Browsing by Issue Date, starting with "2000-11-06"

Now showing 1 - 20 of 77973

Carrier distribution and relaxation-induced defects of InAs/GaAs quantum dots
(2000-11-06)
Wang, JS
;
Chen, JF
;
Huang, JL
;
Wang, PY
;
Guo, XJ
The carrier distribution and defects have been investigated in InAs/GaAs quantum dots by cross-sectional transmission electron microscopy (XTEM), capacitance-voltage, and deep level transient spectroscopy. Carrier confinement is found for 1.1- and 2.3-monolayer-(ML)-thick InAs samples. For 2.3 ML sample, XTEM images show the presence of defect-free self-assembled quantum dots. With further increase of the InAs thickness to 3.4 ML, significant carrier depletion caused by the relaxation is observed. In contrast to 1.1 and 2.3 ML samples in which no traps are detected, two broad traps and three discrete traps at 0.54, 0.40, and 0.34 eV are observed in 3.4 ML sample. The traps at 0.54 and 0.34 eV are found to be similar to the traps observed in relaxed In0.2Ga0.8As/GaAs single quantum well structures. By comparing with the XTEM images, the trap at 0.54 eV is identified to be the relaxation-induced dislocation trap in the GaAs layer. (C) 2000 American Institute of Physics. [S0003-6951(00)02245-2].
Hyperbranched poly(aryl ether oxazole)s: Synthesis, characterization, and modification
(2000-11-14)
Gong, ZH
;
Leu, CM
;
Wu, FI
;
Shu, CF
;
應用化學系
In this paper the synthesis and characterization of a hyperbranched poly(aryl ether oxazoIe) with terminal phenolic groups are described. An ABB' monomer containing a pair of phenolic groups and an aryl fluoride which is activated toward displacement by the attached oxazole ring was prepared. The nucleophilic substitution of the fluoride with the phenolic group leads to the formation of ether linkage and subsequently the hyperbranched poly(aryl ether oxazole) P1. As determined by a combination of model compound studies and H-1 NMR integration experiments, the degree of branching of PI is approximately 50%. The polymer P1 is thermally stable and readily soluble in polar organic solvents. The terminal phenolic groups in P1 were easily functionalized, yielding hyperbranched polymers with a variety of functional chain ends. Physical properties, such as the glass transition temperature and the solubility of the hyperbranched poly(aryl ether oxazole)s, depended significantly on the nature of the chain ends.
Mechanical properties of clay-polyimide (BTDA-ODA) nanocomposites via ODA-modified organoclay
(2000-11-15)
Tyan, HL
;
Wei, KH
;
Hsieh, TE
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Clay-polyimide [3,3', 4,4'-benzophenone tetracarboxylic dianhydride-4,4'-oxydianiline (BTDA-ODA)] nanocomposites were synthesized from ODA-modified montmorillonite (organoclay) and poly(amic acid). The layered silicates of organoclay were intercalated by polyimide (BTDA-ODA), as confirmed by X-ray diffraction and by transmission electron microscopy, and the tensile mechanical properties of the nanocomposites were measured. It was found that the modulus and the maximum stress of these organoclay/BTDA-ODA nanocomposites were much higher than those of pure BTDA-ODA: a twofold increase in the modulus and a one-half-fold increase in the maximum stress in the case of 7/93 organoclay-BTDA-ODA. In addition, the elongation-for-break of organoclay/BTDA-ODA nanocomposites is even slightly higher than that of pure BTDA-ODA, which is a sharp contrast to that of conventional inorganics-filled polymer composites. (C) 2000 John Wiley & Sons, Inc.
Weak-field expansion for processes in a homogeneous background magnetic field
(2000-11-15)
Chyi, TK
;
Hwang, CW
;
Kao, WF
;
Lin, GL
;
Ng, KW
The weak-field expansion of the charged fermion propagator under a uniform magnetic field is studied. Starting from Schwinger's proper-time representation, we express the charged fermion propagator as an infinite series corresponding to different Landau levels. This infinite series is then reorganized according to the powers of the external field strength B. For illustration, we apply this expansion to gamma --> nu<()over bar> and nu --> nu gamma decays, which involve charged fermions in the internal loop. The leading and subleading magnetic-field effects to the above processes are computed.
