots
(2006-04-15)
Chung, TY
;
Hsu, SY
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電子物理學系
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Department of Electrophysics
The magnetic structure of a magnetic dot depends on its geometrical factors such as thickness and dot size and can be either a multidomain state or a vortex state. The magnetoresistance (MR) of a series of magnetic dots with diameters ranging from 0.3 to 5 mu m was measured to investigate the correlation between domain-structure and magnetotransport properties. A dot with a diameter of less than 2 mu m has a domain of vortex state at remanence and demonstrates similar reversible MR results. Moreover, the behaviors of MR show clear changes corresponding to the domain-structure change from vortex to multidomain states with an increasing dot diameter. Data can be qualitatively described by the anisotropic magnetoresistive effect. Hence, our results show that the magnetotransport can be a tool to detect the magnetic domain structure of a submicron magnetic dot. (C) 2006 American Institute of Physics.
Due date assignment using artificial neural networks under different shop floor control strategies
(2004-05-01)
Hsu, SY
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Sha, DY
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工業工程與管理學系
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Department of Industrial Engineering and Management
Due date assignment (DDA) is the first important task in shop floor control. Due date-related performance is impacted by the quality of the DDA rules. Assigning order due dates and delivering the goods to the customer on time will enhance customer service and provide a competitive advantage. A new methodology for lead-time prediction, artificial neural network (ANN), is adopted to model new due date assignment rules. An ANN-based DDA rule, combined with simulation technology and statistical analysis, is presented. Whether or not the ANN-based DDA rule can outperform the conventional and Reg-based DDA rules taken from the literature is examined. The interactions between the DDA, order review/release (ORR), and dispatching rules significantly impact upon one another, and it is therefore very important to determine a suitable DDA rule for the various combinations of ORR and dispatching rules. From the simulation and statistical results, the ANN-based DDA rules perform better in due date prediction. The ANN-based DDA rules have a smaller tardiness rate than the other rules. ANN-based DDA rules have a better sensitivity and variance. Therefore, if system information is not difficult to obtain, the ANN-based DDA rule can perform a better due date prediction. This paper provides suggestions for DDA rules under various combinations of ORR and dispatching rules. ANN-Sep is suitable for most of these combinations, especially when ORR, workload regulation (WR) and two boundaries (TB), rules are adopted.
Due-date assignment in wafer fabrication using artificial neural networks
(2004-05-01)
Sha, DY
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Hsu, SY
;
工業工程與管理學系
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Department of Industrial Engineering and Management
Due-date assignment (DDA) is the first important task of shop floor control in wafer fabrication. Due-date related performance is impacted by the quality of the DDA rules. Assigning order due dates and timely delivering the goods to the customer will enhance customer service and competitive advantage. A new methodology for lead-time prediction, artificial neural network (ANN) prediction is considered in this work. An ANN-based DDA rule combined with simulation technology and statistical analysis is developed. Besides, regression-based DDA rules for wafer fabrication are modelled as benchmarking. Whether neural networks can outperform conventional and regression-based DDA rules taken from the literature is examined. From the simulation and statistical results, ANN-based DDA rules perform a better job in due-date prediction. ANN-based DDA rules have a lower tardiness rate than the other rules. ANN-based DDA rules have better sensitivity and variance than the other rules. Therefore, if the wafer fab information is not difficult to obtain, the ANN-based DDA rule can perform better due-date prediction. The SFM_sep and JIQ in regression-based and conventional rules are better than the others.
Electron-electron interaction dominated quantum transport in thick CuGe films
(2000-07-01)
Hsu, SY
;
Shen, FJ
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Lin, JJ
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電子物理學系
;
物理研究所
We have successfully made a series of thick CuxGe100-x films spanning the weakly and strongly localized regimes. With decreasing mole concentration of Cu relative to Ge, the resistivity of film becomes bigger at a given temperature and demonstrates a stronger temperature dependence at low temperatures. When x is big, 46 less than or equal to x less than or equal to 56, resistivity increases with the square root of the decreasing temperature, implying a weak-disorder behavior. For x small, 14 less than or equal to x less than or equal to 2.0, resistivity increases exponentially with decreasing temperature, implying a strongly localized behavior. The results show that the low-temperature transport in these films is dominated by the disorder enhanced electron-electron interaction effects. (C) 2000 Elsevier Science B.V. All rights reserved.
