Browsing by Issue Date, starting with "2008-03-31"

Now showing 1 - 20 of 55883

Phase transformation and optical characteristics of porous germanium thin film
(2008-03-31)
Ko, T. S.
;
Shieh, J.
;
Yang, M. C.
;
Lu, T. C.
;
Kuo, H. C.
In this study, we proposed a method to prepare GeO2 by treating porous Ge thin film with thermal annealing in O-2 ambient. After annealing, the morphological transformation from porous thin film to an island structure was observed. The crystallization and composition of the porous Ge thin film prepared using different annealing time in O-2, ambient were confirmed by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectra. Initial Ge composition was gradually oxidized to GeO2 with increasing annealing time. Comparing the photoluminescence (PL) results between Ge and GeO2, it was found that the visible photoluminescence originated from the germanium oxide. Photoluminescence measurements obtained at different temperatures exhibited a maximum integrated PL intensity at around 200 K. A possible explanation for this behavior might be the competition between radiative recombination and nonradiative hopping process. (C) 2007 Elsevier B.V. All rights reserved.
Chirp and error rate analyses of an optical-injection gain-switching VCSEL based all-optical NRZ-to-PRZ converter
(2008-03-31)
Lin, Chia-Chi
;
Kuo, Hao-Chung
;
Peng, Peng-Chun
;
Lin, Gong-Ru
;
交大名義發表
Optically injection-locked single-wavelength gain-switching VCSEL based all-optical converter is demonstrated to generate RZ data at 2.5 Gbit/s with bit-error-rate of 10(-9) under receiving power of -29.3 dBm. A modified rate equation model is established to elucidate the optical injection induced gain-switching and NRZ-to-RZ data conversion in the VCSEL. The peak-to-peak frequency chirp of the VCSEL based NRZ-to-RZ is 4.5 GHz associated with a reduced frequency chirp rate of 178 MHz/ps at input optical NRZ power of -21 dBm, which is almost decreasing by a factor of 1/3 comparing with chirp on the SOA based NRZ-to-RZ converter reported previously. The power penalty of the BER measured back-to-back is about 2 dB from 1 Gbit/s to 2.5 Gbit/s. (c) 2008 Optical Society of America.
Reliable tree-type passive optical networks with self-restorable apparatus
(2008-03-31)
Yeh, Chien Hung
;
Shih, Fu-Yuan
;
Chang, Gee-Kung
;
Chi, Sien
;
光電工程學系
We propose and investigate a simply self-restored tree-type time-division-multiplexed passive optical network (TDM-PON) with duplex fiber system against the fiber failure. The new proposed optical line terminal (OLT), optical network unit (ONU), and remote node (RN) can be used to prevent and protect the occurrence of fiber failure in the self-protected tree-type PON. The protection and restoration time of the access network can be archived within 7 ms in this experiment. In addition, the performances of data traffic for the fiber access network are also analyzed and discussed. (C) 2007 Optical Society of America.
Performance enhancement of excimer laser crystallized poly-Si thin film transistors with fluorine implantation technology
(2008-03-31)
Tu, Chun-Hao
;
Chang, Ting-Chang
;
Liu, Po-Tsun
;
Yang, Che-Yu
;
Feng, Li-Wei
Polycrystalline silicon thin film transistors (poly-Si TFTs) with the ion implantation of fluorine elements were investigated in this study. The electrical performance and reliability were reported comprehensively. Experimental work has shown the electrical characteristics of excimer laser crystallized F-ions-implanted poly-Si TFTs are improved effectively, especially for field effect mobility. It is also found that the fluorine piled up at the poly-Si interface during thermal annealing, for the TFT fabricated without a prior deposition of pad oxide. The stronger Si-F bonds replace the Si-Si/Si-H, leading to the superior electrical reliability. However, the dose of F ions is critical in poly-Si, or the electrical characteristics of TFT devices will be degraded. (c) 2007 Published by Elsevier B.V.
Anomalous magnetic ordering in b-axis-oriented orthorhombic HoMnO(3) thin films
(2008-03-31)
Lin, T. H.
;
Hsieh, C. C.
;
Shih, H. C.
;
Luo, C. W.
;
Uen, T. M.
