Browsing by Issue Date, starting with "2013-07-03"

Now showing 1 - 20 of 31199

Tunable insulator-quantum Hall transition in a weakly interacting two-dimensional electron system
(2013-07-03)
Lo, Shun-Tsung
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Wang, Yi-Ting
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Lin, Sheng-Di
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Strasser, Gottfried
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Bird, Jonathan P.
We have performed low-temperature measurements on a gated two-dimensional electron system in which electron-electron (e-e) interactions are insignificant. At low magnetic fields, disorder-driven movement of the crossing of longitudinal and Hall resistivities (rho (xx) and rho (xy)) can be observed. Interestingly, by applying different gate voltages, we demonstrate that such a crossing at rho (xx) similar to rho (xy) can occur at a magnetic field higher, lower, or equal to the temperature-independent point in rho (xx) which corresponds to the direct insulator-quantum Hall transition. We explicitly show that rho (xx) similar to rho (xy) occurs at the inverse of the classical Drude mobility 1/mu (D) rather than the crossing field corresponding to the insulator-quantum Hall transition. Moreover, we show that the background magnetoresistance can affect the transport properties of our device significantly. Thus, we suggest that great care must be taken when calculating the renormalized mobility caused by e-e interactions.
Competing Topological and Kondo Insulator Phases on a Honeycomb Lattice
(2013-07-03)
Feng, Xiao-Yong
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Dai, Jianhui
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Chung, Chung-Hou
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Si, Qimiao
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電子物理學系
We investigate the competition between the spin-orbit interaction of itinerant electrons and their Kondo coupling with local moments densely distributed on the honeycomb lattice. We find that the model at half-filling displays a quantum phase transition between topological and Kondo insulators at a nonzero Kondo coupling. In the Kondo-screened case, tuning the electron concentration can lead to a new topological insulator phase. The results suggest that the heavy-fermion phase diagram contains a new regime with a competition among topological, Kondo-coherent and magnetic states, and that the regime may be especially relevant to Kondo lattice systems with 5d-conduction electrons. Finally, we discuss the implications of our results in the context of the recent experiments on SmB6 implicating the surface states of a topological insulator, as well as the existing experiments on the phase transitions in SmB6 under pressure and in CeNiSn under chemical pressure.
Determining Sample Size With a Given Range of Mean Effects in One-Way Heteroscedastic Analysis of Variance
(2013-07-03)
Shieh, Gwowen
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Jan, Show-Li
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交大名義發表
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管理科學系
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National Chiao Tung University
The authors examined 2 approaches for determining the required sample size of Welch's test for detecting equality of means when the greatest difference between any 2 group means is given. It is shown that the actual power obtained with the sample size of the suggested approach is consistently at least as great as the nominal power. However, the sample size given by the method of Guo and Luh (2008) does not always guarantee the minimum power performance. Furthermore, the computed sample size and associated power of their formula tend to be larger than those provided with the proposed procedure. A supplementary computer program is provided to aid the implementation of the proposed technique in planning analysis of variance designs.
Dynamics of electric transport in interacting Weyl semimetals
(2013-07-03)
Rosenstein, B.
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Lewkowicz, M.
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電子物理學系
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Department of Electrophysics
The response to an electric field (dc and ac) of electronic systems in which the Fermi "surface" consists of a number of three-dimensional (3D) Weyl points (such as some pyrochlore iridates) exhibits a peculiar combination of characteristics usually associated with insulating and conducting behavior. Generically a neutral plasma in clean materials can be described by a tight-binding model with a strong spin-orbit interaction. A system of that type has a vanishing dc conductivity; however the current response to the dc field is very slow: The current decays with time in a powerwise manner, different from an insulator. The ac conductivity, in addition to a finite real part sigma'(Omega) which is linear in frequency, exhibits an imaginary part sigma '' (Omega) that increases logarithmically as a function of the UV cutoff (atomic scale). This leads to a substantial dielectric response like a large dielectric constant at low frequencies. This is in contrast to a two-dimensional (2D) Weyl semimetal-like graphene at a neutrality point where the ac conductivity is purely pseudodissipative. The Coulomb interaction between electrons is long range and sufficiently strong to make a significant impact on transport. The interaction contribution to the ac conductivity is calculated within the tight-binding model. The result for the real part expressed via the renormalized (at frequency (Omega) over bar) Fermi velocity nu is Delta sigma'(Omega) = e(4)Omega/(9 pi(2)(h) over bar nu)[2 log(Omega/ (Omega) over bar)-5].
