Browsing by Issue Date, starting with "2009-04-22"

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Fluorescence signals of core-shell quantum dots enhanced by single crystalline gold caps on silicon nanowires
(2009-04-22)
Christiansen, S. H.
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Chou, J. W.
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Becker, M.
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Sivakov, V.
;
Ehrhold, K.
We use nanoscale (20-300 nm in diameter) single crystalline gold (Au)-caps on silicon nanowires (NWs) grown by the vapor-liquid-solid (VLS) growth mechanism to enhance the fluorescence photoluminescence (PL) signals of highly dilute core/shell CdSeTe/ZnS quantum dots (QDs) in aqueous solution (10(-5) M). For NWs without Au-caps, as they appear, for example, after Au etching in aqua regia or buffered KI/I(2)-solution, essentially no fluorescence signal of the same diluted QDs could be observed. Fluorescence PL signals were measured using excitation with a laser wavelength of 633 nm. The signal enhancement by single crystalline, nanoscale Au-caps is discussed and interpreted based on finite element modeling (FEM).
Design and Structural Analysis of Novel Pharmacophores for Potent and Selective Peroxisome Proliferator-activated Receptor gamma Agonists
(2009-04-23)
Lin, Chia-Hui
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Peng, Yi-Hui
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Coumar, Mohane Selvaraj
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Chittimalla, Santhosh Kumar
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Liao, Chun-Chen
Utilizing medicinal chemistry design strategies Such as benzo splitting and ring expansion, we converted PPAR alpha/gamma dual agonist 1 to selective PPAR gamma agonists 19 and 20. Compounds 19 and 20 were 2- to 4-fold better than rosiglitazone at PPAR gamma receptor. with 80- to 100-fold PPAR gamma selectivity over PPAR alpha receptor. X-ray cocrystal studies in PPAR gamma and modeling studies in PPAR alpha give molecular insights for the improved PPAR gamma potency and selectivity for 19 when compared to 1.
Dynamics of the F-2 Reaction with Propene: The Effect of Methyl Substitution
(2009-04-23)
Fang, Jing-Wen
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Xie, Tingxian
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Chen, Hsueh-Ying
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Lu, Yu-Ju
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Lee, Yuan T.
The reaction of F-2 + C3H6 has been investigated with the crossed molecular beam technique. The only observed primary product channel is F + C3H6F while the HF + C3H5F channel cannot be found. The reaction cross section was measured as a function of collision energy and the reaction threshold was determined to be 2.4 +/- 0.3 kcal/mol. Compared to the reaction threshold of the F-2 + C2H4 reaction, the methyl substitution effectively reduces the reaction threshold by about 3 kcal/mol. The product time-of-flight spectra and angular distributions were measured and analyzed. The angular distribution displays strongly backward, indicating that the reaction is much faster than rotation. All experimental results support a rebound reaction mechanism, which agrees with the structure of the calculated transition state. The transition state geometry also suggests an early barrier; such dynamics is consistent with the observed small kinetic energy release of the products. Except for the different values of the reaction thresholds, the dynamics of the F-2 + C2H4 and F-2 + C3H6 reactions are remarkably similar.
Mechanism of Ethanol Reforming: Theoretical Foundations
(2009-04-23)
Wang, Jeng-Han
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Lee, C. S.
;
Lin, M. C.
;
應用化學系
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應用化學系分子科學碩博班
The mechanism of ethanol reforming has been systematically studied by both energetic calculation to examine ethanol decomposition and electronic structure analysis to investigate the redox capability of the nine selected metals of Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au with the same crystal structure and surface orientation. The energetic calculation shows that most of the dissociation barriers are lower on Co(111), Ni(111), Rh(111), and Ir(111.) surfaces and higher on Cu(111), Ag(111), and Au(111) surfaces. The initial C-H bond dissociation, forming the doubly adsorbed *C(H(2))C(H(2))O(H)* and *C(H(2))C(H(2))O*, with a lower barrier than those in the initial C-C and C-O bond dissociations is considered as the most feasible decomposition route. In addition, the linear correlation between reaction barriers and d-band centers breaks down in the case of C-H bond dissociation due to the lower barriers on Rh(111) and Ir(111) surfaces. This result may be related to the suitable bond distances on Rh(111) and Ir(111) surfaces to form the more stable double adsorbates, *C(H(2))C(H(2))O(H):* and *C(H(2))C(H(2))O*. In the electronic structure analysis, Rh(111) and Ir(111) surfaces with higher density of state (DOS) distributions around the Fermi level can efficiently accept/donate electrons from/to the reacting ethanol and its fragments, showing better redox capability. Therefore, the excellent efficiency of Rh- and Ir-based catalysts, as observed from the reforming experiment, can be attributed to both the lower decomposition barrier and the higher DOS distribution around the Fermi level based on the first-principles calculation.
