Browsing by Issue Date, starting with "2007-11-05"

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Highly efficient non-doped blue-light-emitting diodes based on an anthrancene derivative end-capped with tetraphenylethylene groups
(2007-11-05)
Shih, Ping-I
;
Chuang, Chu-Ying
;
Chien, Chen-Han
;
Diau, Eric Wei-Guang
;
Shu, Ching-Fong
A novel blue-emitting material, 2-tert-butyl-9,10-bis[4-(1,2,2-triphenylvinyl)phenyl]anthracene (TPVAn), which contains an anthracene core and two tetraphenylethylene end-capped groups, has been synthesized and characterized. Owing to the presence of its sterically congested terminal groups, TPVAn possesses a high glass transition temperature (155 degrees C) and is morphologically stable. Organic light-emitting diodes (OLEDs) utilizing TPVAn as the emitter exhibit bright saturated-blue emissions (Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of x = 0.14 and y = 0.12) with efficiencies as high as 5.3% (5.3 cd A(-1)) - the best performance of non-doped deep blue-emitting OLEDs reported to date. In addition, TPVAn doped with an orange fluorophore served as an authentic host for the construction of a white-light-emitting device that displayed promising electroluminescent characteristics: the maximum external quantum efficiency reached 4.9% (13.1 cd A(-1)) with CIE coordinates located at (0.33, 0.39).
Microwave annealing of polymer photovoltaic devices
(2007-11-05)
Ko, Chu-Jung
;
Lin, Yi-Kai
;
Chen, Fang-Chung
;
光電工程學系
;
Department of Photonics
A selective microwave irradiation annealing method for the preparation of efficient polymer photovoltaic devices is reported. The power conversion efficiency of the devices increases upon increasing the irradiation time. In situ temperature probing suggests that the microwaves could penetrate the anode without any loss of energy, whereas the organic active layer and the cathode were both heated. Furthermore, X-ray diffraction indicated that microwave annealing enhanced the degree of crystallization of the polymer chains.
Efficient deep-blue organic light-emitting diodes: Arylamine-substituted oligofluorenes
(2007-11-05)
Gao, Zhi Qiang
;
Li, Zhong Hui
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Xia, Ping Fan
;
Wong, Man Shing
;
Cheah, Kok Wai
Novel deep-blue-light-emitting diphenylamino and triphenylamino end-capped oligofluorenes were synthesized by double palladium-catalyzed Suzuki cross- coupling of dibromo-oligofluorene with the corresponding boronic acid as a key step. These oligofluorenes exhibit deep-blue emission (lambda(em)(max) = 429-432 nm), low and reversible electrochemical oxidation (highest occupied molecular orbital = 5.15-5.20 eV), high fluorescence quantum yield (Phi(FL) = 0.61-0.93), and good thermal properties (glass-transition temperature, T-g = 99-195 degrees C and decomposition temperature, T-dec > 450 degrees C). Remarkably, saturated deep-blue organic light-emitting diodes, made from these oligofluorenes as dopant emitters, have been achieved with excellent performance and maximum efficiencies up to 2.9 cd A(-1) at 2 mA cm(-2) (external quantum efficiency of 4.1 %) and with Commission Internationale de l'Eclairage (x,y) coordinates of (0.152,0.08), which is very close to the National Television System Committee standard blue.
Dispersion of nanoscale BaTiO3 suspensions by a combination of chemical and mechanical grinding/mixing processes
(2007-11-05)
Ying, Kuo-Liang
;
Hsieh, Tsung-Eong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The colloidal stability of aqueous nanometer- and micrometer-scale barium titanate (BaTiO3) utilizing poly (methacrylic acid) (PMAA-Na) and polyacrylamide/(alpha-N,N-dimethyl-N-acryloyloxyethyl)ammonium ethanate (PDAAE) was investigated. In addition to chemical dispersants, the effects of mechanical milling using either conventional ball milling or nanogrinding/-mixing on the dispersion of BaTiO3 suspensions were also studied. Characterization of the particle size distribution (d(50)), viscosity, and morphology of BaTiO3 particles in the suspensions revealed that a sole chemical dispersant or mechanical milling was insufficient to achieve nanometer-scale dispersion. The best dispersion results were obtained with a combination of PMAA-Na dispersant and nanogrinding/-mixing, which could provide sufficient electronic repulsive force and shear force to disperse the 80-nm BaTiO3 powders uniformly in the aqueous suspension. (C) 2007 Wiley Periodicals, Inc.
