Browsing by Issue Date, starting with "2007-04-23"

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Self-organized tantalum oxide nanopyramidal arrays for antireflective structure
(2007-04-23)
Wu, Chia-Tien
;
Ko, Fu-Hsiang
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Lin, Chun-Hung
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材料科學與工程學系
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材料科學與工程學系奈米科技碩博班
A self-organized tantalum oxide nanopyramidal structure without tedious semiconductor processing is proposed in this letter. Construction of pyramid arrays with a close-packed periodicity of 200 nm and a height of 200 nm was achieved by the anodic alumina template method directly on the substrate. The tantalum oxide nanopyramidal structure was formed as the underlying tantalum film oxidized and localized precisely by the pore of alumina. The reflectance from the spectroscopic measurement suggests that the nanopyramidal array structures have more broadband antireflection (< 2%) than the nanodot arrays and thin film structures. (c) 2007 American Institute of Physics.
Ce3+/Eu2+ codoped Ba2ZnS3: A blue radiation-converting phosphor for white light-emitting diodes
(2007-04-23)
Yang, Woan-Jen
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Chen, Teng-Ming
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應用化學系
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Department of Applied Chemistry
The Ce3+/Eu2+ codoped Ba2ZnS3 phosphor shows intense blue absorption and tunable green-to-red emission. The energy transfer from Ce3+ to Eu2+ in this phosphor has been demonstrated to be a resonant type via an electric dipole-dipole mechanism. The Ba2ZnS3:Ce3+,Eu2+ phosphor would be the great potential application as a blue radiation-converting phosphor for white light-emitting diodes. (c) 2007 American Institute of Physics.
A theoretical study of surface reduction mechanisms of CeO2 (111) and (110) by H-2
(2007-04-23)
Chen, Hsin-Tsung
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Choi, Yong Man
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Liu, Meilin
;
Lin, M. C.
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應用化學系分子科學碩博班
Reaction mechanisms for the interactions between CeO2(111) and (110) surfaces are investigated using periodic density functional theory (DFT) calculations. Both standard DFT and DFT+U calculations to examine the effect of the localization of Ce4f states on the redox chemistry of H-2-CeO2 interactions are described. For mechanistic studies, molecular and dissociative local minima are initially located by placing an H-2 molecule at various active sites of the CeO2 surfaces. The binding energies of physisorbed species optimized using the DFT and DFT+U methods are very weak. The dissociative adsorption reactions producing hydroxylated surfaces are all exothermic; exothermicities at the DFT level range from 4.1 kcalmol(-1) for the (111) to 26.5 kcalmol(-1) for the (110) surface, while those at the DFT+U level are between 65.0 kcalmol(-1) for the (111) and 81.8kcalmol(-1) for the (110) surface. Predicted vibrational frequencies of adsorbed OH and H2O species on the surfaces are in line with available experimental and theoretical results. Potential energy profiles are constructed by connecting molecularly adsorbed and dissociatively adsorbed intermediates on each CeO2 surface with tight transition states using the nudged elastic band (NEB) method. It is found that the U correction method plays a significant role in energetics, especially for the intermediates of the exit channels and products that are partially reduced. The surface reduction reaction on CeO2(110) is energetically much more favorable. Accordingly, oxygen vacancies are more easily formed on the (110) surface than on the (111) surface.
Effect of lath microstructure on the mechanical properties of flow-formed C-250 maraging steels
(2007-04-25)
Lee, Yen-Jung
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Kung, Ming-Chueh
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Lee, I-Kang
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Chou, Chang-Pin
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機械工程學系
A solution treated C-250 maraging steel tubing pre-form was cold forward flow-formed into a seamless tube to attain a 79% wall thickness reduction. Various heat treatments were then conducted on the tube to strengthen the material. This study found that although direct aging treatment could generate the tensile strength exceeded the specification's requirement in all the heat treatment attempts, the C-250 steel suffered loss of ductility in percentage elongation. Through "solution + aging" treatment, the steel's ductility was much improved and tensile properties can still meet the specification. The pre-treatment of high homogenization temperature could produce coarse lath martensitic microstructure and result in a decrease of the tensile strength of the C-250 steel. Furthermore, the C-250 steel also showed the presence of seemingly globular precipitates within the lath structure. Detailed discussion of mechanical properties obtained for each of the heat-treated steels in terms of microstructures and metallographic works was presented. (c) 2006 Elsevier B.V. All rights reserved.