Vertical Phase Separation in Poly(3-hexylthiophene): Fullerene Derivative Blends and its Advantage for Inverted Structure Solar Cells
(2009-04-23)
Xu, Zheng
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Chen, Li-Min
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Yang, Guanwen
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Huang, Chun-Hao
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Hou, Jianhui
A method which enables the investigation of the buried interfaces without altering the properties of the polymer films is used to study vertical phase separation of spin-coated poly(3-hexylthiophene) (P3HT):fullerene derivative blends. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis reveals the P3HT enrichment at the free (air) surfaces and abundance of fullerene derivatives at the organic/substrate interfaces. The vertical phase separation is attributed to the surface energy difference of the components and their interactions with the substrates. This inhomogeneous distribution of the donor and acceptor components significantly affects photovoltaic device performance and makes the inverted device structure a promising choice.
Dynamics of the F(2) Reaction with Propene: The Effect of Methyl Substitution
(2009-04-23)
Fang, Jing-Wen
;
Xie, Tingxian
;
Chen, Hsueh-Ying
;
Lu, Yu-Ju
;
Lee, Yuan T.
The reaction of F(2) + C(3)H(6) has been investigated with the crossed molecular beam technique. The only observed primary product channel is F + C(3)H(6)F while the HF + C(3)H(5)F channel cannot be found. The reaction cross section was measured as a function of collision energy and the reaction threshold was determined to be 2.4 +/- 0.3 kcal/mol. Compared to the reaction threshold of the F(2) + C(2)H(4) reaction, the methyl substitution effectively reduces the reaction threshold by about 3 kcal/mol. The product time-of-flight spectra and angular distributions were measured and analyzed. The angular distribution displays strongly backward, indicating that the reaction is much faster than rotation. All experimental results support a rebound reaction mechanism, which agrees with the structure of the calculated transition state. The transition state geometry also suggests an early barrier; such dynamics is consistent with the observed small kinetic energy release of the products. Except for the different values of the reaction thresholds, the dynamics of the F(2) + C(2)H(4) and F(2) + C(3)H(6) reactions are remarkably similar.
Detection of an uncharged steroid with a silicon nanowire field-effect transistor
(2009-04-24)
Chang, Ko Shing
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Chen, Chen Chia
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Sheu, Jeng Tzong
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Li, Yaw-Kuan
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材料科學與工程學系奈米科技碩博班
Among biosensors of various types, the silicon nanowire field-effect transistor (SiNW-FET) is believed to be the most sensitive and powerful device for bio-applications. The principle of sensing is based on the variation of conductivity resulting from a disturbance of charge on the surface of the SiNW-FET, but this detection is feasible predominantly for charged analytes, such as a protein, DNA, antibody, virus etc. The objective of our work was to overcome this intrinsic weakness of a SiNW-FET and to develop a platform to detect steroids. For this purpose, we designed an engineered protein. Delta(5)-3-ketosteroid isomerase, to function as a steroid acceptor that was chemically modified with a carbon chain-linked 1,5-EDANS moiety, and further immobilized on the surface of a silicon nanowire. In the presence of a steroid, the negatively charged 1,5-EDANS moiety, which presumably occupies the steroid-binding site, is expelled and exposes to the nanowire surface. The electrical response produced from the 1,5-EDANS moiety is measured and the concentration is calculated accordingly. The sensitivity of this novel nano-bio-device can attain a femtomolar level. (C) 2009 Elsevier B.V. All rights reserved.