Orthorhombic HoMnO(3) films with well-aligned crystallographic orientations were deposited on LaAlO(3)(110) single crystal substrates by using pulsed laser deposition. The nearly perfect b-axis-oriented films provide the opportunity of investigating the orientation-dependent physical property of this material. The temperature dependent magnetization evidently displays an antiferromagnetic ordering near 42 K, irrespective to the direction of applied field. Furthermore, the theoretically expected lock-in transition was clearly observed at around 30 K when field was applied along the c axis and was undetectable along the a and b axes. The 30 K transition was suppressed to 26 K when the applied field increased from 100 to 500 Oe. (C) 2008 American Institute of Physics.
Synthesis of carbon hollow spheres and particles from CCl4 and Mo
(2008-03-31)
Chien, Chun-Hsiung
;
Sheng, Pei-Sun
;
Wang, Chia-Hsi
;
Huang, Chi-Hao
;
Lin, Huang-Kai
Carbon materials with different morphology were prepared by reacting CCl4 and Mo at 873-1173 K. At 873-973 K, hollow spheres (diameter: 1-3 mu m, shell thickness: 50 nm) were obtained. At 1073 K, particles (diameter: 50-100 nm) encapsulated in spherical shells (diameter: 1-5 mu m) were collected. At H 73 K, formation of particles (diameter: 200-300 nm) was observed. Mo acted as a reagent to remove chlorine atoms from the carbon source and a template for the formation of the spherical structures. We propose that reaction temperature and polymerization of chlorinated species formed from the pyrolysis of CCl4 affect the morphology of carbon products greatly. (C) 2007 Elsevier B.V. All rights reserved.
Huge positive magnetoresistance in a gated AlGaAs/GaAs high electron mobility transistor structure at high temperatures
(2008-03-31)
Liang, C. -T.
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Tseng, Yen Shung
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Wu, Jau-Yang
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Lin, Sheng-Di
;
Yang, Chun-Kai
Magnetoresistivity measurements on a gated AlGaAs/GaAs high electron mobility transistor (HEMT) structure were performed at high temperatures T. By changing the applied gate voltage V(g), we can investigate the observed huge positive magnetoresistance (PMR) at different effective disorder and density inhomogeneity within the same HEMT structure. The observed PMR value increases with increasing disorder in the depletion mode (V(g)<= 0). Moreover, the PMR value is not limited by the quality of the HEMT structure at T=80 K. Such results pave the way for low-cost, high-throughput GaAs-based HEMT fabrication for future magnetic sensing and recording devices fully compatible with the mature HEMT technology. (C) 2008 American Institute of Physics.
Improved shrinkage estimation of squared multiple correlation coefficient and squared cross-validity coefficient
(2008-04-01)
Shieh, Gwowen
;
管理科學系
;
Department of Management Science
The sample squared multiple correlation coefficient is widely used for describing the usefulness of a multiple linear regression model in many areas of science. In this article, the author considers the problem of estimating the squared multiple correlation coefficient and the squared cross-validity coefficient under the assumption that the response and predictor variables have a joint multinormal distribution. Detailed numerical investigations are conducted to assess the exact bias and mean square error of the proposed modifications of established estimators. Notably, the positive-part Pratt estimator and the synthesis of Browne and positive-part Pratt estimators are recommended in the estimation of squared multiple correlation coefficient and squared cross-validity coefficient, respectively, for their overall advantages of incurring the least amount of statistical discrepancy and computational requirement.
Determining vortex chirality in ferromagnetic ring by lateral nonlocal spin valve
(2008-04-01)
Chen, D. C.
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Yao, Y. D.
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Wu, J. K.
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Yu, C.
;
Lee, S. F.
We demonstrate detecting chirality of vortex state in a magnetic ring by lateral nonlocal spin-valve (NLSV) measurement. A Permalloy (Py) ring, a Py narrow wire, and copper contacts were used as spin injector, detector, and the normal-metal diffusive channel, respectively. By comparing the anisotropic magnetoresistance loop of the individual ring with NLSV loop, the vortex chirality and the related switching field of the ring can be determined. Both onion-to-vortex transition field and vortex chirality were found to alternate in both the same and different current probe arrangements on the magnetic ring. (C) 2008 American Institute of Physics.
