Browsing by Issue Date, starting with "2009-07-06"

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Crystal symmetry breaking of wurtzite to orthorhombic in nonpolar a-ZnO epifilms
(2009-07-06)
Kuo, C. C.
;
Liu, W. -R.
;
Hsieh, W. F.
;
Hsu, C. -H.
;
Hsu, H. C.
Crystal symmetry breaking of wurtzite C-6V to orthorhombic C-2V due to in-plane anisotropic strain was investigated for nonpolar (11 (2) over bar0) ZnO epifilms grown on the R-sapphire. X-ray diffraction results reveal the epilayer is subjected to a compressive strain along the polar c-axis and tensile strains along both a-[11 (2) over bar0] surface normal and in-plane p-[1 (1) over bar 00] axis. The polarized Raman spectra of E-2 modes reveal violation of the C-6V selection rules. Oppositely, the C-2V configuration satisfies the selection rules for the Raman modes. The observed E-1 and E-2 bands in polarized optical reflection and photoluminescence spectra confirm the anisotropic strain causes the structure change to the orthorhombic one. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3159470]
交大e-News第051期
(2009-07-06)
Secretariat
;
國立交通大學秘書室
High-efficiency Q-switched dual-wavelength emission at 1176 and 559 nm with intracavity Raman and sum-frequency generation
(2009-07-06)
Chang, Y. T.
;
Chang, H. L.
;
Su, K. W.
;
Chen, Y. F.
;
電子物理學系
An efficient Q-switched dual-wavelength laser with self-frequency Raman conversion in composite Nd:YVO(4) and intracavity sum-frequency generation in BBO is reported. With an input pump power of 17.5 W, average power of 0.53 W at the first-Stokes 1176 nm and average power of 1.67 W at the sum-frequency mixed 559 nm are simultaneously generated at a pulse repetition rate of 100 kHz, corresponding to a total conversion efficiency of 12.5%. (C) 2009 Optical Society of America
Efficient high-peak-power AlGaInAs eye-safe wavelength disk laser with optical in-well pumping
(2009-07-06)
Chang, H. L.
;
Huang, S. C.
;
Chen, Yi-Fan
;
Su, K. W.
;
Chen, Y. F.
We have demonstrated an efficient high-peak-power AlGaInAs eye-safe wavelength disk laser at 1555 nm. The quantum defect and the thermal load are significantly reduced by pumping the quantum well directly. The overall conversion efficiency is enhanced over three times compared with the barrier pumping method. With a pump peak power of 3.7 kW, an output peak power of 0.52 kW is generated at a pulse repetition rate of 20 kHz. (C) 2009 Optical Society of America
Eliminate coherence spike in reflection-type pump-probe measurements
(2009-07-06)
Luo, C. W.
;
Wang, Y. T.
;
Chen, F. W.
;
Shih, H. C.
;
Kobayashi, T.