RF phase shifter using a distributed feedback laser in microwave transport systems
(2009-04-27)
Peng, Peng-Chun
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Wu, Fang-Ming
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Jiang, Wen-Jr
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Lan, Ruei-Long
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Lin, Chun-Ting
This work experimentally demonstrates the efficacy of a radio-frequency phase shifter using a distributed feedback laser in a microwave transport system. Phase shifts of about 101 are obtained at 8.75GHz. The proposed phase shifter can amplify microwave signals and thereby improve transmission performance. Additionally, a similar single sideband modulation can be generated by the phase shifter. Experimental results indicate that the proposed phase shifter can be used in future long-distance microwave transport systems and all optical inverters. (C) 2009 Optical Society of America
Electrical properties of single and multiple poly(3,4-ethylenedioxythiophene) nanowires for sensing nitric oxide gas
(2009-04-27)
Lu, Hui-Hsin
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Lin, Chia-Yu
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Hsiao, Tzu-Chien
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Fang, Yueh-Yuan
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Ho, Kuo-Chuan
The electrical properties of conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), nanowires were studied to develop nitric oxide (NO) gas sensors with low working temperatures. A nanowire with a diameter of 300 nm was fabricated using dip-pen nanolithography (DPN) across a 55 mu m gap between a pair of electrodes. The electrical properties of single or multiple PEDOT nanowires were examined by plotting the current-voltage (I-V) curves in the range -3 V to +3 V at temperatures between 298 K and 393 K. The conductance of parallel wires was normalized with respect to the dimensions of the fabricated nanowires. The single nanowire exhibited nonlinear conductance associated with hysteresis but multiple wires did not. The currents increased with the temperature and the I-V characteristics were consistent with the power lawG(T)alpha T(alpha) with alpha similar to 5.14 and 5.43. The responses to NO were highly linear and reproducible, indicating that sensing using PEDOT nanowires was reliable with a minimal concentration of NO of 10 ppm. (c) 2009 Elsevier B.V. All rights reserved.
Efficiency Enhancement of GaAs Photovoltaics Employing Antireflective Indium Tin Oxide Nanocolumns
(2009-04-27)
Yu, Peichen
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Chang, Chia-Hua
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Chiu, Ching-Hua
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Yang, Chin-Sheng
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Yu, Jue-Chin
Highly-oriented indium tin oxide nano-columns are prepared by glancing-angle deposition with nitrogen. The tapered column profiles, which function as a graded-refiractive-index layer, offer superior antireflective characteristics. The nano-structured material serves as the conductive antireflective layer for GaAs solar cells, demonstrating a viable efficiency-boosting strategy for next-generation photovoltaics.
Stored don't-care based hierarchical search-line scheme
(2009-04-28)
Chang
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Shu-Wei
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Hwang
;
Wei
;
Chang
In the proposed stored don't-care hierarchical search-line scheme, a content-addressable memory (CAM) is divided into several blocks. Each block contains a plurality of local search-lines, a global search-line, a buffer and a memory memory cell. Data are stored in the blocks in order according to the length of the prefix. Data with the longest prefix is stored at the bottommost, and its don't-care state is used as the control signal of the buffer to control whether to transfer the data on the global search-line to the local search-line or not. The local search-line then transfer the value into the memory cell. There is no complex control circuit and extra storage device needed. Moreover, because the control signal directly comes from the don't-care state, power consumption on search-lines can be effectively reduced with no increase of search delay.
Mediation of chain reactions by propagating radicals during halogenation of H-masked Si(100): Implications for atomic-scale lithography and processing
(2009-04-28)
Ferng, Shyh-Shin
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Wu, Shiao-Ting
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Lin, Deng-Sung
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Chiang, Tai C.
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物理研究所
Scanning tunneling microscopy reveals a free radical-induced surface chain reaction in the chlorination of nanoscale patterns on an otherwise H-passivated (masked) Si (100). While scanning probe methods can be used to pattern active surface regions with single-bond precision, follow-up selective chemical vapor deposition with polyatomic molecules can produce various filling characteristics. On active surface regions, molecular Cl(2) undergoes an atom abstraction reaction in which a Si dangling bond abstracts one atom of the incident Cl(2) molecule while the complementary Cl atom is scattered away from the initial abstraction site either back into the vacuum or to be captured by a second dangling bond and adsorbed there, or to react with a nearby adsorbed H atom to form volatile HCl. In contrast, I(2) undergoes only dissociative adsorption on two immediately neighboring dangling bonds, whereby two I-Si bonds are formed simultaneously upon cleavage of the I(2) bond. The different chemisorption processes of the two model diatomic molecular gases place intrinsic limitations on atomic-scale lithography and processing: Adsorption of Cl(2) results in spillage over the prepatterned regions of active bonds. In contrast, adsorption of I(2) is a pair process and results in under-filling. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3122987]
Net transport due to noise-induced internal reciprocating motion
(2009-04-28)
Makhnovskii, Yurii A.
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Rozenbaum, Viktor M.
