Browsing by Issue Date, starting with "2000-01-15"

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Interaction of phosphine with Si(100) from core-level photoemission and real-time scanning tunneling microscopy
(2000-01-15)
Lin, DS
;
Ku, TS
;
Chen, RP
;
物理研究所
;
Institute of Physics
In this paper, we investigate the interaction of phosphine (PH3) on the Si(100)-2 x 1 surface at temperatures between 635 and 900 K. The hydrogen desorption, growth mode, surface morphology, and chemical composition and ordering of the surface layer are examined by synchrotron radiation core-level photoemission and real-time high-temperature scanning tunneling microscopy. The P 2p core-level spectra indicate that decomposition of PHn is complete above similar to 550 K and the maximum P coverage is strongly influenced by the growth temperature, which governs the coverage of H-terminated sites. The scanning tunneling microscopy (STM) images taken at real time during PH3 exposure indicate that a surface phosphorus atom readily and randomly displaces one Si atom from the substrate. The ejected Si diffuses, nucleates, and incorporates itself into islands or step edges, leading to similar growth behavior as that found in Si chemical vapor deposition. Line defects both perpendicular and parallel to the dimer rows are observed on the nearly P-saturated surface. Perpendicular line defects act as a strain relief mechanism. Parallel line defects result from growth kinetics. STM images also indicate that incorporating a small amount of phosphorus eliminates the line defects in the Si(100)-2 x n surface.
An inventory model with deteriorating items under inflation when a delay in payment is permissible
(2000-01-15)
Liao, HC
;
Tsai, CH
;
Su, CT
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
This study develops an inventory model for initial-stock-dependent consumption rate when a delay in payment is permissible. In the inventory model, shortages are not allowed. The effect of the inflation rate, deterioration rate, initial-stock-dependent consumption rate and delay in payment are discussed. In the study, mathematical models are also derived under two different circumstances, i.e., Case I: The credit period is less than or equal to the cycle time for settling the account; and Case II: The credit period is greater than the cycle time for settling the account. Besides, expressions for an inventory system's total cost are derived for these two cases. Moreover, a computational procedure and GINO (Lasdon et al., ACM Transactions Mathematical Software 4 (1978) 34-50) are proposed to obtain the optimal order size and cycle time. The results can help managers determine the optimal total cost. Finally, a numerical example demonstrates the applicability of the proposed model. (C) 2000 Elsevier Science B.V. All rights reserved.
Photoemission, near-edge x-ray-absorption spectroscopy, and low-energy electron-diffraction study of C-60 on Au(111) surfaces
(2000-01-15)
Tzeng, CT
;
Lo, WS
;
Yuh, JY
;
Chu, RY
;
Tsuei, KD
The geometric and electronic structures of C-60 adsorption on Au(111) surfaces have been studied py low-energy electron diffraction (LEED), angle-resolved photoemission, and near-edge x-ray-absorption spectroscopy. An irreversible structural transition of the C-60 overlayer on Au(111) was observed by LEED upon successive annealing. These structures are 38 x 38 "in phase," R14 degrees and (2 root 3 x 2 root 3)R30 degrees, with the latter phase predominating after annealing to 350 degrees C. Valence-band photoemission spectra reveals a state right below the Fermi level for an annealed, ordered monolayer. This peak disperses across the Fermi energy that indicates the C-60 overlayer becomes metallic. Its intensity shows a resonance that primarily follows the behavior of highest occupied molecular orbitals, identified unambiguously as lowest unoccupied molecular orbitals (LUMO's) filled by charge transfer from the substrate. An asymmetric distribution of LUMO charge is observed. The thermal-desorption energy of the monolayer is estimated from annealing experiments to be 1.9 eV, which is 0.5 eV larger than the desorption energy from multilayers. Comparison with available spectroscopic data indicates that interaction of C-60 with Au(111) is slightly weaker than with Au(110), and much weaker than with Cu(111). The amount of charge transfer estimated from photoemission is 0.8 electrons per C-60 molecule on Au(111), compared to 1.6 electrons on Cu(111). We argue that charge transfer is determined by the bulk sp density of states at the Fermi energy scaled by the size of the C-60 molecule, and also modified by a clean surface electronic structure, and that charge transfer is the dominant interaction in these systems.