Nonvolatile Si/SiO2/SiN/SiO2/Si type polycrystalline silicon thin-film-transistor memory with nanowire channels for improvement of erasing characteristics
(2007-11-05)
Chen, Shih-Ching
;
Chang, Ting-Chang
;
Liu, Po-Tsun
;
Wu, Yung-Chun
;
Chin, Jing-Yi
A silicon-oxide-nitride-oxide-silicon type polycrystalline silicon thin-film transistor (poly-Si TFT) with nanowire channels was investigated for both transistor and memory applications. The poly-Si TFT memory device has superior electrical characteristics, such as higher drain current, smaller threshold voltage, and steeper subthreshold slope. Also, the simulation result on electrical field reveals that the electrical field across the tunnel oxide is enhanced and that across the blocking oxide is reduced at the corner regions. This will lead to the parasitic gate injection activity and the erasing speed can be apparently improved in the memory device due to the pronounced corner effect and narrow channel width.
Soluble phenanthrenyl-imidazole-presenting regioregular poly (3-octylthiophene) copolymers having tunable bandgaps for solar cell applications
(2007-11-05)
Chang, Yao-Te
;
Hsu, So-Lin
;
Su, Ming-Hsin
;
Wei, Kung-Hwa
;
材料科學與工程學系
We have used Grignard metathesis polymerization to successfully synthesize a series of regioregular polythiophene copolymers that contain electron-withdrawing and conjugated phenanthrenyl-imidazole moieties as side chains. The introduction of the phenanthrenyl-imidazole moieties onto the side chains of the regioregular polythiophenes increased their conjugation lengths and thermal stabilities and altered their bandgap structures. The bandgap energies, determined from the onset of optical absorption, could be tuned from 1.89 eV to 1.77 eV by controlling the number of phenanthrenyl-imidazole moieties in the copolymers. Moreover, the observed quenching in the photoluminescence of these copolymers increases with the number of phenanthrenyl-imidazole moieties in the copolymers, owing to the fast deactivation of the excited state by the electron-transfer reaction. Both the lowered bandgap and fast charge transfer contribute to the much higher external quantum efficiency of the poly (3-octylthiophene)-side-chain-tethered phenanthrenyl-imidazole than that of pure poly(3-octylthiophene), leading to much higher short circuit current density. In particular, the short circuit current densities of the device containing the copolymer having 80 mol % phenanthrenyl-imidazole, P82, improved to 14.2 mA cm(-2) from 8.7 mA cm(-2) for the device of pure poly(3-octylthiophene), P00, an increase of 62 %. In addition, the maximum power conversion efficiency improves to 2.80 % for P82 from 1.22 % for P00 (pure P30T). Therefore, these results indicate that our polymers are promising polymer photovoltaic materials.
交大e-News第013期
(2007-11-05)
Secretariat
;
國立交通大學秘書室
Fabrication of InGaN/GaN nanorod light-emitting diodes with self-assembled Ni metal islands
(2007-11-07)
Chiu, C. H.
;
Lu, T. C.
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Huang, H. W.
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Lai, C. F.
;
Kao, C. C.
