Browsing by Issue Date, starting with "2007-08-13"

Now showing 1 - 20 of 59265

Highly efficient and stable white light organic light-emitting devices
(2007-08-13)
Lin, Mei-Fang
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Wang, Lei
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Wong, Wai-Kwok
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Cheah, Kok-Wai
;
Tam, Hoi-Lam
A highly efficient two-element white light organic light-emitting device with a sky blue dopant BUBD-1 and a yellow dopant TBRb was fabricated. The device achieved an electroluminescence efficiency of 17.1 cd/A and 7.9 lm/W at 20 mA/cm(2). From 112 to 32 010 nits, the CIEx,y coordinates variation was Delta(x,y)<+/-(0.01,0.01), which is superior to common white light organic light-emitting devices (OLEDs) that tend to change color with drive conditions. Moreover, the device reached a half-decay t(1/2) lifetime over 40 000 h at an initial luminance of 300 cd/m(2). This result is among the best records of fluorescent white light OLEDs. (C) 2007 American Institute of Physics.
Liquid crystal surface alignments by using ion beam sputtered magnetic thin films
(2007-08-13)
Wu, Hsin-Ying
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Pan, Ru-Pin
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電子物理學系
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Department of Electrophysics
A method for liquid crystal surface alignment by using a one-step, ion beam bombardment of the glass substrates is demonstrated. Precoating by polyimide is not necessary. The authors show that the homeotropic alignment is achieved due to orientation of the diamagnetic nematogenic molecules by the magnetic field from the gamma-Fe2O3 ferrimagnetic thin films created on the substrates by ion beam bombardment. The film exhibits a high Curie temperature well above 300 K and a compensation temperature which is the typical feature of ferrimagnetism. This is a simple, noncontact, and reliable alignment method for liquid crystal devices. (C) 2007 American Institute of Physics.
Investigation of the transient symmetric H state in a pi cell
(2007-08-13)
Yang, Bo-Ru
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Elston, Steve J.
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Raynes, Peter
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Shieh, Han-Ping D.
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光電工程學系
The so-called symmetric H (H-s) state has been reported to have submillisecond response times, which results from the symmetric profile of the liquid crystal director; however, no direct evidence has been obtained to show the profile symmetry. The difficulty in proving this symmetric structure by direct observation results from the short lifetime of H-s state (typically around a few tens of milliseconds). In the work reported here, the authors utilize a burst driving method along with stroboscopic illumination from blue and red light emitting diodes to capture conoscopic images for the H-s director profile; these showed good agreement with their modeling. (c) 2007 American Institute of Physics.
Transparent photo-curable co-polyacrylate/silica nanocomposites prepared by sol-gel process
(2007-08-15)
Chou, Yen-Chun
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Wang, Yu-Young
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Hsieh, T.-E.
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材料科學與工程學系
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Department of Materials Science and Engineering
This work prepared the highly transparent photo-curable co-polyacrylate /silica nanocomposites by using sol-gel process. The FTIR and C-13 NMR analyses indicated that during the sol-gel process, the hybrid precursors transform into composites containing nanometer-scale silica particles and crosslinked esters/ anhydrides. Transmission electron microscopy (TEM) revealed that the silica particles within the average size of 11.5 nm uniformly distributed in the nanocomposite specimen containing about 10 wt% of Si. The nanocomposite specimens exhibited satisfactory thermal stability that they had 5% weight loss decomposition temperatures higher than 150 degrees C and coefficient of thermal expansion (CTE) less than 35 ppm/degrees C. Analysis via derivative thermogravimetry (DTG) indicated that the crosslinked esters /anhydrides might influence the thermal stability of nanocomposite samples. The UV-visible spectroscopy indicated that the nanocomposite resins possess transmittance higher than 80% in visible light region. Permeability test revealed a higher moisture permeation resistance for nanocomposite samples, which indicated that the implantation of nano-scale silica particles in polymer matrix forms effective barrier to moisture penetration. Adhesion test of nanocomposite samples on glass substrate showed at least twofold improvement of adhesion strength compared with oligomer. This evidenced that the silica and the hydrophilic segments in nanocomposite resins might form interchains hydrogen bonds with the -OH groups on the surface of glass so the substantial enhancement of adhesion strength could be achieved. (c) 2007 Wiley Periodicals, fnc.
Electron emission properties of relaxation-induced traps in InAs/GaAs quantum dots and the effect of electronic band structure
(2007-08-15)
Chen, J. F.
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Wang, J. S.