Effects of interfacial sulfidization and thermal annealing on the electrical properties of an atomic-layer-deposited Al(2)O(3) gate dielectric on GaAs substrate
(2008-04-01)
Cheng, Chao-Ching
;
Chien, Chao-Hsin
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Luo, Guang-Li
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Yang, Chun-Hui
;
Chang, Ching-Chih
In this study we investigated the interfacial chemistry occurring between an atomic-layer-deposited Al(2)O(3) high-k film and a GaAs substrate and the impact of sulfidization and thermal annealing on the properties of the resultant capacitor. We observed that sulfide passivation of the Al(2)O(3)/GaAs structure improved the effect of Fermi level pinning on the electrical characteristics, thereby providing a higher oxide capacitance, smaller frequency dispersion, and reduced surface states, as well as decreased interfacial charge trapping and gate leakage currents. Photoemission analysis indicated that the (NH(4))(2)S-treated GaAs improved the quality of the as-deposited Al(2)O(3) thin film and preserved the stoichiometry of the dielectric during subsequent high-temperature annealing. This behavior was closely correlated to the diminution of GaAs native oxides and elemental arsenic defects and their unwanted diffusion. In addition, thermal processing under an O(2) atmosphere, relative to that under N(2), decreased the thickness of the Al(2)O(3) gate dielectric and relieved the gate leakage degradation induced by metallic arsenic; as a result, superior dielectric reliability was attained. We discuss the underlying thermochemical reactions that account for these experimental observations. (C) 2008 American Institute of Physics.
Growth of gamma-In2Se3 films on Si substrates by metal-organic chemical vapor deposition with different temperatures
(2008-04-01)
Huang, Yen-Chin
;
Li, Zhen-Yu
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Uen, Wu-Yih
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Lan, Shan-Ming
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Chang, K. J.
In2Se3 films were deposited on the p(+)-Si(1 1 1) substrates by metal-organic chemical vapor deposition (MOCVD) for the first time at temperatures higher than 500 degrees C. Trimethyl indium (TMI) and H2Se were used as the source reactants with the flow ratio of [H2Se]/[TMI] being maintained at 6.7. The growth temperature was varied from 350 to 650 degrees C. Powder X-ray diffraction analyses revealed that the In2Se3 film grown is polycrystalline and has a wurtzite structure when the growth temperature is below 450 degrees C. Instead, a rhombohedral structure began to appear when the growth temperature is above 450 degrees C. Besides, SEM observations indicated a surface morphology of columnar structure for all films grown. Optical properties were examined by photoluminescence (PL) measurements. It was found that by conducting the growth at 550 degrees C a strong PL emission at around 2.14 eV was observed at 20 K. The luminescence mechanism was found to be dominated by the free excitons based on the temperature-dependent PL spectra from 20 to 120 K. However, bound exciton emissions were also observed or even became the dominant band when the films were grown at temperatures lower than 500 degrees C. Otherwise, the intensity of the 2.14 eV peak reduced greatly when the growth temperature was higher than 5 50 degrees C. Power-dependent PL measurements with excitation power varying from 0.1 to 100 mW confirm the luminescent mechanism and the material quality of the film grown at 550 degrees C. It is concluded that single-phase gamma-In2Se3 films can be achieved at temperatures lower than 450 degrees C; however, good-quality In2Se3 films with the simultaneous appearance of gamma- and beta-phase structures can be grown at around 550 degrees C. (C) 2007 Elsevier B.V. All rights reserved.