Cycle-symmetric matrices and convergent neural networks
(2000-11-15)
Shih, CW
;
Weng, CW
;
應用數學系
;
Department of Applied Mathematics
This work investigates a class of neural networks with cycle-symmetric connection strength. We shall show that, by changing the coordinates, the convergence of dynamics by Fiedler and Gedeon [Physica D 111 (1998) 288] is equivalent to the classical results. This presentation also addresses the extension of the convergence theorem to other classes of signal functions with saturations. In particular, the result of Cohen and Grossberg [IEEE Trans. Syst. Man Cybernet. SMC-13 (1983) 815] is recast and extended with a more concise verification. (C) 2000 Elsevier Science B.V. All rights reserved.
Application of Grey theory and multiobjective programming towards airline network design
(2000-11-16)
Hsu, CI
;
Wen, YH
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
Airline network design encompasses decisions on an airline network shape and route flight frequencies. Related investigations handle the trade-off between enhancing passengers' service levels and lowering the airline's operating costs by applying deterministic optimization methods. In contrast with other conventional methods, Grey theory is a feasible mathematical device capable of forecasting airline traffic with minimum data and resolving problems containing uncertainty and indetermination. In the light of these developments, this study develops a series of models capable of forecasting airline city-pair passenger traffic, designing a network of airline routes and determining Eight frequencies on individual routes by applying Grey theory and multiobjective programming. A case study demonstrates the feasibility of applying the proposed models. Results in this study not only confirm the practical nature of the preposed models, but also their ability to provide high flexibility in decision making for airlines. (C) 2000 Elsevier Science B.V. All rights reserved.
Thermal stability of Cu/Ta/GaAs multilayers
(2000-11-20)
Chen, CY
;
Chang, L
;
Chang, EY
;
Chen, SH
;
Chang, DF
Copper metallization for GaAs was evaluated by using Cu/Ta/GaAs multilayers for its thermal stability. A thin Ta layer of 40 nm was sputtered on the GaAs substrate as the diffusion barrier before copper film metallization. As judged from sheet resistance, x-ray diffraction, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films with GaAs were very stable up to 500 degreesC without migration into GaAs. After 550 degreesC annealing, the interfacial mixing of Ta with GaAs substrate occurred, resulting in the formation of TaAs2. At 600 degreesC annealing, the reaction GaAs with Ta and Cu formed TaAs, TaAs2, and Cu3Ga, resulting from Cu migration and interfacial instability. (C) 2000 American Institute of Physics. [S0003-6951(00)03047-3].
Low-resistance ohmic contacts on p-type GaN using Ni/Pd/Au metallization
(2000-11-20)
Chu, CF
;
Yu, CC
;
Wang, YK
;
Tsai, JY
;
Lai, FI
In this letter, a low-resistance ohmic contact on p-type GaN using an alloy of Ni/Pd/Au is reported. The Mg doped p-type GaN samples were grown by metalorganic chemical vapor deposition with a carrier concentration of 4.1x10(17) cm(-3). The as-grown Mg doped samples were deposited with Ni (20 nm)/Pd (20 nm)/Au (100 nm) and then annealed in air, nitrogen, and oxygen ambient conditions at different annealing temperatures ranging from 350 to 650 degreesC. Linear I-V ohmic characteristics were observed with specific resistance as low as 1.0x10(-4) Omega cm(2) for the samples annealed in oxygen atmosphere. Similar contact metal composition was also deposited on Be-implanted p-type GaN samples with a carrier density of 8.1x10(19) cm(-3). Without further annealing process, the samples show good ohmic contact with a lowest specific resistance of 4.5x10(-6) Omega cm(2). (C) 2000 American Institute of Physics. [S0003-6951(00)01847-7].
Low-complexity code tracking loop with chip-level differential detection for DS/SS receivers
(2000-11-23)
Lin, JC
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
A new code tracking loop is proposed for direct-sequence spread-spectrum communications. The main features of such a technique are its lower complexity together with its good tracking performance. Analytical expressions for the error characteristic are derived and timing jitter is evaluated by computer simulation.