We report the fabrication of InGaN/GaN nanorod light-emitting diodes (LEDs) using inductively coupled plasma reactive-ion etching (ICP-RIE) and a photo-enhanced chemical (PEC) wet oxidation process via self-assembled Ni nanomasks. An enhancement by a factor of six times in photoluminescence (PL) intensities of nanorods made with the PEC process was achieved in comparison to that of the as-grown structure. The peak wavelength observed from PL measurement showed a blue shift of 3.8 nm for the nanorods made without the PEC oxidation process and 8.6 nm for the nanorods made with the PEC oxidation process from that of the as-grown LED sample. In addition, we have demonstrated electrically pumped nanorod LEDs with the electroluminescence spectrum showing more efficiency and a 10.5 nm blue-shifted peak with respect to the as-grown LED sample.
Capacity-based compressed mode control method for inter-system handover in universal mobile telecommunication system
(2007-11-08)
Huang, Ching Yao
;
Chang, Cheng Ta
;
Ho, Chieh Yuan
The Inter-System handover is one of the key features in the third generation cellular systems. The compressed mode, with variable transmission gaps and power levels, is standardized to support the inter-frequency system handover. To minimize the use of system resources while maintaining the border-cell handover quality, a capacity-based compressed mode control method of the present invention is proposed. Considering the tradeoff between the capacity and the communication quality, the control method can adaptively manage the compressed mode operation based on the potential impacts on the capacity and the effectiveness of the compressed mode measurement. The present invention will improve the effectiveness and performance of the compressed mode operation.
Method for parameter identification and parameter optimization of microspeakers
(2007-11-08)
Bai, Mingsian R.
;
Chen, Rong Liang
The present invention discloses a method for parameter identification and parameter optimization of microspeakers. Measurement procedures for identifying electromechanical constants of microspeaker and a GUI are developed to facilitate estimation of electroacoustic parameters of the microspeaker under test. In light of the thus identified microspeaker parameters, a parameter optimization procedure is carried out to obtain the design that attains the best acoustic performance with minimum harmonic distortion.
Dual bandpass filter having serial configuration of coupled-line filters
(2007-11-08)
Chung, Shyh-Jong
;
Lin, Ke-Chiang
;
Chang, Chun-Fu
Two second-order bandpass filter are connected serially to obtain a dual bandpass filter. One is inductive and the other is capacitive. One has a low passband and the other has a high passband. Between them, a finite transmission zero is formed to suppress noise. The present invention achieves a passband as wide as 1 gigahertz so that it can be applied to a wireless local network, communication equipments and electronic devices.
Virtual machine support for zero-loss Internet service recovery and upgrade
(2007-11-10)
Chang, Da-Wei
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Hsieh, Cheng-En
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Chen, Yan-Pai
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Chiu, Kwo-Cheng
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資訊工程學系
Software is critical for Internet service availability since an Internet service may become unavailable due to software faults or software maintenance. In this paper, we propose a framework to allow zeroloss recovery and online maintenance for Internet services. The framework is based on the virtual machine (VM) technology and a connection migration technique called FT-TCP. It can recover transient application/operating system faults and it allows fault recovery and online maintenance on a single host. The framework substantially enhances FT-TCP so that it can be run efficiently in the VM environment. Specifically, we propose techniques to reduce the inter-VM switches and communication. Moreover, we propose service-specific optimizations to reduce the recovery time of FT-TCP. Finally, the framework provides an interface for the service designers to implement more service-specific optimizations. The framework was implemented by modifying an open source VM monitor, Xen, and the Linux kernel running on top of Xen. The effectiveness and efficiency of the framework were evaluated by running two Internet services, WWW proxy and FTP, on the proposed framework and measuring the impact on their performance. According to the experimental results, our approach causes only slight performance overhead (i.e. less than 4%) and memory overhead (i.e. less than 750 KB) for both the services. Copyright (C) 2007 John Wiley & Sons, Ltd.
