Browsing by Issue Date, starting with "2010-10-21"

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Interplay of Spinodal and Diffusion-Limited Aggregation in Formation of Nanocrystal Assembled 2D Islands
(2010-10-21)
Ou, Yi-Ching
;
Zhuravelv, Konstantin S.
;
Fang, Jiye
;
Jian, Wen-Bin
;
電子物理學系
Although self-organization of semiconductor nanocrystals (or quantum dots) into 3D superlattices and exploration of their collective optical, magnetic, and transport properties have been (demonstrated. little is known about the underlying physics of self-assembly, growth mechanisms, and interdot-coupling-induced collective properties. Here we report a facile way of preparing nanocrystal-assembled 2D islands by dropcasting nanocrystal suspension on a hot substrate. Growth mechanisms such as scaling function, spinodal decomposition phase separation, and diffusion-limited aggregation are investigated based on the observation of quasi-monolayer coverage. After a curve fitting to several theoretical growth models, the pair bond (interaction) energy, critical nucleus size, and the phase of growth patterns were determined. Moreover, by heating the substrate and controlling the concentration of nanocrystal suspension, the spinodal decomposition and diffusion-limited aggregation can be tuned to modulate growth patterns of 2D nanocrystal islands. The interplay of these two mechanisms results in a variation or wavelength in spinodal growth patterns and of fractal pattern dimensions. By using this experimental approach. various sizes and shapes of nanocrystal-assembled 2D islands can be deposited on a flat surface of either graphite or gold.
Pressure-dependent electronic structures in multiferroic DyMnO(3): A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
(2010-10-21)
Chen, J. M.
;
Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
;
Huang, S. W.
Variations in the electronic structure and structural distortion in multiferroic DyMnO(3) were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO(6) octahedra in DyMnO(3) on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO(3) progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO(3) shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO(6) octahedra in compressed DyMnO(3). A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490400]
Theoretical Interpretation of the UV-vis Spectrum of the CS(2)/Cl Complex in the Spectral Region 320-550 nm
(2010-10-21)
Camacho, Cristopher
;
Cheng, Chi-Wen
;
Witek, Henryk A.
;
Lee, Yuan-Pern
;
應用化學系
Accurate multireference configuration interaction and time-dependent density functional calculations have been performed to interpret the experimental UV-vis spectrum of the CS(2)/Cl complex in the spectral region 320-550 nm. The molecular structure of the complex responsible for the previously observed UV-vis spectrum is recognized as ClSCS, not CICS(2). Two low-lying excited states of ClSCS, responsible for its optical absorption, have been identified and analyzed. Optical excitation of ClSCS leads to the excitation-specific bond elongation that may lead to photofragmentation of the molecule. In addition, experimental conditions for verifying the presence of ClCS(2) are identified and detailed characterization of its optically active excited states with possible photofragmentation pathways is given.
Pressure-dependent electronic structures in multiferroic DyMnO3: A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
(2010-10-21)
Chen, J. M.
;
Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
;
Huang, S. W.
Variations in the electronic structure and structural distortion in multiferroic DyMnO3 were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO6 octahedra in DyMnO3 on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO3 progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO3 shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO6 octahedra in compressed DyMnO3. A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490400]
Theoretical Interpretation of the UV-vis Spectrum of the CS2/Cl Complex in the Spectral Region 320-550 nm
(2010-10-21)
Camacho, Cristopher
;
Cheng, Chi-Wen
;
Witek, Henryk A.
;
Lee, Yuan-Pern
;
應用化學系
Accurate multireference configuration interaction and time-dependent density functional calculations have been performed to interpret the experimental UV-vis spectrum of the CS2/Cl complex in the spectral region 320-550 nm. The molecular structure of the complex responsible for the previously observed UV-vis spectrum is recognized as ClSCS, not CICS2. Two low-lying excited states of ClSCS, responsible for its optical absorption, have been identified and analyzed. Optical excitation of ClSCS leads to the excitation-specific bond elongation that may lead to photofragmentation of the molecule. In addition, experimental conditions for verifying the presence of ClCS2 are identified and detailed characterization of its optically active excited states with possible photofragmentation pathways is given.