網站購買意願影響因素之探討
(2008-04-01)
林娟娟
;
陳岱昀
;
Judy Chuan-Chuan Lin
;
Tai-Yun Chen
;
Institute of Business and Management
網際網路的普及與行動通訊技術的快速發展，讓消費者隨時隨地皆能透過網路進行購物或瀏覽資訊，而由於網站爲網路消費者與商家接觸的重要介面，因此網站的資訊系統品質、內容及呈現方式，將影響消費者對網站的使用態度。爲留住顧客並提升其對於網站商品的購買意願，掌握網路消費者之喜好及信任態度，是網站經營者所應致力的目標。本研究彙整電子商務之相關文獻，提出以技術面、社會面及個人面三個層面，探討影響消費者網路購物行爲的前置因子，並提出一適用於網路購物之模型，以協助網站經營者掌握其中之關鍵，增加消費者對購物網站商品的購買意願。本研究使用LISREL統計軟體進行驗證性因素分析，以及結構方程模式分析，實證研究的結果顯示，消費者對網站的喜好及信任態度，正向影響消費者的購買意願，而在影響消費意願之前置因素中，又以消費者對網站的系統品質認知爲購買意願的重要影響因素，而消費者與網站互動產生的愉悅感受及網站的熟悉程度等因素亦顯著影響消費者的網站購物意願。此研究結果除了顯示影響消費者對購物網站商品之購買因素外，亦可瞭解消費者對網站之技術面、社會面及個人層面之認知，對於日後網站經營者在建置網站上，提供參考之依據。
Rapid and homogeneous dispersion of pt catalyst particles on multi-walled carbon nanotubes by temperature-controlled microwave polyol method
(2008-04-01)
Chen, Chieng-Ming
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Chen, Mi
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Yu, Hung-Wei
;
Lu, Su-Chen
;
Chen, Chia-Fu
Fuel cells, particularly direct methanol fuel cells (DMFCs), have great potential as mobile power sources. It has been extensively reported that the DMFC performance strongly depends on the electrode catalyst, and many research groups have focused on the preparation of high efficiency cathode catalysts using all types of metal nanoparticle and support. However, most of these methods are either time-consuming with multiple-steps or there is low loading of the nanocatalyst dispersed on the supports. In this study, platinum nanoparticles of uniform diameter (approximately 4.3 nm) were efficiently dispersed on multi-walled carbon nanotubes (MWCNTs) by the temperature-control led, microwave-assisted polyol method with the addition of sodium dodecyl sulfate (SDS) and [poly(vinyl pyrrolidone)] (PVP). The addition of SDS and PVP in chloroplatinic acid/ethylene glycol (EG) solution can cause the efficient and homogeneous dispersion of the catalyst particles on MWCNTs, enhance the adsorption of platinum particles, and reduce the residue of platinum particles. Moreover, temperature was determined to be the most important factor affecting the reduction of Pt in the process, and large amounts of Pt particles were characterized when the temperature ranged from 140 to 160 degrees C. The results indicate that the optimum temperature ranges from 140 to 160 degrees C, and that the loading amount of Pt/CNTs can reach more than 50 wt % in only 90 s of processing time. The significant improvements in dispersion and loading are due to the ability of SDS, to wrap the PVP-stabilized Pt nanoparticles around the surface of the carbon nanotubes. The characterization analyses were conducted by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and thermal gravinnetric analysis (TGA).
智慧型音訊處理器及其方法
(2008-04-01)
白明憲
;
陳孟君
一種智慧型音訊處理器,包括:一特徵擷取單元接收一音訊訊號,並使用數個音訊描述子對音訊訊號擷取數個特徵値;一資料預處理單元對數個特徵値正規化,以作為智慧型音訊處理系統之分類資訊;以及一分類演算單元依分類資訊將音訊訊號分類成數種不同種類的音樂。
Adaptive two-stage GSC-based PIC detection for time-varying MIMO channels
(2008-04-01)
Lee, Yinman
;
Wu, Wen-Rong
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電信工程研究所
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Institute of Communications Engineering
Adaptive parallel interference cancellation (PIC) has been recently proposed for the signal detection in multiple-input multiple-output (MIMO) systems. However, it suffers from error propagation when operated in time-varying channels. In this letter, an adaptive two-stage PIC with the minimum variance (MV) criterion is proposed to solve the problem. Adaptation with the MV criterion is realized with a decision feedback generalized sidelobe canceller (DFGSC). In the first-stage cancellation, a special structure involving dual DFGSCs is developed. All adaptation operations are implemented with the least-mean-square (LMS) algorithm. Simulations show that the proposed adaptive PIC detection can significantly outperform the conventional adaptive PIC detection in time-varying MIMO channel environments.
Bio-imaging of alpha-bungarotoxin binding to target cell by carboxylated nanodiamond
(2008-04-01)
Chao, Jui-I
;
Liu, Kuang-Kai
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Chen, Mei-Fang
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Chen, Po-Yi
;
Lee, Tony J. F.