Device Simulation-Based Multiobjective Evolutionary Algorithm for Process Optimization of Semiconductor Solar Cells
(2013-07-03)
Li, Yiming
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Chen, Yu-Yu
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Chen, Chieh-Yang
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Shen, Cheng-Han
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Cheng, Hui-Wen
This article implements for the first time a numerical semiconductor device simulation-based multiobjective evolutionary algorithm (MOEA) for the characteristic optimization of amorphous silicon thin-film solar cells, based upon a unified optimization framework (UOF). To calculate the device's characteristic, a set of coupled solar cell transport equations consisting of the Poisson equation, the electron-hole current continuity equations, and the photo-generation model is solved numerically. Electrical characteristics, the short-circuited current, the open-circuited voltage, and the conversion efficiency are calculated to analyze the properties of the explored solar cells. The aforementioned device simulation results are used to evaluate the fitness score and access the evolutionary quality of designing parameters via the implemented non-dominating sorting genetic algorithm (NSGA-II) in the UOF. Notably, designing parameters including the material and structural parameters, and the doping concentrations are simultaneously optimized for the explored solar cells. The simulation-based MOEA methodology is useful in optimal structure design and manufacturing of semiconductor solar cells.
CURRENT STIMULATOR
(2013-07-04)
Lin Chun-Yu
;
Li Yi-ju
;
Ker Ming-Dou
The disclosure relates to a current stimulator, which comprises a high voltage output module, a voltage control module and a charge pump module. The high voltage output module includes a plurality of stacked transistors, and receives an input control signal able to turn on/off the current stimulator and a first voltage. A second voltage is generated by adding the voltages output by all the transistors to the first voltage and then output to the voltage control module. The voltage control module outputs a voltage control signal able to stabilize the stimulus current for the load according to the second voltage and the load impedance variation. The charge pump regulates the first voltage according to the voltage control signal, and outputs the regulated first voltage to the high voltage output module. Thereby, the current stimulator can adaptively stabilize the stimulus current, responding to load impedance variation.
METHOD FOR IMPROVING IMAGING RESOLUTION OF ELECTRICAL IMPEDANCE TOMOGRAPHY
(2013-07-04)
Choi Charles Tak Ming
;
Sun Shu-Hai
The present disclosure provides a method for improving imaging resolution of electrical impedance tomography (EIT). More specifically, the present disclosure forms virtual electrode(s) using an electric current steering technique, which is used to improve imaging resolution of an EIT system without physically increasing a number of conducting electrodes. The EIT system of the present disclosure may includes a plurality of conducting electrodes, at least one signal generator, at least one signal receiver and at least one electric current steering device. In other words, the present disclosure applies both the electric current steering technique and the virtual electrode technique to EIT. Consequently, imaging resolution of EIT can be improved without physically increasing the number of conducting electrodes.
Integrated Circuit Device
(2013-07-04)
Chen Kuan-Neng
;
Lai Ming-Fang
;
Chen Hung-Ming
An integrated circuit device includes: a first chip including a first substrate and a main circuit formed on said first chip; a second chip stacked on the first substrate and including a second substrate that is independent from the first substrate, and a protective circuit for protecting the main circuit; and a conductive channel unit extending from the protective circuit and electrically connected to the main circuit.
BIOLOGICAL DETECTION DEVICE AND DETECTING METHOD
(2013-07-04)
LIN Yi-Hsin
;
Chu Wei-Lin
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Wu Li-Ching
The present invention discloses a biological detection device and a detecting method. The biological detection device comprises a substrate, an electric field unit, a liquid crystal/polymer composite film (LCPCF), a power supply, a processing unit, and an image sensor. Because of the electrically tunable orientations of the liquid crystal (LC) director anchored among the polymer grains, the wettability of the LCPCF changes with an applied electric field. As a result, we can manipulate a blood droplet on the LCPCF by a wettability gradient owing to the distribution of LC directors on the LCPCF. The motion states of the blood droplet can be related to the various qualities of the blood, and finally determines the health of the test sample. The change of contact angle of blood on LCPCF and the blood droplet motion on LCPCF indicate the concentration of TG and the concentration of HDL.