Context-aware frame memory scheme for motion compensation in video decoding
(2007-04-26)
Chang, Nelson Yen-Chung
;
Chang, Tian-Sheuan
The present invention provides a context-aware frame memory scheme for motion compensation in video decoding, which utilizes a motion compensator to receive a data block from input video decoding, follow by processing both inputted context characteristic of residual block and motion vector respectively. The conception of technology is first based on the context characteristic of input video data decoding block, if there is no residual value and motion vector, it will be defined as “perfect match block”; otherwise, “non-perfect match block” instead. Then, the circuit architecture for memory accessing in video decoding provided by present invention will perform different memory access steps for the above mentioned two types of block. If one determines that a block is “non-perfect match block”, selectively choose the reference frame as a back-up data; On contrary, if a block is “perfect match block”, it represents there is no difference between both reference frame and reconstructive frame, hence no access is required to the main frame memory, which means that the access frequency can be minimized; therefore, it can minimize the consumption of the memory capacity as well.
Novel vertical handover control algorithm for WLAN and UMTS
(2007-04-26)
Huang, Ching Yao
;
Chou, Chie Ming
In this invention, a novel vertical handover control algorithm, consisting of a throughput-based mapping function, QoS-based dynamic handover thresholds, and performance-based trigger timers, are proposed to resolve uncommon pilot problem, QoS requirements, and ping-pong effects, respectively. An analytic model based on a finite state machine is developed to evaluate the proposed algorithm in terms of the handover frequency and achievable throughput. A numerical analysis is also provided to further quantify the performance impacts.
Computer executable graphic method of generating animation elements
(2007-04-26)
Chen, Ming-Jang
A computer executable graphic method of generating animation elements realized with computer software is provided, which is capable of being plugged in a computer graphics application, recorded in a recording and storage medium, or executed on a computer executable platform. Through an operating mode of a graphic user interface provided by a graphics system, various objects can be established to form various animation elements, and the animation elements can be activated with a trigger event executed by an input device to generate various interactive animation effects. According to the present method, a user can operate in a graphic mode to establish and generate an interactive animation visually, simply, and rapidly.
Low refractive index Si nanopillars on Si substrate
(2007-04-30)
Lin, Gong-Ru
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Chang, Ya-Chung
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Liu, En-Shao
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Kuo, Hao-Chung
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Lin, Huang-Shen
Low refractive index of a stalagmitelike high-aspect-ratio Si nanopillar array on Si dry etched using a self-aggregated Ni nanodot mask is demonstrated, which exhibits two minimum reflectances of 1.23 and 1.4 with corresponding refractive indices of 1.25 and 1.48 at 400 and 1200 nm, respectively. Angular dependency of the transverse electrical mode reflectance at 632.8 nm of the surface roughened Si nanopillar array is released, and the Brewster angle of 63 degrees with equivalent refractive index of 1.5 is determined. (C) 2007 American Institute of Physics.
Nonvolatile low-temperature polycrystalline silicon thin-film-transistor memory devices with oxide-nitride-oxide stacks
(2007-04-30)
Liu, Po-Tsun
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Huang, C. S.
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Chen, C. W.
