Browsing by Issue Date, starting with "2007-07-26"

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Ab initio chemical kinetics for the OH plus HNCN reaction
(2007-07-26)
Xu, Shucheng
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism of the reaction of the cyanomidyl radical (HNCN) with the hydroxyl radical (OH) have been investigated by ab initio calculations with rate constants prediction. The single and triplet potential energy surfaces of this reaction have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df,2p) level based on geometries optimized at the B3LYP/6-311+G(3df,2p) and CCSD/6-311++ G(d,p) levels. The rate constants for various product channels in the temperature range of 300-3000 K are predicted by variational transition-state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories. The predicted total rate constants can be represented by the expressions k(total) = 2.66 x 10(+2) x T-4.50 exp(-239/T) in which T = 300-1000 K and 1.38 x 10(-20) x T-2.78 exp(1578/T) cm(3) molecule(-1) s(-1) where T = 1000-3000 K. The branching ratios of primary channels are predicted: k(1) for forming singlet HON(H)CN accounts for 0.32-0.28, and k(4) for forming singlet HONCNH accounts for 0.68-0.17 in the temperature range of 300-800 K. k(2) + k(7) for producing H2O + NCN accounts for 0.55-0.99 in the high-temperature range of 800-3000 K. The branching ratios of k(3) for producing HCN + HNO, k(6) for producing H2N + NCO, k(8) for forming (HN)-H-3(OH)CN, k(9) for producing CNOH + (NH)-N-3, and k(5) + k(10) for producing NH2 + NCO are negligible. The rate constants for key individual product channels are provided in a table for different temperature and pressure conditions.
Computational study on the kinetics and mechanisms for the unimolecular decomposition of formic and oxalic Acids
(2007-07-26)
Chang, Jee-Gong
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Chen, Hsin-Tsung
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Xu, Shucheng
;
Lin, M. C.
;
應用化學系分子科學碩博班
The kinetics and mechanisms for the unimolecular decomposition reactions of formic acid and oxalic acid have been studied computationally by the high-level G2M(CC1) method and microcanonical RRKM theory. There are two reaction pathways in the decomposition of formic acid: The dehydration process starting from the Z conformer is found to be the dominant, whereas the decarboxylation reaction starting from the E conformer is less competitive. The predicted rate constants for the dehydration and decarboxylation reactions are in good agreement with the experimental data. The calculated CO/CO2 ratio, 13.6-13.9 between 1300 and 2000 K, is in close agreement with the ratio of 10 measured experimentally by Hsu et al. (In The 19th International Symposium on Combustion; The Combustion Institute: Pittsburgh, PA, 1983; p 89). For oxalic acid, its isomer with two intramolecular hydrogen bonds is the most stable structure, similar to earlier reports. Two primary decomposition channels of oxalic acid producing CO2 + HOCOH with barriers of 33-36 kcal/mol and CO2 + CO + H2O with a barrier of 39 kcal/mol were found. At high temperatures, the latter process becomes more competitive. The rate constant predicted for the formation of CO2 and HOCOH (the precursor of HCOOH) agrees well with available experimental data. The mechanism for the isomerization of HOCOH to HCOOH is also discussed.
A first-principles analysis for sulfur tolerance of CeO2 in solid oxide fuel cells
(2007-07-26)
Chen, Hsin-Tsung
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Choi, YongMan
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Liu, Meilin
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Lin, M. C.
;
應用化學系分子科學碩博班
The mechanism for H2S-CeO2(111) interactions in solid oxide fuel cells (SOFCs) has been investigated by using periodic density functional theory (DFT) calculations. In order to properly characterize the effect of the localization of Ce-4f states on the interactions, DFT + U calculations were applied. Adsorption of H2S, SH, and atomic S was initially examined to locate energetically favorable intermediates. The species adsorb favorably at the Ce-top, O-top, and Ce-O bridging sites, respectively. Potential energy profiles for the H2S-CeO2 (111) interactions along the three product channels producing H-2, H2O, and SO2 were constructed using the nudged elastic band (NEB) method. Calculations show that H2S weakly bounds on CeO2(111) with a small binding energy, followed by dehydrogenation processes, forming surface sulfur species with an exothermicity of 29.9 kcal/mol. Molecular-level calculations demonstrated that the SO2-forming pathway is energetically most favorable.