Polycrystalline silicon thin-film transistors with location-controlled crystal grains fabricated by excimer laser crystallization
(2007-11-12)
Tsai, Chun-Chien
;
Lee, Yao-Jen
;
Chiang, Ko-Yu
;
Wang, Jyh-Liang
;
Lee, I-Che
In this paper, location-controlled silicon crystal grains are fabricated by the excimer laser crystallization method which employs amorphous silicon spacer structure and prepatterned thin films. The amorphous silicon spacer in nanometer-sized width formed using spacer technology is served as seed crystal to artificially control superlateral growth phenomenon during excimer laser irradiation. An array of 1.8-mu m-sized disklike silicon grains is formed, and the n-channel thin-film transistors whose channels located inside the artificially-controlled crystal grains exhibit higher performance of field-effect-mobility reaching 308 cm(2)/V s as compared with the conventional ones. This position-manipulated silicon grains are essential to high-performance and good uniformity devices. (c) 2007 American Institute of Physics.
Water passivation effect on polycrystalline silicon nanowires
(2007-11-12)
Lin, Horng-Chih
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Su, Chun-Jung
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Hsiao, Cheng-Yun
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Yang, Yuh-Shyong
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Huang, Tiao-Yuan
Defects present in the grain boundaries of polycrystalline materials are known to impede carrier transport inside the materials, and the electronic device performance having such materials as active channels will be adversely affected. In this work, dramatic improvement in device performance was observed as field-effect transistors with polycrystalline silicon nanowire (poly-SiNW) channels were exposed to a wet environment. Passivation of defects in the poly-SiNW by H+ and/or OH- contained in the aqueous solution is proposed to explain the phenomenon. (c) 2007 American Institute of Physics.
Direct visualization of triplex DNA molecular dynamics by fluorescence resonance energy transfer and atomic force microscopy measurements
(2007-11-12)
Chang, Chia-Ching
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Lin, Po-Yen
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Chen, Yen-Fu
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Chang, Chia-Seng
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Kan, Lou-Sing
We have detected the dynamics of 17-mer DNA triplex dissociation mechanism at the molecular level. Fluorescence resonance energy transfer (FRET) was used as an indicator of intermolecular interaction in nanometer range, whereas atomic force microscopy (AFM) was employed to address single molecule with sub-angstrom precision. The maximum rupture force of DNA triplex was found at pH 4.65, consistent with macroscopic observations. These results indicated that the FRET together with an AFM detection system could be used to reveal the DNA triplex interaction in nanometer scale unambiguously. (c) 2007 American Institute of Physics.
Linear relations and their breakdown in high energy massive string scatterings in compact spaces
(2007-11-12)
Lee, Jen-Chi
;
Yang, Yi
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電子物理學系
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Department of Electrophysics
We calculate high energy massive scattering amplitudes of closed bosonic string compactified on the torus. For each fixed mass level with given quantized and winding momenta (m/R ,1/2 nR), we obtain infinite R linear relations among high energy scattering amplitudes of different string states. For some kinematic regimes, we discover that linear relations with N-R = N-L break down and, simultaneously, the amplitudes enhance to power-law behavior instead of the usual exponential fall-off behavior at high energies. It is the space-time T-duality symmetry that plays a role here. This result is consistent with the coexistence of the linear relations and the softer exponential fall-off behavior of high energy string scattering amplitudes as we pointed out previously. It is also reminiscent of our previous work on the power-law behavior of high energy string/domain-wall scatterings. (c) 2007 Elsevier B.V. All rights reserved.
Process for manufacturing self-assembled nanoparticles
(2007-11-13)
Chen
;
Wei-Kuo
;
Lee
;
Ming-Chih
;
Chou
Process for fabricating self-assembled nanoparticles on buffer layers without mask making and allowing for any degree of lattice mismatch; that is, binary, ternary or quaternary nanoparticles comprising Groups III-V, II-VI or IV-VI. The process includes a first step of applying a buffer layer, a second step of turning on the purge gas to modulate the first reactant to the lower first flow rate, then the second reactant is supplied to the buffer layer to form a metal-rich island on the buffer layer, and a third step of turning on purge gas again to modulate the first reactant to the higher second flow rate onto the buffer layer. On the metal-rich island is formed the nanoparticles of the binary, ternary or quaternary III-V, II-VI and IV-IV semiconductor material. This is then recrystallized under the first reactant flow at high temperature forming high quality nanoparticles.