An optimal representative set selection method
(2000-01-15)
Lee, JG
;
Chung, CG
;
資訊工程學系
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Department of Computer Science
The optimal representative set selection problem is defined thus: given a set of test requirements and a test suite that satisfies all test requirements, find a subset of the test suite containing a minimum number of test cases that still satisfies all test requirements. Existing methods for solving the representative set selection problem do not guarantee that obtained representative sets are optimal (i.e, minimal). The enhanced zero-one optimal path set selection method [C.G. Chung, J.G. Lee, An enhanced zero-one optimal path set selection method, Journal of Systems and Software, 39(2) (1997) 145-164] solves the so-caned optimal path set selection problem, and can be adapted to solve the optimal representative set selection problem by considering paths as test cases and components to be covered (e.g. branches) as test requirements. (C) 2000 Elsevier Science B.V. All rights reserved.
Physical properties of polar bis-tolane liquid crystals
(2000-01-15)
Wu, ST
;
Hsu, CS
;
Chuang, YY
;
Cheng, HB
;
應用化學系
Several cyano and fluoro bis-tolane liquid crystals were synthesized and their physical properties evaluated. Some of these highly conjugated liquid crystals possess birefringence larger than 0.5 in the visible region. Adding 10% of a binary bis-tolane mixture to a cholesteric display enhances the brightness by more than 20%.
Thin-film transistors with polycrystalline silicon films prepared by two-step rapid thermal annealing
(2000-01-15)
Cheng, HC
;
Huang, CY
;
Wang, FS
;
Lin, KH
;
Tarntair, FG
A novel two-step rapid thermal annealing (RTA) process has been developed to significantly reduce the crystallization time for the solid-phase crystallization (SPC) of amorphous silicon films. In comparison with the conventional SPC processes, it not only keeps a low thermal budget but also achieves a larger poly-Si film grain size than that obtained by one-step RTA, and even as large as that obtained by conventional furnace annealing (CFA). Furthermore, poly-Si thin-film transistors fabricated by such a novel annealing scheme possess electrical characteristics superior to those obtained by one-step RTA and comparable to those obtained by long-time CFA.
Nanometer-scale conversion of Si3N4 to SiOx
(2000-01-17)
Chien, FSS
;
Chang, JW
;
Lin, SW
;
Chou, YC
;
Chen, TT
It has been found that atomic force microscope (AFM) induced local oxidation is an effective way for converting thin (< 5 nm) Si3N4 films to SiOx. The threshold voltage for the 4.2 nm film is as low as 5 V and the initial growth rate is on the order of 10(3) nm/s at 10 V. Micro-Auger analysis of the selectively oxidized region revealed the formation of SiOx. Due to the large chemical selectivity in various etchants and great thermal oxidation rate difference between Si3N4, SiO2, and Si, AFM patterning of Si3N4 films can be a promising method for fabricating nanoscale structures. (C) 2000 American Institute of Physics. [S0003-6951(00)03003-5].
The effects of microcrystalline silicon film structure on low-high-low band-gap thin film transistor
(2000-01-29)
Chang, CY
;
Lee, YS
;
Huang, TY
;
Shih, PS
;
Lin, CW
The effects of hydrogenated microcrystalline silicon (mu c-Si:H) film with various crystalline factors on thin-film transistors (TFTs) with low-high-low band gap structure are studied. Compared to hydrogenated amorphous silicon (a-Si:H) TFT with conventional inverted-stagger structure, the device with mu c-Si:H film of high crystalline factor in the active channel depicts improved interfacial active layer near the gate insulator interface as well as the later-grown bulk active layer, resulting in improved device parameters including field effect mobility, threshold voltage, subthreshold swing and ON-current. While a-Si:H film of low crystalline factor and high-band-gap is proposed for the source and drain offset regions in the new device to prevent the band-to-band tunneling, thus alleviates the high OFF-current inherent in conventional mu c-Si:H thin-film transistors, resulting in an improved ON/OFF current ratio. (C) 2000 Elsevier Science S.A. All rights reserved.
