Browsing by Issue Date, starting with "2004-02-06"

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Comment on "Triplet-to-singlet exciton formation in poly(p-phenylene-vinylene) light-emitting diodes" - Reply
(2004-02-06)
Lin, LC
;
Meng, HF
;
Shy, JT
;
Horng, SF
;
Yu, LS
A new trans-to-cis photoisomerization mechanism of azobenzene on the S-1(n,pi*) surface
(2004-02-12)
Diau, EWG
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
;
Institute of Molecular science
The rotation-inversion controversy for the photoisomerization mechanism of azobenzene has been addressed on the basis of the CASSCF calculations for the excited-state relaxed surface scan along the CNN bending (inversion), the CNNC torsion (rotation), and the concerted CNN bending (concerted inversion) reaction pathways. According to our calculated results, the inversion channel involves a substantial energy barrier and a large S-0-S-1 energy gap so that it is a highly unfavorable channel to be considered for an efficient electronic relaxation. The rotation channel is essentially barrierless with a conical intersection close to the midpoint of the pathway to reasonably account for the subpicoseond to picosecond relaxation times observed in recent ultrafast experiments. Along the concerted inversion reaction path, a sloped conical intersection (S-0/S-1 CI_inv) was found to have the geometry close to a linear CNNC configuration. When the photoexcitation occurs in the S-2 state, the concerted inversion channel may be open and the S-0/S-1 CI_inv would become energetically accessible to produce more trans-S-0 isomers. A new mechanism is proposed to rationalize the early experimental results for the following two cases: (1) the trans-to-cis photoisomerization quantum yields on S-2 excitation are much lower than the yields on S-1 excitation; (2) the yields from both the S-2 and the S-1 excitations become essentially equal when the rotation channel is blocked by chemical modification or in an inclusion complex.
Electrical and dielectric behavior of fluorite-like Sr0.8Bi2.6Ta2O9 thin films pyrolyzed and thermally annealed at 450 degrees C
(2004-02-15)
Huang, CH
;
Chou, HY
;
Lian, CW
;
Tseng, TY
;
電子工程學系及電子研究所
In this paper, we present the results of the fabrication and characterization of fluorite-like Sr0.8Bi2.6Ta2O9 (SBT) thin films spin-coated on Ir (50 nm)/SiO2 (100 nm)/p-type (100)Si substrates using the metal-organic decomposition (MOD) technique. The SBT films prepared at 450 degreesC under various annealing times were characterized by X-ray diffraction (XRD) as fluorite phase. The polarization versus electric field (P-E) behavior of SBT thin films pyrolyzed and annealed at 450degreesC for 60 min was linear with dielectric constant of 100. The 450 degreesC annealed films have the leakage current density of about 4 x 10(-8) A/cm(2) at 200 kV/cm. The dependence of cumulative failure on dielectric breakdown field and time-dependent dielectric breakdown studies for these paraelectric SBT films indicated that the longer the annealing time, the better the breakdown field, whereas the film with no annealing treatment had a lifetime of over 10 years on operation at the electric field of 0.8 MV/cm. (C) 2003 Elsevier B.V. All rights reserved.
MOCVD growth of AlN/GaN DBR structures under various ambient conditions
(2004-02-15)
Yao, HH
;
Lin, CF
;
Kuo, HC
;
Wang, SC
;
光電工程學系
The high-reflectivity AlN/GaN distributed Bragg reflector (DBR) structures were realized by metal organic chemical vapor deposition (MOCVD) growth under pure N-2 ambient for AlN epilayer growth. The highest peak reflectivity of about 94.5% with a stopband width of 18 nm at a center wavelength of 442 nm was obtained. For the DBR structure with AIN layer grown under mixture of N-2/H-2 and pure H-2 conditions, the center wavelength was blue-shifted to 418 and 371 nm and the peak reflectivity also showed a reduction to 92% and 79%, respectively. The stopband width also decreases with increasing H-2 contents. The surface roughness and the grain size of the grown DBR structures showed an increase with increasing the H-2 ambient gas ratio. For realization of a high reflectivity and broad bandwidth of AlN/ GaN DBR by using the MOCVD growth method, the pure N-2d ambient gas for growth of AIN layer should be preferable and optimal condition. (C) 2003 Elsevier B.V. All rights reserved.