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光電工程學系
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顯示科技研究所
Nonvolatile memory devices with oxide-nitride-oxide stack structures were fabricated on glass substrates using low-temperature polycrystalline silicon technology. The Fowler-Nordheim tunneling scheme is more suitable than channel hot carrier injection for the programming of the polycrystalline silicon nonvolatile memory device. A memory window of 1.5 V can be obtained at a programming voltage of 20 V. After 10(4) programming/erasing cycles, a threshold voltage shift of 1.5 V is maintained. Furthermore, the proposed memory device exhibits good retention for 50 h at 60 degrees C without a significant decline in the memory window. (C) 2007 American Institute of Physics.
Effects of strained InGaN interlayer on contact resistance between p-GaN and indium tin oxide
(2007-04-30)
Lee, Chi-Ling
;
Lee, Wei-I
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電子物理學系
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Department of Electrophysics
Indium tin oxide (ITO), with its transparency and strong adhesion to GaN, has been used as a replacement for Ni/Au as a contact on p-GaN. However, ITO suffers from high contact resistance on p-GaN. In this work, low contact resistance between ITO and the p-GaN layer was consistently achieved using various strained InGaN layers as the interface layers between ITO and p-GaN layer. The doping of InGaN, whether n type or p type, has a relatively weak effect on the contact resistance as long as the thickness of the InGaN layer is adequately controlled. The secondary-ion-mass spectroscopy depth profile reveals that the n-type InGaN strained contact layer was also heavily doped with Mg. Results of this study demonstrate that the piezoelectric field between InGaN and p-GaN is important in reducing the barrier height of Ohmic contact. (c) 2007 American Institute of Physics.
Quantitative phase retrieval in transmission hard x-ray microscope
(2007-04-30)
Yin, Gung-Chian
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Chen, Fu-Rong
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Hwu, Yeukuang
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Shieh, Han-Ping D.
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Liang, Keng S.
Quantitative phase retrieval with a sub-100-nm resolution is achieved from micrographs of a zone plate based transmission x-ray microscope. A plastic zone plate containing objects of sizes from micrometers down to tens of nanometers is used as a test sample to quantify the retrieved phase. Utilizing the focal serial images in the image plane, the phase information is retrieved quantitatively across the entire range of sizes by combining the transport intensity equation and self-consistent wave propagation methods in this partial coherence system. The study demonstrates a solution to overcome the deficiency encountered in the two phase retrieval approaches. (c) 2007 American Institute of Physics.
Optical characteristics of a-plane InGaN/GaN multiple quantum wells with different well widths
(2007-04-30)
Ko, T. S.
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Lu, T. C.
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Wang, T. C.
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Lo, M. H.
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Chen, J. R.
a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm were grown on r-plane sapphire by metal organic chemical vapor deposition for investigation. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL study shows that the sample with 3-nm-thick wells has a better optical property with a fast exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify the more uniform and stronger luminescence intensity distribution observed for the samples of thinner quantum wells, indicating that the important growth parameters for a-plane InGaN/GaN multiple quantum wells could be dominated by the In fluctuation and crystal quality during the epitaxial growth. (c) 2007 American Institute of Physics.
A non-additive model for evaluating airline service quality
(2007-05-01)
Liou, James J. H.
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Tzeng, Gwo-Hshiung
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科技管理研究所
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Institute of Management of Technology
This study develops a non-additive model for evaluating and improving the service quality of airlines and compares its results with the conventional additive method. Service quality is a composite of various attributes and many in a system have inter-dependent characteristics that may not be correctly evaluated using conventional additive measures. A fuzzy integral is thus proposed. Factor analysis is initially used to extract some independent common-factors and fuzzy integral used to integrate the performance ratings of inter-dependent attributes in each common-factor. For the analytic hierarchy process a pair-wise comparative approach is adopted to determine the relative weights linking each independent common-factor. Finally, Grey relation analysis and simple additive weight method are used to find airline service quality. A study of international airlines is conducted for verification. Safety and reliability emerge as the critical factors of service quality. (C) 2007 Elsevier Ltd. All rights reserved.