Effect of diatomic islands on step morphological stability of a terrace edge in molecular beam epitaxy (vol 353, pg 174, 1999)
(2000-01-31)
Lin, SP
;
Hwang, CC
;
Chu, HS
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機械工程學系
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Department of Mechanical Engineering
Mechanistic study of beta-xylosidase from Trichoderma koningii G-39
(2000-02-01)
Li, YK
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Yao, HJ
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Pan, IH
;
應用化學系
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Department of Applied Chemistry
The catalytic mechanism of the beta-xylosidase purified from the culture filtrate of Trichoderma Koningii G-39 was investigated. By NMR spectroscopy, the stereochemistry of the enzyme catalyzing the hydrolysis of 2,4,dinitrophenyl and p-nitrophenyl-beta-D-xylosides was found unequivocally to involve retention of the anomeric configuration, Based on the k(cat) values of a series of arylxylosides with leaving group pK(a)s in the range of 4-10, an extended Bronsted plot was constructed with a slope (beta(Ig)) near zero. Enzymatic hydrolysis of aryl-beta-D-xylosides in acetate buffer (pH 4.0) containing 3 or 5% methanol showed a constant product ratio (methylxyloside/xylose), indicating the presence of a common intermediate, probably the xylosyl-enzyme intermediate. In the presence of DTT, the k(cat) values of p-cyanophenyl-beta-D-xylopyranoside and p-nitrophenyl-beta-xylopyranoside increased greatly. A two-step mechanism involving the formation and breakdown of the xylosyl-enzyme intermediate was therefore proposed. The rate-limiting step is the breakdown of the intermediate. The secondary deuterium kinetic isotope effect (k(H)/k(D)) measured for 2,4-dinitrophenyl-beta-D-xyloside was 1.02+/-0.01, suggesting that the transition state for breakdown of the xylosyl-enzyme intermediate is S(N)2-like.
HTS surface wave resonators
(2000-02-01)
Melkov, GA
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Egorov, YV
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Ivanjuta, OM
;
Malyshev, VY
;
Zeng, HK
A novel class of surface wave high-temperature superconductivity (HTS) resonators was investigated. The resonator consists of HTS film and one or two dielectric plates. One of the dielectric plates may be the HTS film substrate. Theoretical analysis of the resonator structure was carried out using the partial region method, with the 20 lowest waves being considered in every region. The resonant frequencies, quality of oscillations, and the field and current distributions were calculated. It was shown that there is a high-density and homogeneous microwave current flowing on the film surfaces. Experimental measurements carried out in the 3-cm wavelength range demonstrate good agreement with simulated data.
Effects of polysilicon gate doping concentration on plasma charging damage in ultrathin gate oxides
(2000-02-01)
Chen, CC
;
Lin, HC
;
Chang, CY
;
Huang, TY
;
Chien, CH
Effects of poly-gate doping concentration on plasma charging damage in ultrathin gate oxides were investigated. While the charge-to-breakdown (Q(bd)) value under gate injection stress polarity (-V-g) is independent of the doping concentration, eb, under substrate injection stress polarity (+V-g) shows a noticeable improvement with increasing doping concentration. However, our results show that plasma-induced oxide degradation is actually aggravated with increasing poly-gate doping concentration. These seemingly inconsistent observations can be explained by the lowering of plasma charging potential in the case of insufficient poly-gate doping. (C) 1999 The Electrochemical Society. S1099-0062(99)10-079-8. All rights reserved.
Fast VQ encoding by an efficient kick-out condition
(2000-02-01)
Wu, KS
;
Lin, JC
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資訊工程學系
;
Department of Computer Science
A new fast approach to the nearest codeword search using a single kick-out condition is proposed. The nearest codeword found by the proposed approach is identical to the one Found by the full search, although the processing time is much shorter. The principle is to bypass those codewords which satisfy the proposed kick-out condition without the actual (and time-consuming) computation of the distortions from the bypassed codewords to the query vector. Due to the efficiency and simplicity of the proposed condition, a considerable saving of the central processing unit time needed to encode a data set (using a given codebook) can be achieved. Moreover, the memory requirement is low. Comparisons with some recent works are included to show these two benefits.
Two-dimensional beam-scanning linear active leaky-wave antenna array using coupled VCOs
(2000-02-01)
Hu, CC
;
Jou, CF
;
Wu, JJ
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傳播研究所
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Institute of Communication Studies
An active phased-array design for electronic two-dimensional beam scanning using a phase-shifterless linear one-dimensional active leaky-wave antenna array is demonstrated. The varactor-tuned voltage-controlled oscillators (VCOs) and coupling network are implemented in this array. Three coupling networks are designed and compared for optimum coupling strength between each VCO element. The measured pattern of a 4 x 1 active leaky-wave antenna array shows that the main beam can be continuously scanned from 68 degrees to 40 degrees in elevation, as the frequency varies from 8.24GHz to 9.15GHz. This is equivalent to over 10% electronic tuning bandwidth. By tuning the free-running frequencies of the end elements, the main beam can be continuously scanned from -26 degrees to +10 degrees from broadside with azimuth symmetry in a conical scan manner.