Computational study of reaction pathways for the formation of indium nitride from trimethylindium with HN3: Comparison of the reaction with NH3 and that on TiO2 rutile (110) Surface
(2007-07-26)
Tzeng, Yi-Ren
;
Raghunath, P.
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Chen, Szu-Chen
;
Lin, C.
;
應用化學系分子科學碩博班
The reactions of trimethylindium (TMIn) with HN3 and NH3 are relevant to the chemical vapor deposition of indium nitride thin film. The mechanisms and energetics of these reactions in the gas phase have been investigated by density functional theory and ab initio calculations using the CCSD(T)/Lanl2dz//B3LYP/Lanl2dz and CCSD(T)/Lanl2dz//MP2/Lanl2dz methods. The results of both methods are in good agreement for the optimized geometries and relative energies. These results suggest that the reaction with HN3 forms a new stable product, dimethylindiumnitride, CH3-InN-CH3 via another stable In(CH3)(2)N-3 (dimethylindium azide, DMInA) intermediate. DMInA may undergo unimolecular decomposition to form CH3InNCH3 by two main possible pathways: (1) a stepwise decomposition process through N-2 elimination followed by CH3 migration from In to the remaining N atom and (2) a concerted process involving the concurrent CH3 migration and N-2 elimination directly giving N-2 + CH3InNCH3. The reaction of TMIn with NH3 forms a most stable product DMInNH2 following the initial association and CH4-elimination reaction. The required energy barrier for the elimination of the second CH4 molecule from DMInNH2 is 74.2 kcal/mol. Using these reactions, we predict the heats of formation at 0 K for all the products and finally for InN which is 123 +/- 1 kcal/mol predicted by the two methods. The gas-phase reaction of HN3 with TMIn is compared with that occurring on rutile TiO2 (110). The most noticeable difference is the high endothermicity of the gas-phase reaction for InN production (53 kcal/mol) and the contrasting large exothermicity (195 kcal/mol) released by the low-barrier Langmuir-Hinshelwood type processes following the adsorption of TMIn and HN3 on the surface producing a horizontally adsorbed InN(a), Ti-NIn-O(a), and other products, CH4(g) + N-2(g) + 2CH(3)O(a) [J. Phys. Chem. B 2006, 110, 2263].
Comparison of geometric, electronic, and vibrational properties for isomers of small fullerenes C-20-C-36
(2007-07-26)
Malolepsza, Edyta
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Witek, Henryk A.
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Irle, Stephan
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應用化學系
;
應用化學系分子科學碩博班
We employ the self-consistent-charge density-functional tight-binding (SCC-DFTB) method for computing geometric, electronic, and vibrational properties for various topological isomers of small fullerenes. We consider all 35 five- and six-member rings containing isomers of small fullerenes, C-20, C-24, C-26, C-28, C-30, C-32, C-34, and C-36, as first part of a larger effort to catalog CC distance distributions, valence CCC angle distributions, electronic densities of states (DOSs), vibrational densities of states (VDOSs), and infrared (IR) and Raman spectra for fullerenes C-20-C-180. Common features among the fullerenes are identified and properties characteristic for each specific fullerene isomer are discussed.