Patterned self-assembly of magnetic biomolecules on semiconductor substrates
(2007-05-01)
Sun, Kien Wen
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Chang, Chia-Ching
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生物科技學系
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應用化學系
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應用化學系分子科學碩博班
The paper reports on the methods of preparing and patterning magnetic metallothionein (Mn,Cd-MT-2) molecules on semiconductor surfaces. The molecules are placed into nanopores prepared on silicon (0 0 1) substrates. We observe the self-assembled growth of those MT molecules on the patterned Si surface. Dense arrays of molecular rods are demonstrated on templates with small pores and pitch sizes. Then the structures of the self-assembled protein are studied by atomic force microscopy (AFM) and magnetic force microscopy (MFM). Our measurements indicate that molecular self-assembly has a magnetic dipole moment which interacts with the applied magnetic field. (c) 2007 Elsevier Ltd. All rights reserved.
Evaluating intertwined effects in e-learning programs: A novel hybrid MCDM model based on factor analysis and DEMATEL
(2007-05-01)
Gwo-Hshiung Tzeng
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Cheng-Hsin Chiang
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Chung-Wei Li
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科技管理研究所
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Institute of Management of Technology
Internet evolution has affected all industrial and commercial activity and accelerated e-learning growth. Due to cost, time, or flexibility for designer courses and learners, e-learning has been adopted by corporations as an alternative training method. E-learning effectiveness evaluation is vital, and evaluation criteria are diverse. A large effort has been made regarding e-learning effectiveness evaluation; however, a generalized quantitative evaluation model, which considers both the interaffected relation between criteria and the fuzziness of subjective perception concurrently, is lacking. In this paper, the proposed new novel hybrid MCDM model addresses the independent relations of evaluation criteria with the aid of factor analysis and the dependent relations of evaluation criteria with the aid of DEM-ATEL. The AHP and the fuzzy integral methods are used for synthetic utility in accordance with subjective perception environment. Empirical experimental results show the proposed model is capable of producing effective evaluation of e-learning programs with adequate criteria that tit with respondent's perception patterns, especially when the evaluation criteria are numerous and intertwined. (C) 2006 Elsevier Ltd. All rights reserved.
10-GHz highly symmetrical sub-harmonic Gilbert mixer using GaInP/GaAs HBT technology
(2007-05-01)
Wu, Tzung-Han
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Meng, Chinchun
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電信工程研究所
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Institute of Communications Engineering
A 10-GHz sub-harmonic Gilbert mixer is demonstrated using GaInP/GaAs hetero-junction bipolar transistor technology. The local oscillator (LO) signal time-delay path in the sub-harmonic LO stage is compensated using the fully symmetrical stacked-LO doubler; therefore, the balance of the sub-harmonic LO stage, the radio frequency to intermediate frequency isolation, and IIP2 are improved. The demonstrated 10-GHz sub-harmonic mixer achieves 10 dB conversion gain, IP1dB of -12 dBm, IIP3 of 2 dBm and IIP2 of 33 dBm.
Optical characterization of Zn0.97Mn0.03Se/ZnSe0.92Te0.08 type II multiple-quantum-well structures
(2007-05-01)
Lin, D. Y.
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Shiu, J. J.
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Wu, J. D.
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Yang, C. S.
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Chou, W. C.