As-quenched microstructures of Cu-14.2Al-xNi alloys
(2000-11-27)
Tan, J
;
Liu, TF
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Characterization of crystallization in syndiotactic polystyrene thin film samples
(2000-11-28)
Wu, HD
;
Wu, ID
;
Chang, FC
;
應用化學系
;
Department of Applied Chemistry
The observation of the competition and suppression for stimulated Raman scattering near the potassium 4S-5P resonance
(2000-11-28)
Wang, HW
;
Lu, MH
;
光電工程學系
;
Department of Photonics
The competition of stimulated Raman scattering (SRS) between 4S-(5P)-5S and 4S-(3D)-5S channels has been observed as a laser is tuned near the 4S-5P resonance in potassium vapour. The experimental results show that SRS only occurs in the 4S-(5P)-5S channel. In this Raman scattering, suppression of the amplified spontaneous emission (ASE) (5S-4P) has been observed, The influence of the four-wave mixing (FWM) processes on the SRS is discussed. In the 4S-(5P)-3D channel, in the backward direction no detectable emission corresponding to SRS (4S-(5P)-3D) has been observed, so the forward (5P)-3D emission should be FWM, not SRS. The ASE (3D-4P) arises from the ASE (5P-3D), which can be observed in the backward direction.
Effect of mechanical properties using different filler metals on wide-clearance activated-diffusion-brazed Ni-based superalloy
(2000-12-01)
Su, CY
;
Chou, CP
;
Chang, WJ
;
Liu, MH
;
機械工程學系
The investigation of mechanical properties and failure mechanism of activated-diffusion-brazed (ADB) joints in IN-738 plate were conducted. Joints of this type, which had wide clearance, were formed using the brazing alloys Nicrobraz 150 and DF4B, The microstructural characterization showed that chromium borides with a blocky morphology were present in joints associated with the two brazing alloys. A major difference in matrix phase chemistry was observed, however, for the two brazing alloys, e.g., an Ni-B eutectic phase was observed in Nicrobraz 150, but DF4B exhibited a coarsened gamma prime (gamma) phase and an absence of a nickel boride matrix phase, Results of tensile test showed that ADB specimens using DF4B brazing alloy exhibited 95% nominal tensile strength of IN-738 base materials. Fracture cracks in the joint area mere initiated and confined to dispersed chromium boride sites. However, tensile test of ADB specimens using Nicrobraz 150 showed poor tensile properties at all testing temperatures, and their fractures were initiated at a brittle nickel boride site and propagated along the weak-bonded interface between the Ni-B eutectic phase and base materials.
On assessing the association for bivariate current status data
(2000-12-01)
Wang, WJ
;
Ding, AA
;
統計學研究所
;
Institute of Statistics
Assuming that the two failure times of interest with bivariate current status data follow a bivariate copula model, we propose a two-stage estimation procedure to estimate the association parameter which is related to Kendall's tau. Asymptotic properties of the proposed semiparametric estimator show that, although the first-stage marginal estimators have a convergence rate of only n(1/3), the resulting parameter estimator still converges to a normal random variable with the usual n(1/2) rate. The variance of the proposed estimator can be consistently estimated. Simulation results are presented, and a community-based study of cardiovascular diseases in Taiwan provides an illustrative example.
The characterization of nitrogen content, diamond-like carbon field emission arrays using a magnetic filtered arc method
(2000-12-01)
Chen, CF
;
Shen, CH
;
Lin, CL
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Uniform and large area pyramid-shape diamond-like carbon (DLC) field emission arrays are successfully deposited using the filtered are deposition (FAD) system. Nitrogen gas serves as the dopant source to deposit the diamond-like carbon films on the inverted pyramid-shape SiO2 substrates. Experimental results indicate that the current-voltage (I-V) value of field emission arrays is closely related to the diamond-like carbon film quality. The amount of N-2 content in the film influences the composition of the diamond-like carbon, sp(2) bonding carbon and graphite. It was found that the sp? bonding carbon content of the diamond-like carbon increases with increasing N-2 doping. With nitrogen doping, the emission anode current of the diamond-like carbon film significantly increases, eventually reaching 142 muA at a voltage of 30 V, at heavily N-doped concentrations (10 seem), when the films reach a high defect density. (C) 2000 Elsevier Science B.V. All rights reserved.