Characteristics of AgInSbTe-SiO2 nanocomposite thin film applied to nonvolatile floating gate memory devices
(2010-10-22)
Chiang, Kuo-Chang
;
Hsieh, Tsung-Eong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Nanocomposite thin films containing AgInSbTe (AIST) particles embedded in an SiO2 matrix was prepared by sputtering deposition and its feasibility for nonvolatile floating gate memory (NFGM) was investigated. The sample subjected to a 400 degrees C annealing exhibited a distinct hysteresis memory window (Delta V-FB) shift = 6.6 V and charge density = 5.2 x 10(12) cm(-2) after +/- 8 V gate voltage sweep. Electrical measurement revealed the current transport is via the Schottky emission in low applied field and the space-charge-limited conduction mechanism in high applied field in the samples, regardless of their thermal history. Transmission electron microscopy and x-ray photoelectron spectroscopy indicated that the metallic Sb2Te nanocrystals (NCs) with diameters about 5-7 nm dispersed in a nanocomposite layer may serve as the discrete charge-storage traps for nonvolatile memory. Analytical results illustrate the utilization of an AIST-SiO2 nanocomposite layer as the core structure of NFGM devices is able to simplify the device structure and fabrication process.
Quasi-two-dimensional d-spin and p-hole ordering in the three-dimensional perovskite La1/3Sr2/3FeO3
(2010-10-22)
Okamoto, J.
;
Huang, D. J.
;
Chao, K. S.
;
Huang, S. W.
;
Hsu, C. -H.
Measurements of resonant soft x-ray magnetic scattering reveal anomalous ordering of 3d spins and 2p holes in perovskite La1/3Sr2/3FeO3, which is known to exhibit three-dimensional (3D) charge and spin ordering along the (111) direction. Upon cooling, a quasi-two-dimensional phase consisting of ferromagnetic and charge-disproportionated [111] trilayers of Fe3+-Fe5+-Fe3+ precedes the development of 3D magnetic ordering at the transition temperature, in sharp contrast to an ordinary transition from the paramagnetic and charge-uniform phase to the antiferromagnetic and charge-disproportionated phase expected according to conventional wisdom.
An Organic Hole Transport Layer Enhances the Performance of Colloidal PbSe Quantum Dot Photovoltaic Devices
(2010-10-22)
Kuo, Chih-Yin
;
Su, Ming-Shin
;
Hsu, Yu-Chien
;
Lin, Hui-Ni
;
Wei, Kung-Hwa
A thin poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole transport layer enhances the AM1.5 power conversion efficiency of a PbSe quantum dot (QD)-containing photovoltaic device to 2.4%, from 1.5% for a standard PbSe QD device, a relative increase of 60%. Synchrotron X-ray reflectivity measurements reveal that the roughness of the interfaces between the various layers decreases dramatically in the presence of the PEDOT: PSS layer. In addition, the device life time under continuous simulated AM1.5 irradiation (100 mW cm(-2)), measured in terms of the time required to reach 80% of the normalized efficiency, for the PbSe QD device incorporating the PEDOT:PSS hole transport layer is six times longer than that of the standard PbSe QD device.
Characteristics of AgInSbTe-SiO(2) nanocomposite thin film applied to nonvolatile floating gate memory devices
(2010-10-22)
Chiang, Kuo-Chang
;
Hsieh, Tsung-Eong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Nanocomposite thin films containing AgInSbTe (AIST) particles embedded in an SiO(2) matrix was prepared by sputtering deposition and its feasibility for nonvolatile floating gate memory (NFGM) was investigated. The sample subjected to a 400 degrees C annealing exhibited a distinct hysteresis memory window (Delta V(FB)) shift = 6.6 V and charge density = 5.2 x 10(12) cm(-2) after +/- 8 V gate voltage sweep. Electrical measurement revealed the current transport is via the Schottky emission in low applied field and the space-charge-limited conduction mechanism in high applied field in the samples, regardless of their thermal history. Transmission electron microscopy and x-ray photoelectron spectroscopy indicated that the metallic Sb(2)Te nanocrystals (NCs) with diameters about 5-7 nm dispersed in a nanocomposite layer may serve as the discrete charge-storage traps for nonvolatile memory. Analytical results illustrate the utilization of an AIST-SiO(2) nanocomposite layer as the core structure of NFGM devices is able to simplify the device structure and fabrication process.