Adsorption configurations and energetics of BClx (x=0-3) on TiO2 anatase (101) and rutile (110) surfaces
(2007-07-26)
Chang, Jee-Gong
;
Wang, Jenghan
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
This study investigates the adsorption and reactions of boron trichloride and its fragments (BClx) on the TiO2 anatase (101) and rutile (110) surfaces by first-principles calculations. The results show that the possible absorbates on the TiO2 anatase and rutile surfaces are very similar. The single- and double-site adsorption configurations are found for both anatase and rutile surfaces. The particular adsorbate feature on the anatase surface is its in-plane double-site adsorption by Ti and O from its sawtooth surface. The potential energy surface shows that BCl3 can be adsorbed on the O site for both the anantase and rutile surfaces and the most of the BClx reaction on both anatase and rutile surfaces are endothermic, except for the dissociative reaction on the rutile surface. The energy levels of the BClx reactions between the anatase and rutile surfaces show that the rutile surface has lower energy levels than those of anatase surface. This result reveals that the BClx dissociative adsorption more easily occurs on rutile surface than on anatase surface.
Experimental and theoretical studies of rate coefficients for the reaction O(P-3) plus C2H5OH at high temperatures
(2007-07-26)
Wu, Chih-Wei
;
Lee, Yuan-Pern
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Xu, Shucheng
;
Lin, M. C.
;
應用化學系
Rate coefficients of the reaction O(P-3) + C2H5OH in the temperature range 782-1410 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO2 at 193 nm with an ArF excimer laser; their concentrations were monitored via atomic resonance absorption. Our data in the range 886-1410 K are new. Combined with previous measurements at low temperature, rate coefficients determined for the temperature range 297-1410 K are represented by the following equation: k(T) = (2.89 +/- 0.09) x 10(-16)T(1.62) exp[-(1210 +/- 90)/T] cm(3) molecule(-1) s(-1); listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311+G(3df, 2p)//B3LYP/6-311+G(3df) level predict potential energies of various reaction paths. Rate coefficients are predicted with the canonical variational transition state (CVT) theory with the small curvature tunneling correction (SCT) method. Reaction paths associated with trans and gauche conformations are both identified. Predicted total rate coefficients, 1.60 x 10(-22)T(3.50) exp(16/T) cm(3) molecule(-1) s(-1) for the range 300-3000 K, agree satisfactorily with experimental observations. The branching ratios of three accessible reaction channels forming CH3CHOH + OH (1a), CH2CH2OH + OH (1b), and CH3CH2O + OH (1c) are predicted to vary distinctively with temperature. Below 500 K, reaction 1a is the predominant path; the branching ratios of reactions 1b,c become similar to 40% and similar to 11%, respectively, at 2000 K.
Anharmonic effect on unimolecular reactions with application to the photodissociation of ethylene
(2007-07-26)
Yao, L.
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Mebel, A. M.
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Lu, H. F.
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Neusser, H. J.
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Lin, S. H.
The importance of anharmonic effect on dissociation of molecular systems, especially clusters, has been noted. In this paper, we shall present a theoretical approach that can carry out the first principle calculations of anharmonic canonical and microcanonical rate constants of unimolecular reactions within the framework of transition state theory. In the canonical case, it is essential to calculate the partition function of anharmonic oscillators; for convenience, the Morse oscillator potential will be used for demonstration in this paper. In the microcanical case, which involves the calculation of the total number of states for the activated complex and the density of states for the reactant, we make use of the fact that both the total number of states and the density of states can be expressed in the inverse Laplace transformation of the partition functions and that the inverse Laplace transformation can in turn be carried out by using the saddle-point method. We shall also show that using the theoretical approach presented in this paper the total number of states and density of states can be determined from thermodynamic properties and the difference between the method used in this paper and the thermodynamic model used by Krems and Nordholm will be given. To demonstrate the application of our theoretical approach, we chose the photodissociation of ethylene at 157 and 193 nm as an example.
Observation of strong electron dephasing in highly disordered Cu93Ge4Au3 thin films
(2007-07-27)
Huang, S. M.
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Lee, T. C.
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Akimoto, H.
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Kono, K.
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Lin, J. J.