The optical characterization of type II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures have been studied using photoluminescence (PL), temperature-dependent PL, polarized PL, power-dependent PL, and photoreflectance (PR) in this study. The PL data reveal that the band alignment of the ZnMnSe/ZnSeTe system is type II. Comparing with the theoretical calculation based on the Schrodinger equation, the valence band offset is estimated to be 0.6 eV. From the power-dependent PL spectra, it is observed that the peak position of PL spectra shows a blueshift under different excitation power. The blueshift can be interpreted in terms of the band-bending effect due to spatially photoexcited carriers in a type II alignment. The thermal activation energy (E-A) for quenching the PL intensity was determined from temperature-dependent PL spectra. The thermal activation energy was found to decrease as the thickness of ZnMnSe and ZnSeTe layers decreased. The polarized PL spectra exhibit a large in-plane polarization with the polarization degree up to 50%. The polarization does not depend on the excitation intensity as well as temperature. The large polarization is an inherent orientation of the interface chemical bonds. The higher transition features observed in PR spectra show a blueshift with the similar trend observed in the PL spectra as decreasing the thickness of ZnSeTe layer. This result provides a consistent evidence for the assumption that square-like well shapes were built in the ZnSeTe layers. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Properties of vortex propagation in a niobium film with spacing-graded density of pinning sites
(2007-05-01)
Horng, Lance
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Wu, T. C.
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Wu, J. C.
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Cao, R.
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Yang, T. J.
The vortex propagation has been investigated in Nb superconductors with one dimension spacing-graded density of submicrometer-scaled holes in this research. A rectification effect can be discerned because the applied ac is transformed into a net dc voltage. These results demonstrate that the rectification is mainly characterized by the asymmetric pinning landscape and the rectified voltage depends considerably on temperature and the amplitude of applied ac. The dc voltage increases steeply up to the maximum value and then decreases to zero dc voltage with the increase of ac. The shape of peaks in the dc voltage signal become steeper and move to higher applied ac regime with the decrease of temperature.
Nonplanar modeling and experimental validation of a spindle-disk system equipped with an automatic balancer system in optical disk drives
(2007-05-01)
Chao, Paul C. -P.
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Sung, Cheng-Kuo
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Wu, Szu-Tuo
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Huang, Jeng-Sheng
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電控工程研究所
Non-planar dynamic modeling and experimental validation of a spindle-disk system equipped with an automatic ball-type balancer system (ABS) in optical disc drives are performed in this study. Recent studies about planar dynamic modeling and analysis have shown the capability of the ABS in spindle-disk assembly via counteracting the inherent imbalance. To extend the analysis to be practical, non-planar dynamic modeling are conducted in this study to re-affirm the pre-claimed capability of the ABS system, along with experiments being designed and conducted to validate the theoretical findings. Euler angles are first utilized to formulate potential and kinetic energies, which is followed by the application of Lagrange's equation to derive governing equations of motion. Numerical simulations are next carried out to explore dynamic characteristics of the system. It is found that the levels of residual runout (radial vibration), as compared to those without the ABS, are significantly reduced, while the tilting angle of the rotating assembly can be kept small with the ABS installed below the inherent imbalance of the spindle-disk system. Experimental study is also conducted, and successfully validates the aforementioned theoretical findings. It is suggested that the users of the ABS need to cautiously operate the spindle motor out of the speeds close to the resonances associated with various degrees of freedom. In this way, the ABS could hold the expected capability of reducing vibration in all important directions, most importantly in radial directions.
Sub-THz photonic-transmitters based on separated-transport-recombination photodiodes and a micromachined slot antenna
(2007-05-01)
Li, Yu-Tai
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Shi, J.-W.
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Pan, Ci-Ling
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Chiu, C.-H.
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Liu, W.-S.
We demonstrate a novel photonic transmitter, which is composed of a low-temperature-grown GaAs (LTG-GaAs)-based separated-transport-recombination photodiode and a micromachined slot antenna. Under femtosecond optical pulse illumination, this device radiates strong electrical pulses (4.5-mW peak power) without the use of a Si-lens. It can be observed in the Fourier transform infrared spectrometer spectrum of radiated pulses that a significant resonance, with a peak power of approximately 300 mu W, occurs at 500 GHz, which corresponds to the designed resonant frequency of the slot antenna. The saturation problem related to the output terahertz power that occurs with the traditional LTG-GaAs-based photonic-transmitters when operated under high external applied electrical fields (> 50 kV/cm) has been eliminated by the use of our device.