Self-rated health among young people with type 1 diabetes in relation to risk factors in a longitudinal study
(2004-02-15)
Huang, GH
;
Palta, M
;
Allen, C
;
LeCaire, T
;
D'Alessio, D
Care for type 1 diabetes mellitus should both alleviate the physical complications of the disease and improve overall quality of life. The Wisconsin Diabetes Registry, comprising a population-based cohort that is followed longitudinally from diagnosis of type 1 diabetes, provided the authors with a unique opportunity to examine quality of life in children, adolescents, and young adults with type 1 diabetes and its relation to both sociodemographic and clinical risk factors. The authors analyzed data from 1987-2002 with a mean of 10.2 years' duration of diabetes (n = 569). They used ordinal-scaled self-rated global health as a measure of quality of life. In this paper, they propose a random-effects model for drawing inferences on individuals regarding the relation of longitudinally measured quality of life to multiple risk factors. Results showed that male gender, higher parental socioeconomic level, younger age at diabetes diagnosis, shorter diabetes duration, no hospitalization in the preceding 6 months, lower glycosylated hemoglobin level, and questionnaire responses by a person other than the subject were independently associated with better reported health. The authors found that individuals varied in their reported health even after adjustment for all identified risk factors. This could imply either that there is variability in perception even with the same health status or that there are independent unmeasured risk factors for poor health in persons with type 1 diabetes.
Controlled placement of self-organized Ge dots on patterned Si (001) surfaces
(2004-02-15)
Lee, HM
;
Yang, TH
;
Luo, GL
;
Chang, EY
;
材料科學與工程學系
The positioning and ordering of the self-organized Ge dots were controlled using the ultra high-vacuum chemical molecular epitaxial growth of Ge on electron beam lithographically patterned Si (001) substrates. The experimental results indicate that the edge smoothness of the etched Si holes affects the distribution and long-range ordering of the Ge dots formed. With optimized etching conditions, the Ge dots can be grown uniformly on the edges of the holes etched on the patterned Si substrates. The sizes of the Ge dots are approximately 10 nm. The proposed, technique can be applied to the fabrication of regimented arrays in signal processing applications.
Spatially-resolved photoluminescence studies of V-shaped pits on Al0.16Ga0.84N
(2004-02-15)
Huang, HY
;
Ku, CS
;
Ke, WC
;
Tang, NE
;
Peng, JM
We have studied optical properties of V-shaped pits on Al0.16Ga0.84N. The microphotoluminescence spectrum from the pit center shows a broader and stronger emission at 350 nm than the near-band-edge emission at 336 nm from nonpit regions. The results indicated specific defect levels associated with the V-shaped pits. Furthermore, after using atomic force microscopy to probe the surface electrical potential with a conductive tip, the pit's potential was similar to0.2 V lower than its surrounding region. A simplified energy diagram is tentatively proposed to interpret our observation. (C) 2004 American Institute of Physics.
Ultra-high-density InGaN quantum dots grown by metalorganic chemical vapor deposition
(2004-02-15)
Tu, RC
;
Tun, CJ
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Chuo, CC
;
Lee, BC
;
Tsai, CE
This study examined how the duration of SiNx treatment on an underlying GaN layer affects the optical property, surface morphology and density of following InGaN quantum dots (QDs). InGaN QDs with extremely high density of near 3 x 10(11) cm(-2) exhibited strong photoluminescence (PL) emission at room temperature (RT). Increasing the duration of the SiN, treatment of the underlying GaN layer, the RT-PL peak of the following InGaN nano-islands and QDs was found to be red-shifted from the violet to the greenish region, and the spectrum was broadened. Additionally, the average height of InGaN nano-islands and QDs increased with the duration of SiNs treatment, explaining the redshift of the RT-PL peak.
High nitrogen content InGaAsN/GaAs single quantum well for 1.55 mu m applications grown by molecular beam epitaxy
(2004-02-15)
Wang, JS
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Kovsh, AR
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Hsiao, RS
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Chen, LP
;
Chen, JF
The growth of high nitrogen content InGaAsN/GaAs single quantum well (SQW) for 1.55 mum applications on GaAs substrates using solid source molecular beam epitaxy and radio frequency plasma nitrogen source is reported. The nitrogen composition was determined using an X-ray diffractometer combined with dynamic simulation. The crystal and optical qualities of highly strained InGaAs/GaAs SQW grown at low temperature can be significantly improved by nitrogen incorporation due to reducing the lattice mismatch. Without the formation of additional nonradiative recombination in InGaAsN SQW with nitrogen composition up to 4.1% which corresponds to wavelength of 1.46 mum was achieved. The longest room-temperature PL peak wavelength obtained in this study is 1.59 mum by increasing the nitrogen composition up to 5.3%. And, the photoluminescence intensity of high nitrogen content InGaAsN SQW can be improved significantly by decreasing the growth temperature due to suppression of the phase separation of InGaAsN alloy. Our results show the potential for the fabrication of 1.55 mum InGaAsN QW lasers on GaAs substrates. (C) 2003 Elsevier B.V. All rights reserved.