Characterizing the Hsincheng active fault in northern Taiwan using airborne LiDAR data: Detailed geomorphic features and their structural implications
(2007-11-15)
Chan, Yu-Chang
;
Chen, Yue-Gau
;
Shih, Tian-Yuan
;
Huang, Chung
;
土木工程學系
We applied newly acquired high-resolution airborne LiDAR data to study a segment of the Hsincheng fault, a well-known active fault near a large industrial park in northern Taiwan. The Hsincheng fault has received much attention and study in the past; but high spatial resolution digital elevation models have not previously been applied to the study of the fault and its surrounding structures. We processed the acquired LiDAR data and produced I in digital elevation models (DEMs) to investigate the active fault adjacent to the densely populated and important infrastructure in Taiwan. Using the LiDAR DEMs, aerial photographs and topographic maps, we show highly detailed geomorphic characteristics around the study area of the Hsincheng fault. Three major characteristics of the study area are defined that include three very well preserved river terraces at varying levels, the fault/fold scarp of the Hsincheng fault, and meandering river systems. Using the LiDAR DEMs, we were able to detect with precision several fault/fold scarps and very gentle NE-trending folding of the river terraces. In general, the LiDAR DEMs have provided unprecedented clarity of landforms for one segment of the Hsincheng fault, which has helped the characterization of subtle but important geomorphic features. (c) 2007 Elsevier Ltd. All rights reserved.
Growth and characteristics of lead sulfide nanocrystals produced by the porous alumina membrane
(2007-11-15)
Chen, Jung-Hsuan
;
Chao, Chuen-Guang
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Ou, Jong-Chyan
;
Liu, Tzeng-Feng
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材料科學與工程學系
Lead sulfide (PbS) nanocrystals were formed by using Pb nanowires reacted with hydrogen sulfide (H2S) gas. The structure and composition of the as-prepared nanocrystals were confirmed by scanning electron microscopy, X-ray diffraction, transmission electron microscope and energy dispersive X-ray spectroscopy. According to the differential scanning calorimeter analysis, the PbS nanocrystals in a cubic structure owned excellent thermal stability. Furthermore, the optical properties including photoluminescence (PL) and Raman scatting spectrum were also measured. The PL emission measurement of the PbS nanocrystal showed that there was an orange-red emission peak located around 655 nm. A significant quantum confinement effect made the energy gap of PbS produce a blue shift from 0.41 eV to 1.9 eV. (C) 2007 Elsevier B.V. All rights reserved.
Anomalous phase behavior and apparent anharmonicity of the pump-probe signal in a two-dimensional harmonic potential system
(2007-11-15)
Taneichi, T.
;
Kobayashi, T.
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先進超快雷射研究中心
;
Adv Ultrafast Laser Ctr
Discussion on wavelength dependent "anharmonic" effects in a pump-probe signal for a system of wavepacket on one- and two-dimensional harmonic potentials was given. The Fourier power spectrum of the signal, calculated for a model composed of a three-state electronic system coupled to a set of displaced harmonic oscillators, depends on the pulse duration. Condition under which the wavepacket motion in the harmonic potential substantially deviates from that of the classical point mass is derived. The Fourier power spectrum has enhanced components with frequencies of harmonies even in a system composed of ideally harmonic potentials. Utility of the Fourier analysis of the spectrum for clarification of the squeezed molecular vibrational state is discussed. Calculated oscillatory behavior in phase of a pump-probe signal, as a function of probe frequency, was discussed in terms of a two-dimensional effect on a pump-probe signal. (C) 2007 Elsevier B.V. All rights reserved.