We report the observation of strong electron dephasing in a series of disordered Cu93Ge4Au3 thin films. A very short electron dephasing time possessing very weak temperature dependence around 6 K, followed by an upturn with further decrease in temperature below 4 K, is found. The upturn is progressively more pronounced in more disordered samples. Moreover, a lnT-dependent, but high-magnetic-field-insensitive, resistance rise persisting from above 10 K down to 30 mK is observed in the films. These results suggest a nonmagnetic dephasing process which is stronger than any known mechanism and may originate from the coupling of conduction electrons to dynamic defects.
Rovibronic bands of the (A)over-tilde <-(X)over-tilde transition of CH3OO and CD3OO detected with cavity ringdown absorption near 1.2-1.4 mu m
(2007-07-28)
Chung, Chao-Yu
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Cheng, Chi-Wen
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Lee, Yuan-Pern
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Liao, Hsin-Yi
;
Sharp, Erin N.
We have recorded several rovibronic bands of CH3OO and CD3OO in their (A) over tilde <-(K) over tilde transitions in the range of 1.18-1.40 mu m with the cavity ringdown technique. While the electronic origins for these species have been reported previously, many newly observed rovibronic bands are described here. The experimental vibrational frequencies (given as nu in the unit cm(-1) in this paper) for the COO bending (nu(8)) and COO symmetric stretching (nu(7)) modes in the (A) over tilde state are 378 and 887 cm(-1) for CH3OO, and 348 and 824 cm(-1) for CD3OO, respectively. In addition, two other vibrational frequencies were observed for the (A) over tilde state of CD3OO, namely, nu(5) (954 cm(-1)) and nu(6) (971 cm(-1)). These experimental vibrational frequencies for the A state of both CH3OO and CD3OO are in good agreement with predictions from quantum-chemical calculations at the UB3LYP/aug-cc-pVTZ level. The enhanced activity of the nu(5) vibrational mode in CD3OO is rationalized by mode mixing with the nu(7) mode, as supported by calculations of multidimensional Franck-Condon factors. In addition, many hot bands involving the methyl torsional mode (nu(12)) are observed for both normal and deuterated methyl peroxy. These bands include the "typical" sequence transitions and some "atypical" ones due to the nature of the eigenvalues and eigenfunctions which are a consequence of the low, but very different, torsional barriers in the (X) over tilde and (A) over tilde states. In addition, the 12(2)(2) band in CH3OO and the 12(3)(3) band in CD3OO show quite different structures than the origin bands, an effect which results from tunneling splittings comparable to the rotational contour. (C) 2007 American Institute of Physics.
Resonant x-ray emission spectroscopy of multiferroic TbMnO3
(2007-07-30)
Chen, J. M.
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Chen, C. K.
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Chou, T. L.
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Jarrige, I.
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Ishii, H.
The Mn 3d valence states in single-crystalline TbMnO3 were probed using x-ray absorption spectroscopy and resonant x-ray emission spectroscopy (RXES). The polarized Mn K-edge x-ray absorption spectra show a strong polarization dependence, particularly for the white line region, indicating the strong anisotropic Mn-O bonding within the ab plane in TbMnO3. The RXES data obtained at the Mn K edge clearly reveal that unoccupied Mn 3d states exhibit a relatively delocalized character, stemming from hybridization of the Mn 3d states with the neighboring Mn 4p orbitals. The authors demonstrated that resonant x-ray emission spectroscopy is able to characterize the degree of localization of the unoccupied states or hole carriers in manganites.