Probing the sensitivity of nanowire-based biosensors using liquid-gating
(2010-10-22)
Lu, Ming-Pei
;
Hsiao, Cheng-Yun
;
Lai, Wen-Tsan
;
Yang, Yuh-Shyong
;
生物科技學系
We have used liquid-gating to investigate the sensitivity of nanowire (NW)-based biosensors for application in the field of ultrasensitive biodetection. We developed an equivalent capacitance model of the biosensor system to explore the dependence of the sensitivity on the liquid-gate voltage (V(lg)), which was influenced by capacitive competition between the NW capacitance and the thin oxide capacitance. NW biosensors with highest sensitivity were obtained when we operated the device in the subthreshold regime while applying an appropriate value of Vlg; the influence of leakage paths through the ionic solutions led, however, to significant sensitivity degradation and narrowed the operating window in the subthreshold regime.
An Organic Hole Transport Layer Enhances the Performance of Colloidal PbSe Quantum Dot Photovoltaic Devices
(2010-10-22)
Kuo, Chih-Yin
;
Su, Ming-Shin
;
Hsu, Yu-Chien
;
Lin, Hui-Ni
;
Wei, Kung-Hwa
A thin poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hole transport layer enhances the AM1.5 power conversion efficiency of a PbSe quantum dot (QD)-containing photovoltaic device to 2.4%, from 1.5% for a standard PbSe QD device, a relative increase of 60%. Synchrotron X-ray reflectivity measurements reveal that the roughness of the interfaces between the various layers decreases dramatically in the presence of the PEDOT: PSS layer. In addition, the device life time under continuous simulated AM1.5 irradiation (100 mW cm(-2)), measured in terms of the time required to reach 80% of the normalized efficiency, for the PbSe QD device incorporating the PEDOT:PSS hole transport layer is six times longer than that of the standard PbSe QD device.
Direct Observation of Capacitor Switching Using Planar Electrodes
(2010-10-22)
Balke, Nina
;
Gajek, Martin
;
Tagantsev, Alexander K.
;
Martin, Lane W.
;
Chu, Ying-Hao
Ferroelectric polarization switching in epitaxial (110) BiFeO(3) films is studied using piezoresponse force microscopy of a model in-plane capacitor structure. The electrode orientation is chosen such that only two active domain variants exist. Studies of the kinetics of domain evolution allows clear visualization of nucleation sites, as well as forward and lateral growth stages of domain formation. It is found that the location of the reverse-domain nucleation is correlated with the direction of switching in a way that the polarization in the domains nucleated at an electrode is always directed away from it. The role of interface charge injection and surface screening charge on switching mechanisms is explored, and the nucleation is shown to be controllable by the bias history of the sample. Finally, the manipulation of domain nucleation through domain structure engineering is illustrated. These studies pave the way for the engineering and design of the ferroelectric device structures through control of individual steps of the switching process.
Quasi-two-dimensional d-spin and p-hole ordering in the three-dimensional perovskite La(1/3)Sr(2/3)FeO(3)
(2010-10-22)
Okamoto, J.
;
Huang, D. J.
;
Chao, K. S.
;
Huang, S. W.
;
Hsu, C. -H.
Measurements of resonant soft x-ray magnetic scattering reveal anomalous ordering of 3d spins and 2p holes in perovskite La(1/3)Sr(2/3)FeO(3), which is known to exhibit three-dimensional (3D) charge and spin ordering along the (111) direction. Upon cooling, a quasi-two-dimensional phase consisting of ferromagnetic and charge-disproportionated [111] trilayers of Fe(3+)-Fe(5+)-Fe(3+) precedes the development of 3D magnetic ordering at the transition temperature, in sharp contrast to an ordinary transition from the paramagnetic and charge-uniform phase to the antiferromagnetic and charge-disproportionated phase expected according to conventional wisdom.
An analytical solution for tidal fluctuations in unconfined aquifers with a vertical beach
(2010-10-22)
Yeh, H. D.
;
Huang, C. S.
;
Chang, Y. C.
;
Jeng, D. S.
;
環境工程研究所
The perturbation technique has been commonly used to develop analytical solutions for simulating the dynamic response of tidal fluctuations in unconfined aquifers. However, the solutions obtained from the perturbation method might result in poor accuracy for the case of the perturbation parameter being not small enough. In this paper, we develop a new analytical model for describing the water table fluctuations in unconfined aquifers, based on Laplace and Fourier transforms. In the new approach, the mean sea level is used as the initial condition and a free surface equation, neglecting the second-order slope terms, as the upper boundary condition. Numerical results show that the present solution agrees well with the finite different model with the second-order surface terms. Unlike Teo et al.'s (2003) approximation which restricts on the case of shallow aquifers, the present model can be applied to most of the tidal aquifers except for the very shallow one. In addition, a large-time solution in terms of sine function is provided and examined graphically with four different tidal periods.