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Yang, Dah-Yen
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Lin, Sheng Hsien
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應用化學系
We consider a system of two coupled Brownian particles fluctuating between two states. The fluctuations are produced by both equilibrium thermal and external nonthermal noise, the transition rates depending on the interparticle distance. An externally induced modulation of the transition rates acts on the internal degree of freedom (the interparticle distance) and generates reciprocating motion along this coordinate. The system moves unidirectionally due to rectification of the internal motion by asymmetric friction fluctuations and thus operates as a dimeric motor that converts input energy into net movement. The properties of the motor are primarily determined by the properties of the reciprocating engine, represented by the interparticle distance dynamics. Two main mechanisms are recognized by which the engine operates: energetic and informational. In the physically important cases where only one of the motion-inducing mechanisms is operative, exact solutions can be found for the model with linearly coupled particles. We focus on the informational mechanism, in which thermal noise is involved as a vital component and the reciprocating velocity exhibits a rich behavior as a function of the model parameters. An efficient rectification method for the reciprocating motion is also discussed. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3116790]
Master curves and radial distribution functions for shear dilatancy of liquid n-hexadecane via nonequilibrium molecular dynamics simulations
(2009-04-28)
Tseng, Huan-Chang
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Wu, Jiann-Shing
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Chang, Rong-Yeu
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應用化學系
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Department of Applied Chemistry
Shear dilatancy, a significant nonlinear behavior of nonequilibrium thermodynamics states, has been observed in nonequilibrium molecular dynamics (NEMD) simulations for liquid n-hexadecane fluid under extreme shear conditions. The existence of shear dilatancy is relevant to the relationship between the imposed shear rate (gamma) over dot and the critical shear rate (gamma) over dot(c). Consequently, as (gamma) over dot < (gamma) over dot(c), the intermolecular equilibrium distance of the fluid remains unchanged, while the nonequilibrium state of the fluid approaches equilibrium. In contrast to (gamma) over dot > (gamma) over dot(c), the intermolecular distance is lengthened substantially by strong shear deformation breaking the equilibrium thermodynamic state so that shear dilatancy takes place. Notably, a characteristic shear rate (gamma) over dot(m), which depends on the root mean square molecular velocity and the average free molecular distance, is found in nonequilibrium thermodynamics state curves. Studies of the variations in the intermolecular radial distribution function (RDF) with respect to the shear rate provide a direct measure of the variation in the degree of intermolecular separation. Additionally, the variations of the RDF curve in the microscopic regime are consistent with those of the nonequilibrium thermodynamic state in the macroscopic world. By inspecting the overall shape of the RDF curve, it can be readily corroborated that the fluid of interest exists in the liquid state. More importantly, both primary characteristic values, the equilibrium thermodynamic state variable and a particular shear rate of (gamma) over dot(p), are determined cautiously, with (gamma) over dot(p) depending on the (gamma) over dot(m) value and the square root of pressure. Thereby, the nonequilibrium thermodynamic state curves can be normalized as temperature-, pressure-, and density-invariant master curves, formulated by applying the Cross constitutive equation. Clearly, (gamma) over dot(c) occurs at which a reduced shear rate (gamma) over dot/(gamma) over dot(p) approaches 0.1. Furthermore, the trends in the rates of shear dilatancy in both the constant-pressure and constant-volume NEMD systems under isothermal conditions conform to the cyclic rule of pressure, as a function of density and shear rate. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3123171]
METHOD FOR MODULATING REFRACTIVE INDICES OF OPTICAL FIBER GRATINGS
(2009-04-30)
HSU, Kuei Chu
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Lai, Yin Chieh
The present invention proposes a method for modulating refractive indices of optical fiber gratings, wherein the UV exposure on a least one assigned location of an optical fiber grating is divided into to two UV shots, and the intensities or phases of the two UV shots, which expose the location sequentially, are controlled to make the total exposure intensity of one assigned location maintained at a fixed value, whereby the interference fringes, which are created by a superposition of the two UV shots, have fixed phases and adjustable intensities, and whereby the dc index of the optical fiber grating maintains fixed and the ac index independently adjustable.
Wireless Communication Receiving System and Apparatus and Method for Deciding a Transmitted Signal Corresponding to a Received Signal Thereof
(2009-04-30)
Wu, Wen-Rong
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Wu, Jiun-Ying
A wireless communication receiving system and an apparatus and a method for deciding a transmitted signal corresponding to a received signal thereof are provided. The transmitted signal comprises a plurality of sub-transmitted signals. The system selects at least one of the sub-transmitted signals as a reference signal group, wherein each of a plurality of candidate values of the reference signal group forms a candidate geometric space respectively. The received signal is projected to each of the candidate geometric spaces to generate a projection signal respectively. In each of the candidate geometric space, the corresponding projection signal is quantized to generate a quantized projection signal having a projection distance to the corresponding projection signal. Finally, the transmitted signal is decided according the quantized projection signal and the candidate signal value corresponding to the shortest projection distance.