The coherence spike of femtosecond laser pulses in the reflection-type pump-probe measurements has been systematically studied in the semiconductor (100) InP. By varying the setup of the pump-probe measuring system, i.e. the polarizations of pump and probe pulses, the incident angles of pump and probe beams, and the interval of delay time between pump and probe pulses, the dramatic changes in the strength of coherence spike could be clear observed. Furthermore, the proposed methods to remove the coherence spike from the transient reflectivity curves have been demonstrated in the time-domain measurements. (C) 2009 Optical Society of America
Plasmonic-enhanced polymer photovoltaic devices incorporating solution-processable metal nanoparticles
(2009-07-06)
Chen, Fang-Chung
;
Wu, Jyh-Lih
;
Lee, Chia-Ling
;
Hong, Yi
;
Kuo, Chun-Hong
We have explored the effect of gold nanoparticle (Au NP)-induced surface plasmons on the performance of organic photovoltaic devices (OPVs). The power conversion efficiency of these OPVs was improved after blending the Au NPs into the anodic buffer layer. The addition of Au NPs increased the rate of exciton generation and the probability of exciton dissociation, thereby enhancing the short-circuit current density and the fill factor. We attribute the improvement in device performance to the local enhancement in the electromagnetic field originating from the excitation of the localized surface plasmon resonance. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3174914]
Ab initio studies of excited electronic state S(2) of pyrazine and Franck-Condon simulation of its absorption spectrum
(2009-07-07)
He, Rongxing
;
Zhu, Chaoyuan
;
Chin, Chih-Hao
;
Lin, Sheng Hsien
;
應用化學系分子科學碩博班
The equilibrium geometry and 24 vibrational-normal-mode frequencies of the excited state S(2)((1)B(2u))of pyrazine are calculated and characterized using the complete active space self-consistent field method in the adiabatic representation. The displaced harmonic oscillator approximation is used to simulate the absorption spectrum of the S(2)((1)B(2u)) state along with the Franck-Condon approximation. It is found that the totally symmetric mode v(1) plays the most important role and this exactly agrees with the experimental observations. The simulated absorption spectrum agrees well with those experimentally observed. This indicates that the present S(2)((1)B(2u)) state calculated in the adiabatic representation effectively includes contribution from the diabatic vibronic coupling through the conical intersection. (C) 2009 Elsevier B.V. All rights reserved.
Ab initio studies of excited electronic state S-2 of pyrazine and Franck-Condon simulation of its absorption spectrum
(2009-07-07)
He, Rongxing
;
Zhu, Chaoyuan
;
Chin, Chih-Hao
;
Lin, Sheng Hsien
;
應用化學系分子科學碩博班
The equilibrium geometry and 24 vibrational-normal-mode frequencies of the excited state S-2(B-1(2u))of pyrazine are calculated and characterized using the complete active space self-consistent field method in the adiabatic representation. The displaced harmonic oscillator approximation is used to simulate the absorption spectrum of the S-2(B-1(2u)) state along with the Franck-Condon approximation. It is found that the totally symmetric mode v(1) plays the most important role and this exactly agrees with the experimental observations. The simulated absorption spectrum agrees well with those experimentally observed. This indicates that the present S-2(B-1(2u)) state calculated in the adiabatic representation effectively includes contribution from the diabatic vibronic coupling through the conical intersection. (C) 2009 Elsevier B.V. All rights reserved.
Effects of polydispersity index and molecular weight on crystallization kinetics of syndiotactic polystyrene (sPS)
(2009-07-08)
Chen, Chen-Ming
;
Hsieh, Tsung-Eong
;
Ju, Ming-Yih
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Isothermal crystallization kinetics of syndiotactic polystyrene (sPS) is reported in this work with Avrami analytical method. it was found that the spherulite growth rate and overall crystallization rate depend on the crystallization temperatures, average molecular weight ((M) over bar (W)) and polydispersity index (PDI). The experimental results for the melt and cold crystallization processes of sPS revealed that the PDI and (M) over bar (W) exhibit pivotal effects on the crystallization rate, which increases with the decrease of (M) over bar (W) and PDI. (C) 2009 Elsevier B.V. All rights reserved.
Comparative Investigation of Ultrafast Photoinduced Processes in Salicylidene-Aminopyridine in Solution and Solid State
(2009-07-09)
Sliwa, Michel
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Mouton, Nicolas
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Ruckebusch, Cyril
;
Aloise, Stephane
;
Poizat, Olivier
Photodynamics and excited-state intramolecular proton transfer (ESIPT) of N-(3,5-ditert-butylsalicylidene)-4-aminopyridine (4P) and N-(3,5-ditert-butylsalicylidene)-2-aminopyridine (2P) are studied by steady-state and transient optical spectroscopy in solution and solid state (microcrystalline powder). These two compounds are representative of anils Classes A and B, respectively. The results confirm that in solution both compounds have a similar dynamic behavior: upon excitation at 390 nm, ESIPT leads to different cis-keto* fluorescent species which relax to the photochromic trans-keto photoproduct within a few tens of picoseconds. Furthermore, for the first time, picosecond data are recorded for the two classes of anils in the solid state: in 2P, two cis-keto* fluorescent excited state species (23 and 250 ps lifetime) are relaxing exclusively to the cis-keto ground state, whereas in 4P, a single cis-keto* fluorescent species is observed which leads to the trans-keto photoproduct in 250 ps via an intermediate metastable species.