Mechanical properties of the hexagonal HoMnO3 thin films by nanoindentation
(2010-10-22)
Yen, Cheng-Yo
;
Jian, Sheng-Rui
;
Lai, Yi-Shao
;
Yang, Ping-Feng
;
Liao, Ying-Yen
The structural and nanomechanical characteristics of the hexagonal HoMnO3 (HMO) thin films are investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation techniques in this study. The HMO thin films were deposited on YSZ(1 1 1) substrates by pulsed laser deposition (PLD). The XRD results reveal only pure (0 0 0 1)-oriented hexagonal HMO reflections without any discernible traces of impurity or secondary phases. Nanoindentation results exhibit discontinuities in the load-displacement curve (so-called multiple "pop-ins" event) during loading, indicating possible involvement of dislocation activities. No discontinuities were observed on unloading segment of the load-displacement curve. Continuous stiffness measurements (CSM) technique was carried out in the nanoindentation tests to determine the hardness and Young's modulus of the hexagonal HMO thin films. The obtained hardness and Young's modulus of the hexagonal HMO thin films are 14.2 +/- 0.7 GPa and 219.2 +/- 10.6 GPa, respectively with the room-temperature fracture toughness being in the order of 0.4 +/- 0.2 MPa m(1/2). (c) 2010 Elsevier B.V. All rights reserved.
Mechanical properties of the hexagonal HoMnO(3) thin films by nanoindentation
(2010-10-22)
Yen, Cheng-Yo
;
Jian, Sheng-Rui
;
Lai, Yi-Shao
;
Yang, Ping-Feng
;
Liao, Ying-Yen
The structural and nanomechanical characteristics of the hexagonal HoMnO(3) (HMO) thin films are investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation techniques in this study. The HMO thin films were deposited on YSZ(1 1 1) substrates by pulsed laser deposition (PLD). The XRD results reveal only pure (0 0 0 1)-oriented hexagonal HMO reflections without any discernible traces of impurity or secondary phases. Nanoindentation results exhibit discontinuities in the load-displacement curve (so-called multiple "pop-ins" event) during loading, indicating possible involvement of dislocation activities. No discontinuities were observed on unloading segment of the load-displacement curve. Continuous stiffness measurements (CSM) technique was carried out in the nanoindentation tests to determine the hardness and Young's modulus of the hexagonal HMO thin films. The obtained hardness and Young's modulus of the hexagonal HMO thin films are 14.2 +/- 0.7 GPa and 219.2 +/- 10.6 GPa, respectively with the room-temperature fracture toughness being in the order of 0.4 +/- 0.2 MPa m(1/2). (c) 2010 Elsevier B.V. All rights reserved.
光明的路
(2010-10-24)
張瑜庭
;
Department of Communication and Technology
;
傳播與科技學系
「叩、叩……」熟睡中，我隱約聽到沈重的敲擊聲，「吵死了！我還想睡噎！」我喊道，但是沒有人理我。
超越自我一念之間
(2010-10-24)
周揚珊
;
Department of Communication and Technology
;
傳播與科技學系
「出去！」教練以震耳欲聾的聲音對我咆哮著，我，動彈不得，傻愣地杵在原地。一股幾近昏厥的窒息感迎面而來，在黑暗中，我想起幼稚園時溺水的那一天。
不只拜金名牌戀人
(2010-10-24)
劉怡潔
;
Department of Communication and Technology
;
傳播與科技學系
芙珞．戴珊妮是個詐騙界的藝術家，整套的設計師精品黑色套裝，襯托出芙珞出色的外貌。她總是帶著這些武器出席富裕多金、心碎哀戚的獨身巨賈為亡妻舉辦的喪禮，及時提供他們一個可以依靠的肩膀，在芙珞成功取得信任之後，便挪用現金，無情的一走了之，繼續下一個「喪偶富翁淘金計劃」。
全民反毒無毒有我
(2010-10-24)
黃萱如
;
Department of Communication and Technology
;
傳播與科技學系
慈濟功德會舉辦「無毒有我全民反毒」校園巡迴特映會，十月十七日來到交通大學，這個特映會是由交大慈青社和慈濟聯合舉辦，活動主題是放映「逆子」這部片，以男主角的心路歷程告知參與的大眾，毒千萬碰不得。而除了影片欣賞，慈濟也進行拒毒的手語教學，這場特映會有非常多的民眾一家大小來參與，想必能給參與的人帶來不少的收穫。