Inelastic electron dephasing times in CuxGe100-x alloys
(2000-05-01)
Lin, JJ
;
Sheng, PJ
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Hsu, SY
;
電子物理學系
;
物理研究所
We have studied the inelastic electron dephasing scattering times, tau(i). in disordered CuxGe100-x(35 less than or equal to x less than or equal to 60) alloys between I and 15 K. The values of tau(i)(-1) (similar to T-p), and especially the exponent of temperature p, are extracted from weak localization studies. We find that the value of p continuously decreases from similar to 3 to similar to 1 as x gradually decreases from 60 to 35. Our observation is understood in terms of a crossover of the inelastic electron dephasing in impure metals from e-Fh scattering to critical e-e scattering as the disorder greatly increases and the system moves significantly toward the mobility edge. (C) 2000 Elsevier Science B.V. All. rights reserved.
Negative magnetoresistance, negative electroresistance, and metallic behavior on the insulating side of the two-dimensional superconductor-insulator transition in granular Pb films
(2006-04-01)
Barber, RP
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Hsu, SY
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Valles, JM
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Dynes, RC
;
Glover, RE
Granular Pb thin films on the insulating side of the two-dimensional superconductor-insulator transition are observed to exhibit a large negative magnetoresistance and electroresistance (change in resistance with electric field) at low temperatures. At high measurement voltages and low temperatures, the film resistances become temperature independent creating a "metallic" state. These phenomena are explained as manifestations of transport due to intergranular quasiparticle tunneling. This explanation might also provide insights into the similar behavior observed in other superconductors.
Purification of multi-walled carbon nanotubes by microwave digestion method
(2004-04-01)
Chen, CM
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Chen, M
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Leu, FC
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Hsu, SY
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Wang, SC
Here developed is an efficient method for purification of multi-walled carbon nanotubes synthesized by electron cyclotron resonance chemical vapor deposition (ECRCVD). Carbon nanotubes may find their limited use for some applications as they contain a small fraction of metal catalysts in the tubes and tend to have defects along the graphene tube wall. Defects within the multi-walled carbon nanotubes would reduce electrical and structure properties. A two-step acidic treatment in microwave digestion system is used to dissolve metal catalysts. HNO3 or HCl can rapidly absorb microwave heat and energy and completely dissolve metal, which reside in carbon nanotubes without damage. The processing time of the two-step microwave-assisted and acid-treated time to dissolve metal in the MWCNTs is below 1 h. After purification, the amount of residual catalyst metals in samples is estimated by using the thermogravimetric analysis (TGA). The results show that a high-yield of multi-walled carbon nanotubes with approximately 5% of metal is obtained. (C) 2003 Elsevier B.V. All rights reserved.
Quadratic temperature dependence of the electron-phonon scattering rate in disordered metals
(1999-08-01)
Hsu, SY
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Sheng, PJ
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Lin, JJ
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電子物理學系
;
物理研究所
We have measured the electron-phonon scattering rates 1/tau(ep) from a weak-localization study of a series of high-resistivity tin-doped Ti73Al27 alloys. The resistivities of these alloys are essentially the same and are so high that the electron elastic mean free path I approaches the interatomic spacing, resulting in a very small value of q(ph) l approximate to 0.0056 T (q(ph) is the wave number of the thermal phonons, and T is the temperature). Based on as many as about 60 magnetoresistivity measurements between 2 and 22 K, we are able to determine the dependence of 1/tau(ep) on T to within a great degree of accuracy and find that 1/tau(ep) varies essentially with T-2 in the dirty limit (q(ph) l much less than 1). This observation is not understood in terms of the current theoretical concept of electron-phonon interaction in disordered metals. [S0163-1829(99)05030-4].
Spin-orbit scattering effect on electron-electron interactions in disordered metals
(2001-09-01)
Lin, JJ
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Hsu, SY
;
Lue, JC
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Sheng, PJ
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電子物理學系
We have measured the low-temperature resistivities of a series of bulk crystalline disordered Ti73-xAl27Snx alloys (x less than or similar to 5) as well as the sheet resistances of a number of thin ferromagnetic Ni films (approximate to 120 Angstrom thick) sandwiching an ultrathin Ag or Au (less than or similar to5 Angstrom) layer. The level of impurities (concentration of Sn in the former ease, and thickness of Ag or Au in the latter case) is progressively increased in order to enhance the spin-orbit scattering in a controllable manner. The influence of the spin-orbit scattering on the electron-electron interaction effects is studied from the temperature dependence of resistivities (sheet resistance) at low temperatures. We find that the electron-electron interaction contribution to the resistivities (sheet resistances) increases slightly with increasing spin-orbit scattering. Our observation is discussed in terms of the current theoretical concept for the electron-electron interactions in disordered metals. (C) 2001 Elsevier Science Ltd. All rights reserved.