Femtosecond Transient Absorption of Zinc Porphyrins with Oligo(phenylethylnyl) Linkers in Solution and on TiO2 Films
(2009-07-09)
Chang, Chih-Wei
;
Luo, Liyang
;
Chou, Chung-Kung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
We measured femtosecond transient absorption of dye solutions and TiO2 films sensitized with two zinc porphyrins (PE1 and PE4) to investigate the interfacial dynamics of electron transfer in relation to the dependence of cell performance on the length of the linker (Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C 2009, 113, 755-764). For both porphyrins adsorbed on TiO2 films with S-1 excitation (lambda(ex) = 620 nm), the transient absorption kinetics probed at 630 nm and 4.9 mu m are complementary to each other because only the excited-state and ground-state species were observed at 630 nm whereas only the charge-separation intermediates were observed at 4.9 mu m. The transient of the PE1/TiO2 film shows a single exponential decay with a large offset, whereas the transient of the PE4/TiO2 film displays a biexponential decay with a small offset. Because of the existence of an additional ps component, the amount of free delocalized electrons (offset signal) in PE4/TiO2 is smaller than that in PEI/TiO2. Our results imply that back electron transfer at the TiO2/dye interface is an important factor to be considered to account for the cell performance of a device.
Ionization and Dissociation Processes of Pyrrolidine in Intense Femtosecond Laser Field
(2009-07-09)
Wang, Qiaoqiao
;
Wu, Di
;
Zhang, Dongdong
;
Jin, Mingxing
;
Liu, Fuchun
Ionization and dissociation mechanisms of pyrrolidine in intense 800 nm laser field (10(13) to 10(14) W/cm(2)) have been experimentally investigated by using a method of molecular beam and time-of-flight mass spectrometer. Singly charged parent ion and numerous fragment ions are observed in the mass spectra, which are investigated as a function of laser intensity and polarization. In order to understand the details of the ionization processes of pyrrolidine in intense femtosecond laser field, we quantitatively calculate the rate constants and ion yields by means of generalized Keldysh-Faisal-Reiss theory, and the excitation probabilities of the excited states are also calculated by using Floquet theory. The results suggest that the ionization might occur partially through the excited states of neutral pyrrolidine. Comparing with linearly polarized (LP) laser field, we observe some enhancement of fragmentation with a circularly polarized (CP) laser field above the saturation threshold intensity which might be explained by the active energies of the pyrrolidine molecular ions are different under CP and LP laser irradiated. To interpret the dissociation patterns of the pyrrolidine ions, we have used the Rice-Ramsperger-Kassel-Marcus theory with the potential surfaces obtained from the ab initio quantum chemical calculations.
Spectral and 3-Dimensional Tracking of Single Gold Nanoparticles in Living Cells Studied by Rayleigh Light Scattering Microscopy
(2009-07-09)
Louit, Guillaume
;
Asahi, Tsuyoshi
;
Tanaka, Go
;
Uwada, Takayuki
;
Masuhara, Hiroshi
Using a confocal Rayleigh light scattering microspectroscopy and imaging system, we followed and recorded the scattering spectra of single gold nanoparticles interacting with living mouse fibroblast cells, during the scale of I h. A white light continuum produced by a femtosecond laser was focused on gold nanoparticles with a diameter of 80 nm, while an incubation system ensured viability of the living cells. After reporting spectral characteristics of gold nanoparticles and their target fibroblasts, separately and in combination, tracking sequences of single nanoparticles in contact with a single cell are described. Through the study of three separate and representative cases, transitory as well as plasmon resonance band shifts, which can be linked to biological events, have been observed and are discussed here.