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電子物理學系
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Department of Electrophysics
The electron-emission properties of relaxation-induced traps in InAs/GaAs quantum dots (QDs) are studied in detail using capacitance-voltage (C-V) profiling and bias-dependent deep-level transient spectroscopy. Strain relaxation is shown to induce a threading-dislocation-related trap in the top GaAs layer and a misfit-dislocation-related trap near the QD. The threading trap decreases its electron-emission energy from 0.63 to 0.36 eV from sample surface toward the QD, whereas the misfit trap gradually increases its electron-emission energy from 0.28 to 0.42 eV from near the QD toward the GaAs bottom layer, indicating that both traps near the QD have lower electron-emission energies. Hence, the emission-energy change is attributed to the related traps across the QD interface where a band offset exists. The C-V profiling at 300 K shows extended carrier depletion near the QD. As temperature is increased, an electron-emission peak emerges at the QD followed by a prominent peak, suggesting that the trap responsible for the prominent peak lies in energy below the QD electron ground state. From a simulation, this trap is identified to be the misfit trap located at the QD and at the observed emission energy below the GaAs conduction band. Based on the energy location of this trap, we deduce a possible mode of strain relaxation. (C) 2007 American Institute of Physics.
Relieving Sn whisker growth driven by oxidation on Cu leadframe by annealing and reflowing treatments
(2007-08-15)
Wei, C. C.
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Liu, P. C.
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Chen, Chih
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Lee, Jeffrey C. B.
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Wang, I. Ping
Owing to environmental concern, Pb-free solders are replacing eutectic tin lead in electronic packaging industry. Thus, whisker growth becomes a serious reliability issue for Sn finishes. In this study, the mechanism of whisker growth from Sn finish on Cu leadframe was investigated under the temperature/humidity storage test. It is found that oxidation of the Sn finish was the driving force behind the whisker growth. Thermal treatments including annealing at 220 degrees C and reflowing at 260 degrees C were employed to mitigate the whisker growth. It is found that both heat treatments can significantly reduce the whisker growth rate. It is speculated that the heat treatments can relieve the residual stress in the Sn finishes and can modify their grain structure, resulting in a slower oxidation rate. Thus, they can slow down the grow rate of Sn whiskers. In addition, reflowing treatment can change the columnar grain structure of the Sn film to the equiaxed grain structure in some of its regions, resulting in a lower grain boundary diffusion rate of Sn. Therefore, the reflowed sample had the lowest growth rate of Sn whiskers. (c) 2007 American Institute of Physics.
Biocompatible and detectable carboxylated nanodiamond on human cell
(2007-08-15)
Liu, Kuang-Kai
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Cheng, Chia-Liang
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Chang, Chia-Ching
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Chao, Jui-I
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生物科技學系
Surface-modified carboxylated nanometre-sized diamond (cND) has been applied for the conjugation of biological molecules such as DNA and protein. In this study, we evaluated the biocompatibility and detection of cNDs and carbon nanotubes on human lung A549 epithelial cells and HFL-1 normal fibroblasts. Treatment with 5 or 100 nm cND particles, 0.1 - 100 mu g ml(-1), did not reduce the cell viability and alter the protein expression profile in lung cells; however, carbon nanotubes induced cytotoxicity in these cells. The cNDs particles were accumulated in A549 cells, which were observed by atomic force microscopy and laser scanning confocal microscopy. Both 5 and 100 nm cNDs particles exhibited the green fluorescence and were ingested into cells. Moreover, the fluorescence intensities were increased in cells via a concentration-dependent manner after treatment with 5 and 100 nm cNDs, which can be detected by flow cytometer analysis. The fluorescence intensities of 5 nm cNDs were relative higher than 100 nm cNDs in cells at equal concentration treatment. The observation demonstrated that cND-interacting with cell is detectable by a confocal microscope, flow cytometer and atomic force microscope. These nanoparticles may be useful for further biomedical applications based on the properties of uptake ability, detectability and little cytotoxicity in human cells.
Coaxial transitions for CPW-to-CPW flip chip interconnects
(2007-08-16)
Wu, W. C.
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Chang, E. Y.
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Huang, C. H.
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Hsu, L. H.
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Starski, J. P.
A novel coaxial transition for CPW-to-CPW flip chip interconnect is presented and experimentally demonstrated. To realise the coaxial transition on the CPW circuit, benzocyclobutene was used as the interlayer dielectric between the vertical coaxial transition and the CPW circuit. The coaxial interconnect structure was successfully fabricated and RF characterised to 67 GHz. The structure showed excellent interconnect performance from DC up to 55 GHz with low return loss below 20 dB and low insertion loss less than 0.5 dB even when the underfill was applied to the structure.
Triazole-modified calix[4]crown as a novel fluorescent on-off switchable chemosensor
(2007-08-16)
Chang, Kai-Chi
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Su, In-Hao
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Senthilvelan, Annamalai
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Chung, Wen-Sheng
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應用化學系
A novel fluorescent on-off switchable chemosensor 1 with two different types of cationic binding sites is synthesized, which is composed of a triazole-modified calix[4]crown in the 1,3-alternate conformation. Among 15 metal ions examined, the fluorescence of 1 was strongly quenched by Hg2+, Cu2+, Cr3+, and Pb2+; however, the revival of emission from the strongly quenched 1 center dot Pb2+ complex was achievable by the addition of K+, Ba2+, or Zn2+ ions. Thus, metal ion exchange can trigger an on-off switchable fluorescent chemosensor.