Complex fiber grating structures fabricated by sequential writing with polarization control
(2004-02-15)
Chu, KP
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Lai, YC
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Sheu, LG
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光電工程學系
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Department of Photonics
We propose a flexible method for fabricating complex fiber grating structures based on sequential writing for fiber gratings with polarization control of the UV source beam. Pure apodized as well as arbitrary phase-shifted fiber Bragg gratings (FBGs) can be fabricated in a single scan. Experimental examples of raised-cos(2) apodized and dispersionless FBG filters are given to demonstrate the feasibility of this method. (C) 2004 Optical Society of America.
史記
(2004-02-15)
管管
Characterization of poly(vinyl pyrrolidone-co-isobutylstyryl polyhedral oligomeric silsesquioxane) nanocomposites
(2004-02-15)
Xu, HY
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Kuo, SW
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Huang, CF
;
Chang, FC
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應用化學系
Poly(vinyl pyrrolidone-co-isobutyl styryl polyhedral oligomeric silsesquioxane)s (PVP-POSS) were synthesized by one-step polymerization and characterized 13 using FTIR, high-resolution H-1-NMR, solid-state C-13-NMR, Si-29-NMR, GPC, and DSC. The POSS content can be controlled by varying the POSS feed ratio. The T-g of the PVP-FOSS hybrid is influenced by three main factors: (1) a diluent role of the POSS in reducing the self-association of the PVP; (2) a strong interaction between the POSS siloxane and the PVP carbonyl, and (3) physical aggregation of nanosized POSS. At a relatively low FOSS content, the role as diluent dominates, resulting in a decrease in T-g. At a relatively high POSS content, the last two factors dominate and result in T-g increase of the PVP-POSS hybrid. (C) 2003 Wiley Periodicals, Inc.
Spin-dependent Hall effect in semiconductor quantum wells
(2004-02-15)
Huang, HC
;
Voskoboynikov, O
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Lee, CP
;
交大名義發表
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National Chiao Tung University
We present a theoretical study of the spin-dependent scattering of electrons from screened attractive and repulsive impurities in III-V semiconductor quantum wells. The effective one-band Hamiltonian and the Rashba spin-orbit interaction are used. We demonstrated that the asymmetry of the spin-dependent skew-scattering and side-jump effect can lead to a quite large spin-dependent (anomalous) Hall effect at zero magnetic field in all-semiconductor quantum well structures. Our theory predicts a measurable spin-dependent Hall angle that reaches about 2.5x10(-3) rad for a CdTe/InSb/CdTe quantum well with impurities doped in the center of the well. (C) 2004 American Institute of Physics.
Experimental and quantum-chemical studies on photoionization and dissociative photoionization of CH2Br2
(2004-02-15)
Chiang, SY
;
Fang, YS
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Sankaran, K
;
Lee, YP
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應用化學系
The dissociative photoionization of CH2Br2 in a region similar to10-24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH2Br2 agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH2Br+, CHBr+, and CBr+ show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr2+, Br+, and CH2+ appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH2Br2 are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of DeltaH(f,298)(0)(CHBr+)less than or equal to300.7+/-1.5 kcal mol(-1) is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be less than or equal to9.17+/-0.23 eV. Literature values for DeltaH(f,298)(0)(CBr+)=362.5 kcal mol(-1) and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol(-1) and 9.11 eV, respectively. Also based on a new experimental ionization energy, DeltaH(f,298)(0)(CH2Br2+) is revised to be 236.4+/-1.5 kcal mol(-1). (C) 2004 American Institute of Physics.
Designing and implementing a new type of transport-layer socket: the UDTCP socket case
(2004-02-15)
Wang, SY
;
資訊工程學系
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Department of Computer Science
On most operating systems, the UDP and TCP sockets are the two main types of sockets used to provide transport-layer networking services. However, for several reasons, UDP and TCP sockets are unsuitable for transporting delay-sensitive but error-tolerant streaming data such as the data generated by multimedia streaming applications. In this paper, we create a new type of socket that is suitable for transporting such data and propose a novel and simple implementation for it. We have implemented this new type of socket in Free BSD 4.8 and call it the 'UDTCP socket.' It has both the UDP and TCP socket properties suitable for delay-sensitive but error-tolerant streaming data but not those UDP and TCP socket properties unsuitable for such data. When transporting a stream of such data whose sending rate needs to be regulated by TCP congestion control, our simulation results show that the UDTCP socket can provide a much better delay and delay-jitter performance than the TCP socket. (C) 2003 Elsevier B.V. All rights reserved.