Mixing flow characteristics in a vessel agitated by the screw impeller with a draught tube
(2008-04-01)
Tsui, Yeng-Yung
;
Hu, Yu-Chang
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機械工程學系
;
Department of Mechanical Engineering
The circulating flow in a vessel induced by rotating impellers has drawn a lot of interests in industries for mixing different fluids. It used to rely on experiments to correlate the performance with system parameters because of the theoretical difficulty to analyze such a complex flow. The recent development of computational methods makes it possible to obtain the entire flow field via solving the Navier-Stokes equations. In this study, a computational procedure, based on multiple frames of reference and unstructured grid methodology, was used to investigate the flow in a vessel stirred by a screw impeller rotating in a draught tube. The performance of the mixer was characterized by circulation number, power number, and nondimensionalized mixing energy. The effects on these dimensionless parameters were examined by varying the settings of tank diameter, shaft diameter, screw pitch, and the clearance between the impeller and the draught tube. Also investigated was the flow system without the draught tube. The flow mechanisms to cause these effects were delineated in detail.
Dam overtopping risk assessment considering inspection program
(2008-04-01)
Kuo, Jan-Tai
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Hsu, Yung-Chia
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Tung, Yeou-Koung
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Yeh, Keh-Chia
;
Wu, Jian-De
Safety inspection of large dams in Taiwan is conducted every 5 years. The practice does not take into consideration uncertainty of dam conditions. The goal of this study is to determine the optimal dam inspection interval under the consideration of overtopping risk incorporating uncertainty gate availability. In earlier studies, assessment of overtopping risk only considered the uncertainties in reservoir properties and natural randomness of hydrologic events without giving much thought to the availability of spillway gates. As a result, the overtopping risk could be underestimated. In this study, an innovative concept is proposed to evaluate dam overtopping by taking into account spillway gate availability. The framework consists of three parts: (1) evaluation of conditional overtopping risk for different numbers of malfunctioning spillway gates; (2) evaluation of spillway gate availability; and (3) dam inspection scheduling. Furthermore, considerations are given to overtopping risk, inspection cost, and dam break cost for determining the optimal inspection schedule. The methodology is applied to the Shihmen Reservoir in Taiwan and to evaluate its time-dependent overtopping risk. Results show that overtopping risk considering the availability of the spillway gates is higher than the one without considering the availability of the spillway gates.
Multimode G(m)-C channel selection filter for mobile applications in 1-V supply voltage
(2008-04-01)
Lo, Tien-Yu
;
Hung, Chung-Chih
;
電信工程研究所
;
Institute of Communications Engineering
A CMOS transconductor for multimode channel selection filter is presented. The transconductor includes a voltage-to-current converter and a current multiplier. Voltage-to-current conversion employs linear region MOS transistors, and the conversion features high linearity over a wide input swing range. The current multiplier which operates in the weak inversion region provides a wide transconductance tuning range without degrading the linearity. A third-order Butter-worth low-pass filter implemented. with the transconductors was designed by TSMC 0.18-mu m CMOS process. The measurement results show that the filter can operate with the cutoff frequency of 135 kHz to 2.2 MHz. The tuning range and the linearity performance would be suitable for the wireless specifications of GSM, Bluetooth, cdma2000, and wide-band CDMA. In the design, the maximum power consumption at the highest cutoff frequency is 2 mW under a 1-V supply voltage.
RF and logic performance improvement of In0.7Ga0.3As/InAs/In0.7Ga0.3As composite-channel HEMT using gate-sinking technology
(2008-04-01)
Kuo, Chien-I
;
Hsu, Heng-Tung
;
Chang, Edward Yi
;
Chang, Chia-Yuan
;
Miyamoto, Yasuyuki
Eighty-nanometer-gate In0.7Ga0.3As/InAs/ In0.7Ga0.3As composite-channel high-electron mobility transistors (HEMTs), which are fabricated using platinum buried gate as the Schottky contact metal, were evaluated for RF and logic application. After gate sinking at 250 degrees C for 3 min, the device exhibited a high g(m) value of 1590 mS/mm at V-d = 0.5 V, the current-gain cutoff frequency f(T) was increased from 390 to 494 GHz, and the gate-delay time was decreased from 0.83 to 0.78 ps at supply voltage of 0.6 V. This is the highest f(T) achieved for 80-nm-gate-length HEMT devices. These superior performances are attributed to the reduction of distance between gate and channel and the reduction of parasitic gate capacitances during the gate-sinking process. Moreover, such superior performances were achieved through a very simple and straightforward fabrication process with optimal epistructure of the device.