Solar-pumped active device
(2007-08-16)
Chi, Sien
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Chen, Nan-Kuang
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Shy, Jow-Tsong
The present invention provides a solar-pumped active device which utilizes a holographic antenna grating on a solar energy silicon substrate to select specific diffracted wavelength and couple pump wavelength in an approximately vertical way and converge the pump wavelength to excite an optical gain medium so that an optical amplifier or a laser can be obtained. The present invention requires no big size and is flexible over the surface shape and is suitable for free space optical communications on the ground and satellite optical communications. It means that the holographic antenna grating can be applied on the top floor of a building or on the glass surface of an outer wall. If it is applied to a satellite, the present invention can be deposited on a solar energy cell substrate to form a high optical amplification so that not only the electricity required in satellite optical communications can be reduced, but also a high-speed and large capacity of data can be transferred between satellites.
Unique pitch evolution in the Smectic-C-alpha(*) phase
(2007-08-17)
Liu, Z. Q.
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McCoy, B. K.
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Wang, S. T.
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Pindak, R.
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Caliebe, W.
Employing resonant x-ray diffraction, we observed unique pitch evolutions in the smectic-C-alpha* phase in mixtures of two antiferroelectric liquid crystals. Our results show that the pitch in this phase continuously evolves across 4 layers, contradicting a theoretical model that predicts that the smectic-C-FI2* phase intervenes in the smectic-C-alpha* phase. The phase sequences we found can be explained by another model that includes one type of long-range interaction among smectic layers.
COLL 483-Fabrication of phosphated TiO2 through calcination of TOPO-capped nanocrystals
(2007-08-19)
Chang, Sue-min
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Hou, Chieh-yao
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環境工程研究所
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Institute of Environmental Engineering
ENVR 173-Photoactivity of TOPO-capped TiO2 nanocrystals toward the degradation of endocrine disrupting chemicals
(2007-08-19)
Chang, Sue-min
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Lo, Pin-han
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Hou, Chieh-Yao
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環境工程研究所
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Institute of Environmental Engineering
FUEL 241-Preparation of Palladium-membrane by electroplating on AISI 316 porous stainless steel supports and its use for methanol steam reformer
(2007-08-19)
Rei, Min Hon
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Chen, Shin Chung
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Tu, George Chia
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Hung, Chia Yeh
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材料科學與工程學系
COMP 105-Prediction of Raman spectra in novel polyyne@SWNT peapods using dispersion-augmented density-functional-tight-binding
(2007-08-19)
Irle, Stephan
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Witek, Henryk A.
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Shinohara, Hisanori
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Morokuma, Keiji
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應用化學系
COLL 272-Helical morphologies in the self-assembly of chiral Schiff-based rod-coil amphiphiles
(2007-08-19)
Lin, Tz-Feng
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Ho, Rong-Ming
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Sung, Chien-Hung
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Hsu, Chain-Shu
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應用化學系
ANYL 456-Fabrication of novel molecularly imprinted alumina-silica using non-hydrolytic sol-gel method for trace phosphine detection
(2007-08-19)
Chang, Sue-min
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Hou, Ching-jung
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Yen, Shao-Yi
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Li, Shou-Nan
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環境工程研究所
INOR 65-Effect of surface and lattice vanadium ions on the physicochemical and photocatalytic properties of porous TiO2
(2007-08-19)
Chang, Sue-min
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Liu, Wei-Szu
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Sung, Pin-Hsin
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環境工程研究所
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Institute of Environmental Engineering
Volume shrinkages and mechanical properties of various fiber-reinforced hydroxyethyl methacrylate-polyurethane/unsaturated polyester composites
(2007-08-19)
Lin, Shih-Pin
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Shen, Jia-Hong
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Han, Jin-Lin
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Lee, Ya-Rong
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Yeh, Jen-Taut
Nonvolatile memory characteristics of nickel-silicon-nitride nanocrystal
(2007-08-20)
Chen, Wei-Ren
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Chang, Ting-Chang
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Liu, Po-Tsun
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Yeh, Jui-Lung
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Tu, Chun-Hao
The formation of nickel-silicon-nitride nanocrystals by sputtering a comixed target in the argon and nitrogen environment is proposed in this letter. High resolution transmission electron microscope analysis clearly shows the nanocrystals embedded in the silicon nitride and x-ray photoelectron spectroscopy also shows the chemical material analysis of nanocrystals. The memory window of nickel-silicon-nitride nanocrystals enough to define 1 and 0 states is obviously observed, and a good data retention characteristic to get up to 10 years is exhibited for the nonvolatile memory application.