Color-tunable multilayer light-emitting diodes based on conjugated polymers
(2004-02-16)
Huang, CC
;
Meng, HF
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Ho, GK
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Chen, CH
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Hsu, CS
Wide-range low-voltage continuous color tuning is achieved in multilayer light-emitting diodes based exclusively on the commonly used high-efficiency electroluminescent conjugated polymers. There are three layers for red, green, and blue emission, and one extra layer for electron blocking. The color of the emitted photon depends on the position of the electron-hole recombination. Due to the stronger field dependence of the electron mobility relative to the hole mobility, the recombination zone is pushed away from the cathode and concentrated in different emissive layers as the voltage increases. (C) 2004 American Institute of Physics.
Electronic transport in insulating AlPdRe quasicrystals
(2004-02-18)
Rosenbaum, R
;
Murphy, T
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Brandt, B
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Wang, CR
;
Zhong, YL
Resistivity and magnetoresistance measurements have been performed on insulating icosahedral AlPdRe quasicrystal (QC) bar samples. At temperatures in the range 300 K greater than or equal to T greater than or equal to 50 K, the resistivities follow a simple inverse temperature law: rho(T) rho(0)/T(1.0+/-0.1). Below 1 K, the resistivity of a weakly insulating sample exhibited a simple inverse temperature law where rho(T) = rho0/T-0.33 and not an activated variable-range hopping (VRH) law. Strongly insulating samples exhibit saturation of their resistivities to finite values as T --> 0 K. These saturation resistivity values are believed to arise from the presence of a second metallic phase located within the quasicrystal's structure. By extrapolating the measured resistivities at 22 mK to absolute zero, the saturation conductivity values were estimated at T = 0 K and subtracted from the conductivity data points. These 'corrected' data, corresponding only to the QC phase, were found to follow activated VRH laws, having hopping exponents y that vary in the range 0.18 less than or equal to y less than or equal to 0.43. The activated VRH behaviours are observed only below 1 K. The magnetoresistances (MRs) of these samples are also anomalous. The MRs can be explained by including contributions from both the saturation conductivity values and from the QC MR ratios, estimated using the wavefunction shrinkage model.
Double-layer networks with holographic optical switches
(2004-02-20)
Deng, JS
;
Lu, MF
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Huang, YT
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
The double-layer networks have the advantages of being strictly nonblocking and having a simpler routing algorithm, the lowest system insertion loss, a zero differential loss, fewer drivers, fewer interconnection lines, fewer crossovers, and the best signal-to-noise-ratio characteristic compared with any nondilated network. Using holographic optical switches to construct these networks not only eliminates all interconnection lines and crossovers but also reduces the number of drivers. (C) 2004 Optical Society of America.
Multi-port polarization-independent optical quasi-circulators by using a pair of holographic spatial- and polarization-modules
(2004-02-23)
Chen, JH
;
Hsieh, PJ
;
Su, DC
;
Su, JC
;
光電工程學系
In this paper we proposed an alternative type of multi-port polarization-independent optical quasi-circulator by using a pair of holographic spatial- and polarization-modules. The prototype is fabricated and experimentally tested. In addition, the operating principles, the characteristics and the performances of this device are discussed. The merits of this design include polarization-independence, compactness, high isolation, low polarization mode dispersion, and easy fabrication. Furthermore, the number of ports can be scaled up easily. (C) 2004 Optical Society of America.
Sub femto-joule sensitive single-shot OPA-XFROG and its application in study of white-light supercontinuum generation
(2004-02-23)
Zhang, JY
;
Lee, CK
;
Huang, JY
;
Pan, CL
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光電工程學系
We report a new design of single-shot cross-correlation frequency-resolved optical gating (XFROG) with sub femto-joule sensitivity for complete field characterization of ultrashort optical pulse using a 400-nm-pumped type-I noncollinear optical parametric amplifier. Optical parametric gain as high as 10(8) with 0.8-0.9 femto-joules sensitivity had been demonstrated with an un-cooled CCD in this study. The experimental FROG traces have been successfully retrieved with an error no worse than 0.0014. The device had been to be useful for studying the generation mechanism of white-light supercontinuum (WLS). (C) 2004 Optical Society of America.