SrTiO3-SiO2 oxide films for possible high-k gate dielectric applications
(2007-07-31)
Lin, Chun-Chieh
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Lai, Li-Wen
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Lin, Chih-Yang
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
Amorphous thin films of SrTiO3-SiO2 high-k dielectric oxides were deposited on p-Si substrate by sputtering from the targets made by SrTiO3 and SiO2 powder mixtures. The surface morphology, crystal structure, chemical bonding configuration, and depth profile of the composition were investigated by using scanning electron microscopy, glancing incident angle X-ray diffraction, X-ray photoelectron spectroscopy, and Auger electron spectroscopy, respectively. The capacitance-voltage (CV) and current-voltage characteristics were used for demonstrating their electrical properties. The SrTiO3-SiO2 thin films remained as amorphous structures when annealed up to 900 degrees C. The Pt/SrTiO3-SiO2/Si MOS structure 2 had a low leakage current density of similar to 2 x 10(-8) A/cm(2) measured at 100 kV/cm and dielectric constant of 24 for 700 degrees C-annealed film. The films annealed at 600 degrees C showed typical CV characteristics. However, the deformed CV curves were found for films annealed at 700 degrees C due to the diffusion of Ti species in the SrTiO3-SiO2 film into the Si substrate. (C) 2006 Elsevier B.V. All rights reserved.
Liquid crystal alignment on the a-C : H films by Ar plasma ion immersion
(2007-07-31)
Chang, S. J.
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Wu, K. Y.
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Yang, Y. H.
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Hwang, J.
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Wu, Hsin-Ying
A plasma ion immersion treatment has been developed to enhance the liquid crystal (LC) alignment on the hydrogenated amorphous carbon (a-C:H) layer in an inductively coupled plasma (ICP) chamber. No LC alignment was observed for the a-C:H layer tilted at an angle of 0 degrees during the bombardment with plasma ions. The LC alignment occurs for the a-C:H layer tilted at an angle of 30 degrees or 60 degrees. Their pretilt angles (similar to 1.4 degrees) are approximately the same. The azimuthal anchoring strength is 1.98 x 10(-6) J/m(2) at a tilted angle of 30 degrees and 1.14 x 10(-4) J/m(2) at a tilted angle of 60 degrees. The mechanism for the LC alignment is attributed to the oblique incidence of ions within the matrix sheath of non-uniform thickness near the a-C: H surface under a negative pulse bias. The matrix sheath of non-uniform thickness is confirmed by the plasma density distribution in the ICP chamber and the X-ray photoemission spectra across the a-C:H layer. (C) 2007 Elsevier B.V. All rights reserved.
VLSI architecture for the low-computation cycle and power-efficient recursive DFT/IDFT design
(2007-08-01)
Van, Lan-Da
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Lin, Chin-Teng
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Yu, Yuan-Chu
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資訊工程學系
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電控工程研究所
In this paper, we propose one low-computation cycle and power-efficient recursive discrete Fourier transform (DFT)/inverse DFT (IDFT) architecture adopting a hybrid of input strength reduction, the Chebyshev polynomial, and register-splitting schemes. Comparing with the existing recursive DFF/IDFI' architectures, the proposed recursive architecture achieves a reduction in computation-cycle by half. Appling this novel low-computation cycle architecture, we could double the throughput rate and the channel density without increasing the operating frequency for the dual tone multi-frequency (DTMF) detector in the high channel density voice over packet (VoP) application. From the chip implementation results, the proposed architecture is capable of processing over 128 channels and each channel consumes 9.77 mu W under 1.2 V@20MHz in TSMC 0.13 IP8M CMOS process. The proposed VLSI implementation shows the power-efficient advantage by the low-computation cycle architecture.
Run-by-run process control of metal sputter deposition: Combining time series and extended kalman filter
(2007-08-01)
Chen, Juhn-Horng
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Kuo, Tzu-Wei
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Lee, An-Chen
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機械工程學系
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Department of Mechanical Engineering
Subtopic segmentation for small corpus using a novel fuzzy model
(2007-08-01)
Chang, Tao-Hsing
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Lee, Chia-Hoang
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資訊工程學系
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Department of Computer Science
Subtopic segmentation is a critical task in numerous applications, including information retrieval, automatic summarization, essay scoring, and others. Although several approaches have been developed, many are ineffective for specific domains with a small corpus because of the fuzziness of the semantics of words and sentences in the corpus. This paper explores the problem of subtopic segmentation by proposing a fuzzy model for the semantics of both words and sentences. The model has three characteristics. First, it can deal with the uncertainty in the semantics of words and sentences. Secondly, it can measure the fuzzy similarity between the fuzzy semantics of sentences. Thirdly, it can develop a fuzzy algorithm for segmenting a text into several subtopic segments. The experiments, especially for a short text with a small corpus in a specific domain, indicate that the method can efficiently increase the accuracy of subtopic segmentation over previous methods.