Femtosecond Transient Absorption of Zinc Porphyrins with Oligo(phenylethylnyl) Linkers in Solution and on TiO(2) Films
(2009-07-09)
Chang, Chih-Wei
;
Luo, Liyang
;
Chou, Chung-Kung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
We measured femtosecond transient absorption of dye solutions and TiO(2) films sensitized with two zinc porphyrins (PE1 and PE4) to investigate the interfacial dynamics of electron transfer in relation to the dependence of cell performance on the length of the linker (Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C 2009, 113, 755-764). For both porphyrins adsorbed on TiO(2) films with S(1) excitation (lambda(ex) = 620 nm), the transient absorption kinetics probed at 630 nm and 4.9 mu m are complementary to each other because only the excited-state and ground-state species were observed at 630 nm whereas only the charge-separation intermediates were observed at 4.9 mu m. The transient of the PE1/TiO(2) film shows a single exponential decay with a large offset, whereas the transient of the PE4/TiO(2) film displays a biexponential decay with a small offset. Because of the existence of an additional ps component, the amount of free delocalized electrons (offset signal) in PE4/TiO(2) is smaller than that in PEI/TiO(2). Our results imply that back electron transfer at the TiO(2)/dye interface is an important factor to be considered to account for the cell performance of a device.
Electric Field Effects on Photoluminescence of Polyfluorene Thin Films: Dependence on Excitation Wavelength, Field Strength, and Temperature
(2009-07-09)
Mehata, Mohan Singh
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Hsu, Chain-Shu
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Lee, Yuan-Pern
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Ohta, Nobuhiro
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應用化學系
Electroabsorption (E-A) and electrophotoluminescence (E-F) spectra of thin films of blue-light-emitting poly(9,9-dioctylfluorene) (PFO) have been measured at temperatures ranging from 25 to 295 K to examine both the optical property and excitation dynamics of these films in the presence of external electric fields of 0-1.2 MV cm(-1). Electric field effects on excitation dynamics depend on not only applied field strength but also excitation wavelength and temperature. For photoexcitation at 344 or 402 nm, E-F spectra observed with low applied fields show only the Stark shift, whereas fluorescence quenching is induced only by strong electric fields. For photoexcitation at a shorter wavelength of 298 nm, on the other hand, field-induced quenching of fluorescence is observed even with a weak electric field at any temperature. The presence of a nonradiative process from highly excited states that is effectively affected by electric fields is suggested.
Image synthesis system for a vehicle and the manufacturing method thereof
(2009-07-09)
CHEN, Yong-Sheng
;
Liu, Yu-Chih
;
Lin, Kai-Ying
The present invention discloses an image synthesis system for a vehicle to provide the driver with a downward-facing image of the car's 360° surrounding view. The system includes: a first camera, which is used to shoot a first image of the periphery of the vehicle; a second camera, which is used to shoot a second image of the periphery of said vehicle, wherein the second image and the first image have an overlap region; an image processing device comprising a defining component and a synthesis component, which is used to synthesize the first image and the second image and output a third image; a display device, which is used to display the third image.
Unraveling Deterministic Mesoscopic Polarization Switching Mechanisms: Spatially Resolved Studies of a Tilt Grain Boundary in Bismuth Ferrite
(2009-07-10)
Rodriguez, Brian J.
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Choudhury, Samrat
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Chu, Y. H.
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Bhattacharyya, Abhishek
;
Jesse, Stephen
The deterministic mesoscopic mechanism of ferroelectric domain nucleation is probed at a single atomically-defined model defect: an artificially fabricated bicrystal grain boundary (GB) in an epitaxial bismuth ferrite film. Switching spectroscopy piezoresponse force microscopy (SS-PFM) is used to map the variation of local hysteresis loops at the GB and in its immediate vicinity. It is found that the the influence of the GB on nucleation results in a slight shift of the negative nucleation bias to larger voltages. The mesoscopic mechanisms of domain nucleation in the bulk and at the GB are studied in detail using phase-field modeling, elucidating the complex mechanisms governed by the interplay between ferroelectric and ferroelastic wall energies, depolarization fields, and interface charge. The combination of phase-field modeling and SS-PFM allows quantitative analysis of the mesoscopic mechanisms for polarization switching, and hence suggests a route for unraveling the mechanisms of polarization switching at a single defect level and ultimately optimizing materials properties through microstructure engineering.