Optimal multiple stage expansion of competence set
(2000-02-01)
Li, JM
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Chiang, CI
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Yu, PL
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運輸與物流管理系註：原交通所+運管所
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Department of Transportation and Logistics Management
In this paper, we consider the expansion processes of competence sets which have asymmetric cost functions, intermediate skills, and compound skills; among the skills, cyclic connections are possible. We introduce the concept of the stage expansion process (SEP) of the competence set, and provide mathematical programming methods to find a minimal cost SEP and the ordering of expansion. (C) 2000 Elsevier Science B.V. All rights reserved.
An early vision-based snake model for ultrasound image segmentation
(2000-02-01)
Chen, CM
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Lu, HHS
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Lin, YC
;
統計學研究所
;
Institute of Statistics
Due to the speckles and the ill-defined edges of the object of interest, the classic image-segmentation techniques are usually ineffective in segmenting ultrasound (US) images. In this paper, we present a new algorithm for segmenting general US images that is composed of two major techniques; namely, the early-vision model and the discrete-snake model, By simulating human early vision, the early-vision model can capture both grey-scale and textural edges while the speckle noise is suppressed. By performing deformation only on the peaks of the distance map, the discrete-snake model promises better noise immunity and more accurate convergence. Moreover, the constraint for most conventional snake models that the initial contour needs to be located very close to the actual boundary has been relaxed substantially. The performance of the proposed snake model has been shown to be comparable to manual delineation and superior to that of the gradient vector flow (GVF) snake model. (C) 2000 World Federation for Ultrasound in Medicine & Biology.
Enhancement of barrier properties in chemical vapor deposited TiN employing multi-stacked Ti/TiN structure
(2000-02-01)
Chang, TC
;
Liu, PT
;
Yang, YL
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Hu, JC
;
Sze, SM
A novel multi-stacked Ti/TiN structure was proposed to enhance the barrier properties of chemical vapor deposited TiN film. Both the chlorine content and the resistivity of the multi-stacked Ti/TiN films are significantly decreased when compared with a single layer of chemical vapor deposited (CVD) TiN film with the same thickness. Secondary ion mass spectrometry (SIMS) data showed that Ti atom distribution is fairly uniform to fill the grain boundary of TiN film. Therefore, the leakage current resulted from junction spiking was further reduced by the grain boundary effects when employing multi-stacked Ti/TiN as diffusion barrier layer instead of a single layer of TiN film.
Joint wavelet and spatial transformation for digital watermarking
(2000-02-01)
Tsai, MJ
;
Yu, KY
;
Chen, YZ
;
資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
A new watermarking scheme which incorporates wavelet and spatial transformation has been del eloped for digital images in this paper. This algorithm utilizes the wavelet multiresolutional structure to construct the image frequency components and the chaotic transformation as two dimensional integer vector generators for spatial transform to select the location during the watermark embedding. To efficiently embed the watermark; within the image without the loss of image quality and provide the robustness for the watermark detection under attacks, a modular based spatial threshold and adjustment scheme of the wavelet coefficients has been developed in this research. Unlike other watermarking schemes which usually rely on significantly large amount of side information for watermark detection, our algorithm need only few key parameters to detect the watermark with meaningful content. Compared with some known approaches of watermarking schemes, this algorithm results in superior robustness and information protection fur beeping watermark intact under image processing attacks like image: compression.
Step-by-step decoding algorithm for Reed-Solomon codes
(2000-02-01)
Chen, TC
;
Wei, CH
;
Wei, SW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A new step-by-step decoding algorithm for decoding Reed-Solomon codes over GF(2(m)) is presented. Based on several properties of the syndrome matrices, the new step-by-step decoding algorithm can directly determine whether every received symbol is an error locator, The detection of error location is based only on the determinant of a v x v syndrome matrix, where v is the number of errors. When an error location is found, its corresponding error value can also be determined by performing a determinant division operation between two syndrome matrices. The new decoding algorithm can significantly reduce computation complexity and improve the decoding speed compared with the conventional step-by-step decoding algorithm.
Synthesis of laterally substituted bistolane liquid crystals
(2000-02-01)
Hsu, CS
;
Shyu, KF
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Chuang, YY
;
Wu, ST
;
應用化學系
Methods for synthesizing bistolane liquid crystal materials with lateral methyl and ethyl substituents are presented. Some of the bistolanes are nematic at room temperature. These highly conjugated mesogens exhibit wide nematic ranges, small enthalpies of fusion, high birefringence and modest viscosity. Their potential applications for flat panel displays employing light scattering or Bragg reflection and for infrared optically phased arrays are foreseeable.