Superconducting behaviors of copper-germanium alloys
(2003-05-01)
Hsu, SY
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Chen, JY
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電子物理學系
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Department of Electrophysics
We have observed superconducting properties in three dimensional CuxGe100-x samples with 38 less than or equal to x less than or equal to 67. Transition temperature T-c is about 0.4 K. Upper critical magnetic field H-c2 has been measured in these samples confirming that they are indeed superconductors. Near the zero field T-co, H-c2 depends linearly on temperature. Our results show robust superconducting properties present in CuGe samples with weakly disorder. (C) 2003 Elsevier Science B.V. All rights reserved.
Superconducting fluctuation magnetoconductance in a tungsten carbide film
(2001-11-05)
Rosenbaum, R
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Hsu, SY
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Chen, JY
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Lin, YH
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Lin, JJ
Magnetoconductance (MC) measurements have been performed on a 2140 Angstrom thick tungsten carbide film at temperatures very close to the superconducting transition temperature T-c of the film. The data are dominated by superconducting fluctuations. A novel three-dimensional phenomenological model is proposed to explain the MC data, yielding good fits. The Larkin beta factor, beta (Larkin), appeared as a fitting parameter. An expression proposed by Larkin for beta (Larkin) failed badly for temperatures extremely close to T-c. But at intermediate and high temperatures compared to T-c, Larkin's expression gave very good agreement in fits to the MC data. At temperatures very close to T-c, a crossover from three dimensions to two dimensions was observed in the behaviour of the MC of the film.
Tunneling measurements of fluctuation effects near the superconductor to insulator transition
(1998-10-01)
Hsu, SY
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Chervenak, JA
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Valles, JM
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電子物理學系
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Department of Electrophysics
We present measurements of the temperature dependence of the tunneling density of states near the Fermi energy, G(o)(T), and resistive transitions, R(T), of ultrathin PbBi films. Both R(T) and G(o)(T) broaden substantially near the superconductor to insulator transition (SIT). The broadening in R(TI is not affected by the proximity of a ground plane suggesting that long range Coulomb interactions are not important to the SIT. The results suggest that the transport properties of Alms near the SIT are influenced by fluctuations in both the phase and the amplitude of the order parameter. We discuss the data in terms of recent theories of the superconducting transition in low superfluid density systems. (C) 1998 Elsevier Science Ltd. All rights reserved.
Unified picture of spin-dependent transport in GMR multilayered structures and bulk ferromagnetic alloys
(1998-01-01)
Schroeder, PA
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Holody, P
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Loloee, R
;
Vouille, C
;
Barthelemy, A
We have observed a positive (inverse) CPP-MR in magnetic multilayers of the forms: (a) ((X) under bar Y/Cu/Co/Cu)(n) with (X) under bar Y being the alloys <(Fe)under bar>Cr, <(Fe)under bar>V. <(Ni)under bar>Cr, <(Co)under bar>Cr, and (b) (Z/Cr/NiFe/Cr)(n) with Z = Fe and Co, For (a) the inverted results arise primarily from spin-dependent scattering in the bulk of the alloy, and are linked consistently to: (1) their magnetization: (2) band-structure calculations and (3) resistivity of bulk alloys. For (b) samples, the inverse MRs arise primarily from the scattering at the Fe/Cr and Co/Cr interfaces, Inverse MR for X/Y interfaces and X/Y alloys (eg. Fe/Cr and <(Fe)under bar>Cr) arises from the similarity of the matching problem of X and Y d levels at interfaces and in alloys. For all (X) under bar Y the CIP-MR was negative confirming that CIP-MR is strongly influenced by channeling effect and current inhomogenieties. (C) 1996 Elsevier Science B.V. All rights reserved.
Upper critical field of granular SnGe samples near the superconductor-to-insulator transition
(2005-06-01)
Lin, PJ
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Hsu, SY
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電子物理學系
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Department of Electrophysics
We have measured the upper critical field, H-c2(T), in granular SnGe samples with normal state resistivities, rho(N), that range from 0.3 m Omega cm to 0.5 Omega cm. The samples demonstrate an evolution from superconducting to insulating in transport with increasing disorder. The temperature dependence of H-c2 shows a clear change in curvature between high rho(N) and intermediate rho(N) samples differing from the experimental results by Deutscher et al.. Our data is analyzed in terms of Ginzburg-Landau theory and grain structure induced disorder effect. The result is similar to the observation in high T-c superconductors that anisotropy induced fluctuation effect play an important role.