Aberration analysis of a wedge-plate display system
(2007-08-01)
Cheng, Yi-Kai
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Chung, Sen-Nien
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Chern, Jyh-Long
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光電工程學系
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Department of Photonics
The aberration characteristics of a wedge-plate display optical system are analyzed. The study shows that a kink-like feature is inherent in the ray-intercept curve due to either the onset of the dark zone in imaging or the coincidence of the ray direction with the vertex. Third-order aberration coefficients are deduced, and the total amount of aberration is investigated to illustrate the basic limitations of image quality in this type of display. The issue of design optimization is also investigated based on the aberration characteristics. A numerical example of a 50 in. display with a 1:10 thickness and a diagonal screen length ratio is also provided. (c) 2007 Optical Society of America.
Dichotomy of photoinduced quasiparticle on CuO2 planes of YBa2Cu3O7 directly revealed by femtosecond polarization spectroscopy
(2007-08-01)
Luo, C. W.
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Chen, L. Y.
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Lee, Y. H.
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Wu, K. H.
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Juang, J. Y.
The dichotomy of photoinduced quasiparticle dynamics in the anisotropic high T, superconductors (YBa2CU3O7) is revealed by using the orientation-resolved ferntosecond reflection spectroscopy in the specially designed thin films. The transient reflectivity Delta R/R along the ab diagonal and b axis are totally different in the slow relaxation process which relates to the opening of the superconducting gap. In addition, the distribution of the temperature evolution of Delta R/R on the CuO2 planes of YBa2Cu3O7 may indicate the d-wave symmetry of the superconducting gap in high T, superconductors. (c) 2007 American Institute of Physics.
High-resolution through-focus metric with two-pitch grating target
(2007-08-01)
Shyu, Deh-Ming
;
Lu, Mao-Hong
;
Ko, Chun-Hung
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光電工程學系
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Department of Photonics
Through-focus focus-metric is a method that is used to analyze images on a fixed plane with the help of focus-metric values when the target moves through the focus. In this study, an optical microscope having a magnification of 250x is constructed. A two-pitch grating target is imaged on a CCD detector and through-focus image data are measured. In addition, the optical field on the CCD detector is simulated using the boundary element method and physical optics propagation. By comparing the measured focus-metric signatures with the simulated signatures, information regarding the linewidth is obtained. The results show that the through-focus focus-metric method is a very sensitive method that can be used for measuring parameters such as the linewidth. Thus, a nanoscale resolution can be achieved. (C) 2007 Elsevier B.V. All rights reserved.
Data hiding in binary images with distortion-minimizing capabilities by optimal block pattern coding and dynamic programming techniques
(2007-08-01)
Lee, I-Shi
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Tsai, Wen-Hsiang
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資訊工程學系
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Department of Computer Science
A new method for data hiding in binary images based on block pattern coding and dynamic programming with distortion-minimizing capabilities is proposed. Up to three message data bits can be embedded into each 2 x 2 block in an input image by changing the block's pixel pattern into another, which represents the value of the message data bits as a code according to a block pattern encoding table. And extraction of hidden message data is accomplished by block pattern decoding. To minimize the resulting image distortion, two optimization techniques are proposed. The first is to use multiple block pattern encoding tables, from which an optimal one is selected specifically for each input image, and the second is to use a dynamic programming algorithm to divide the message data into bit segments for optimal embedding in a sense of minimizing the number of binary bit flippings. Accordingly, not only more data bits can be embedded in an image block on the average, but the resulting image distortion is also reduced in an optimal way. Experimental results are also included to show the effectiveness of the proposed approach.