Method and Apparatus for Deciding a Channel Impulse Response
(2009-04-30)
Wu, Wen-Rong
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Kao, Shiang-Lun
Method and apparatus for deciding a channel impulse response for an OFDM system are provided. First, a channel frequency response is generated by using a plurality of pilot tones of a signal. A channel impulse response is generated by applying the IFFT to the channel frequency response. A plurality of selected channel taps are derived by comparing a plurality of channel taps related to the channel impulse response with a reference threshold. Finally, the channel impulse response is generated by calculating channel impulse respose according to the selected channel taps. This method calculates the channel impulse response in time domain and frequency domain so that the calculation complexity can be reduced, and the system efficiency can be enhanced.
Wireless Communication Systems, Apparatus and Method for Encoding and Decoding a Plurality of Information Bits
(2009-04-30)
Wu, Wen-Rong
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Shen, Shih-Chi
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Lin, Yu-Cheng
Wireless transmitted system and apparatus and method for encoding a plurality of information bits to a plurality of transmitted signals thereof, and wireless received system and apparatus and method for decoding a received signal to a plurality of information bits thereof are provided. The wireless transmitted system encodes a plurality of information bits to a plurality of transmitted signals by two logic operation modules, an interleaving module, and a combination module. The wireless received system decodes a received signal to a plurality of information bits by a division module, two probability generation modules, two status calculation modules, a signal generation module and a combination module.
Prediction of O(2) Dissociation Kinetics on LaMnO(3)-Based Cathode Materials for Solid Oxide Fuel Cells
(2009-04-30)
Choi, YongMan
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Lynch, Matthew E.
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Lin, M. C.
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Liu, Meilin
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應用化學系分子科學碩博班
First-principles and statistical-theory calculations were applied to examine the interactions between oxygen molecules and the (100) surfaces of LaMnO(3) and La(0.5)Sr(0.5)MnO(2.75), one of the most-used cathode materials in solid oxide fuel cells (SOFCs). To predict the rate constants for the interactions between O(2) and LaMnO(3) or La(0.5)Sr(0.5)MnO(2.75), potential energy profiles were constructed using the nudged elastic band (NEB) method. Predicted rate constants for the dissociation of adsorbed oxygen species on LaMnO(3) (lm) and La(0.5)Sr(0.5)MnO(2.75) (lsm) can be expressed as k(diss,lm) = 2.35 x 10(12) exp(-0.50 eV/RT) s(-1) and k(diss,lsm) = 2.15 x 10(12) exp(-0.23 eV/RT) s(-1), respectively, in the temperature range of 873-1273 K at 1 atm. Because the activation energy for oxygen dissociation on La(0.5)Sr(0.5)MnO(2.75) (0.23 eV) is much smaller than that on LaMnO(3) (0.50 eV), oxygen vacancies greatly enhance O(2) dissociation kinetics. The kinetic and mechanistic studies for the interactions at the molecular level are imperative to gaining a fundamental understanding of oxygen reduction kinetics on cathode materials and to providing important insight into the rational design of more catalytically active cathode materials for SOFCs.
Prediction of O-2 Dissociation Kinetics on LaMnO3-Based Cathode Materials for Solid Oxide Fuel Cells
(2009-04-30)
Choi, YongMan
;
Lynch, Matthew E.
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Lin, M. C.
;
Liu, Meilin
;
應用化學系分子科學碩博班
First-principles and statistical-theory calculations were applied to examine the interactions between oxygen molecules and the (100) surfaces of LaMnO3 and La0.5Sr0.5MnO2.75, one of the most-used cathode materials in solid oxide fuel cells (SOFCs). To predict the rate constants for the interactions between O-2 and LaMnO3 or La0.5Sr0.5MnO2.75, potential energy profiles were constructed using the nudged elastic band (NEB) method. Predicted rate constants for the dissociation of adsorbed oxygen species on LaMnO3 (lm) and La0.5Sr0.5MnO2.75 (lsm) can be expressed as k(diss,lm) = 2.35 x 10(12) exp(-0.50 eV/RT) s(-1) and k(diss,lsm) = 2.15 x 10(12) exp(-0.23 eV/RT) s(-1), respectively, in the temperature range of 873-1273 K at 1 atm. Because the activation energy for oxygen dissociation on La0.5Sr0.5MnO2.75 (0.23 eV) is much smaller than that on LaMnO3 (0.50 eV), oxygen vacancies greatly enhance O-2 dissociation kinetics. The kinetic and mechanistic studies for the interactions at the molecular level are imperative to gaining a fundamental understanding of oxygen reduction kinetics on cathode materials and to providing important insight into the rational design of more catalytically active cathode materials for SOFCs.