Interfacial Polar-Bonding-Induced Multifunctionality of Nano-Silicon in Mesoporous Silica
(2009-07-10)
Huang, Jung Y.
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Shieh, Jia M.
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Kuo, Hao C.
;
Pan, Ci L.
;
光電工程學系
The optoelectronic response of a material governs its suitability for a wide range of applications, from photon detection to photovoltaic conversion. To conquer the material limitations and achieve improved optoelectronic responses, nanotechnology has been employed to arranges subunits with specific size-dependent quantum mechanical properties in a hierarchically organized structure. However, building a functional optoelectronic system from nano-objects remains a formidable challenge. In this paper, the fabrication of a new artificially engineered optoelectronic material by the preferential growth of silicon nanocrystals on the bottom of the pore-channels of mesoporous silica is reported. The nanocrystals form highly stable interface structures bonded on one side; these structure show strong electron-phonon coupling and a ferroelectric-like hysteretic switching property. A new class of multifunctional materials is realized by invoking a concept that employs semiconductor nanocrystals for optical sensing and utilizes interfacial polar layers to facilitate carrier transport and emulate ferroelectric-like switching.
Optimizing system capacity expansion schedules for groundwater supply
(2009-07-10)
Chang, Liang-Cheng
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Chen, Yu-Wen
;
Yeh, Ming-Sheng
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土木工程學系
;
Department of Civil Engineering
Groundwater plays a vital role in regional water resources management. In conventional design, a full-scale network system is installed initially to use groundwater resources. However, the system capacity may exceed water demand in the early stages because water demand generally increases with time. Therefore, this work proposes a novel optimal capacity expansion model capable of determining an optimal schedule to expand system capacity according to increasing water demand. The proposed algorithm hybridizes a genetic algorithm (GA) and constrained differential dynamic programming (CDDP). The chromosomes of the GA represent a possible design alternative, a groundwater network with capacity that expands with time. The CDDP algorithm is then used to compute the optimal pumping policy associated with the chromosome. Simulation results indicate that the capacity expansion model saves more total present value cost than conventional designs for the same annual interest rate and water demand. Results of this study demonstrate promise for the proposed model in facilitating a cost-effective groundwater network design with capacity expansion for regional groundwater supply.
A study on using pre-bent steel strips as seismic energy-dissipative devices
(2009-07-10)
Wang, Yen-Po
;
Chien, Chia-Shang Chang
;
土木工程學系
;
Department of Civil Engineering
Buckling is usually conceived as an unstable Structural behavior leading to lateral instability of axially loaded members, if not properly supported. However, a pre-bent strip Would become an excellent seismic energy-dissipative device it it is deformed in a guided direction and ratio, e. Geometrically large lateral deformation of the steel strips in buckling leads to inelastic behavior of the material and dissipates energy as a consequence. The purpose of this study is to propose a new type of seismic damper in the form of braces based on pre-bent steel strips. The nonlinear elastic stiffness of monotonously loaded pre-bent strips in both compression and tension is derived. The energy-dissipative characteristics of the proposed damping device are investigated via component tests under cyclic loads. Experimental results indicate that the force-displacement relationship of pre-bent strips in cyclic loads exhibits mechanical characteristics of displacement-dependent dampers. A series of seismic performance tests has been conducted further to verify the feasibility and effectiveness of using the proposed device as seismic dampers. Encouraging test results have been obtained, suggesting feasibility of the proposed device for earthquake-resistant design. Copyright (C) 2008 John Wiley & Sons, Ltd.