High-performance and high-reliability 80-nm gate-length DTMOS with indium super steep retrograde channel
(2000-12-01)
Chang, SJ
;
Chang, CY
;
Chen, CM
;
Chao, TS
;
Lee, YJ
In this paper, we demonstrate for the first time a high-performance and high-reliability 80-nm gate-length dynamic threshold voltage MOSFET (DTMOS) using indium super steep retrograde channel implantation. Due to the steep indium super steep retrograde (In-SSR) dopant profile in the channel depletion region, the novel In-SSR DTMOS features a low V-th in the off-state suitable for low-voltage operation and a large body effect to fully exploit the DTMOS advantage simultaneously, which is not possible with conventional DTMOS, As a result, excellent 80-nm gate length transistor characteristics with drive current as high as 348 muA/mum (off-state current 40 nA/mum), a record-high Gm = 1022 mS/mm, and a subthreshold slope of 74 mV/dec, are achieved at 0.7 V operation. Moreover, the reduced body effects that have seriously undermined conventional DTMOS operation in narrow-width devices are alleviated in the In-SSR DTMOS, due to reduced indium dopant segregation. Finally, it was found for the first time that hot-carrier reliability is also improved in DTMOS-mode operation, especially for In-SSR DTMOS.
Modified stochastic Luenberger observers
(2000-12-01)
Hsieh, CS
;
Chen, FC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
A modified stochastic Luenberger observer (MSLO) structure is proposed to recover the optimal performance of the coventional SLO for obtaining full-state estimates in linear discrete-time stochastic systems. The optimal MSLO (OMSLO) which gives the MMSE estimates is derived by using the general two-stage Kalman filter. A reduced-order form of the OMSLO is also proposed for systems having singular measurement noises. The connection between the OMSLO and the optimal minimal-order observer of Leondes and Novak is also shown. (C) 2000 Elsevier Science Ltd. All rights reserved.
RTE lag in diffractive optical element etching
(2000-12-01)
Ting, JH
;
Su, JC
;
Su, SY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this study, the pattern of a 4 mm diameter diffractive optical element with linewidth ranging from 12 to 0.5 mum was adopted. With the SiO2 layer as the etch hard mask, silicon was etched based on HBr chemistry with additions of O-2 and SF6 . The effects of O-2 content on the sidewall anisotropy, etch rate, and etch selectivity over the SiO2 mask were also examined. The RIE lag, where etching of a small trench (hole) lags behind a large trench (hole), was investigated to produce an optimum aspect ratio for each zone of the diffractive optical element. The regression relation of the etch depth versus zone width was determined as a guideline for the feasibility of this method. (C) 2000 Elsevier Science B.V. All rights reserved.
A causal multicast protocol for mobile distributed systems
(2000-12-01)
Chi, KH
;
Yen, LH
;
Tseng, CC
;
Huang, TL
;
資訊工程學系
Causal message ordering in the context of group communication ensures that ail the message receivers observe consistent ordering of events affecting a group as a whole. This paper presents a scalable causal multicast protocol for mobile distributed computing systems. In our protocol, only a Dart of the mobility agents in the system is involved in group computations and the resulting size of control information in messages can be kept small. Our protocol can outperform qualitatively the counterparts in terms of communication overhead and hand-off complexity An analytical model is also developed to evaluate our proposal. The performance results show that the proposed protocol is promising.
Hot-electron relaxation via optical phonon emissions in GaAs/AlxGa1-xAs quantum well structures: dependence upon the alloy composition and barrier width
(2000-12-01)
Sun, KW
;
Chang, HY
;
Wang, CM
;
Wang, SY
;
Lee, CP
We present a systematic investigation of the dependence of the hot-electron-optical-phonon interactions on Al composition and barrier width in GaAs/AlxGa1-xAs MQW structures. Raman scattering measurements at 15 K are presented for samples with different barrier widths and Al composition. The optical phonon energies emitted by the photoexcited electrons in quantum wells were also determined by using hot-electron-neutral acceptor luminescence techniques. It is shown that the relaxation of hot electrons in the quantum wells is dominated by the GaAs LO phonon emission for small x, but by AlAs-like LO phonons for larger Al composition. For samples with larger barriers, the electrons in the GaAs layer relax mostly through the AlAs-like optical phonon emission. However, in samples with smaller barriers, the relaxation of hot electrons is dominated by the GaAs optical phonon emission.