Sound Wave Propagation Anisotropy in Silver Nanoprisms: Characterization of Photoinduced Multiple Modes Using the Symmetric Molecular Dynamics Method
(2013-07-04)
Ng, Ming-Yaw
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Yu, Pyng
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Tang, Jau
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Chang, Yia-Chung
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光電工程學系
We present both theoretical and experimental studies of the sound velocity anisotropy and laser-induced multiple acoustic phonon oscillations in silver nanoprisms. A large-scale simulation method based on molecular dynamics and group theory for nanoprisms with C-3v symmetry was developed. We observed the most prominent planar modes and the less studied vertical modes and found that the anisotropic vibrational properties of silver nanoprisms strongly depend on the particle's aspect ratio (bisector length over thickness). For the case of a smaller aspect ratio, we identified these modes as the A, modes with a larger in phase radial atomic displacement These modes can be classified into three main types: breathing modes and totally symmetric modes which are planar modes and thickness-related vertical modes. Due to the strong coupling with laterally confined modes, a broad band of thickness-related modes is found (in contrast to a single sharp peak for thin films), which leads to a fast decaying component in the oscillation spectrum. The calculated results and the sound velocity anisotropy along different crystal axes are in good agreement with our transient optical absorption experiments.
METHOD FOR REMOVING GERMANIUM SUBOXIDE
(2013-07-04)
Liu Po-Tsun
;
Huang Chen-Shuo
A method for removing germanium suboxide between a germanium (Ge) substrate and a dielectric layer made of metal oxide includes causing a supercritical fluid composition that includes a supercritical carbon dioxide fluid and an oxidant to diffuse into the germanium suboxide such that metal residues in the dielectric layer, the germanium suboxide and the oxidant are subjected to a redox reaction so as to reduce the germanium suboxide into germanium.
Realistic quantum design of silicon quantum dot intermediate band solar cells
(2013-07-05)
Hu, Weiguo
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Igarashi, Makoto
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Lee, Ming-Yi
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Li, Yiming
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Samukawa, Seiji
A highly periodical Si nanodisk superlattice has been fabricated by our top-down process. Based on the realistic structure, a 3D simulation program using the finite element method is developed to calculate energy band structure, optical and electrical properties, as well as the intermediate band solar cell operation. Both the experiments and simulations reveal that miniband formation enhances the optical and electrical collections. Consequently, detailed electronic structure and conversion efficiency are examined to guide the optimal design of minibands. A theoretically predicted maximal efficiency of the explored Si nanodisk superlattice is 50.3%, which is promising, compared with well-known complicated Si tandem solar cells.
交大e-News第144期
(2013-07-05)
Secretariat
;
國立交通大學秘書室
Platinum-graphene counter electrodes for dye-sensitized solar cells
(2013-07-07)
Cheng, Cheng-En
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Lin, Chi-Yuan
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Shan, Chien-Hsun
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Tsai, Shang-Yi
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Lin, Ko-Wei
This paper describes the photovoltaic performance of dye-sensitized solar cells (DSSCs) containing graphene-incorporated counter electrodes (CEs). The location and thickness of graphene in CEs are optimized to improve the photovoltaic performance of DSSCs, compared with typical Pt CEs. The DSSC, with a Pt/few-layer graphene (FLG) CE, achieved 8% in short-circuit current density and 13% in power conversion efficiency (PCE). Electrochemical impedance spectroscopy shows that the DSSC, with a Pt/FLG CE, exhibits a series resistance lower than that with a Pt CE. The lower series resistance is attributed to the contact resistance at the interface of platinum and fluorine doped tin oxide. The contact resistance is reduced by the formation of the thin platinum-carbon composite layer. It is demonstrated that the consumption of Pt could be reduced with a Pt/FLG CE. However, graphene/Pt CEs resulted in a slow charge-transfer process and consequently a worse photovoltaic performance of DSSCs. (C) 2013 AIP Publishing LLC.
Abnormal sub-threshold swing degradation under dynamic hot carrier stress in HfO2/TiN n-channel metal-oxide-semiconductor field-effect-transistors
(2013-07-08)
Tsai, Jyun-Yu
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Chang, Ting-Chang
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Lo, Wen-Hung
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Chen, Ching-En
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Ho, Szu-Han
This work finds abnormal sub-threshold swing (S.S.) degradation under dynamic hot carrier stress (HCS) in n-channel metal-oxide-semiconductor field-effect-transistors with high-k gate dielectric. Results indicate that there is no change in S.S. after dynamic HCS due to band-to-band hot hole injection at the drain side which acts to diminish the stress field. Moreover, the impaired stress field causes the interface states to mainly distribute in shallow states. This results in ON state current and transconductance decreases, whereas S.S. degradation is insignificant after dynamic HCS. The proposed model is confirmed by one-side charge pumping measurement and gate-to-drain capacitance at varying frequencies. (C) 2013 AIP Publishing LLC.
Unraveling the origins of electromechanical response in mixed-phase bismuth ferrite
(2013-07-08)
Vasudevan, R. K.
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Okatan, M. B.
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Liu, Y. Y.
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Jesse, S.
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Yang, J. -C.
The origin of giant electromechanical response in a mixed-phase rhombohedral-tetragonal BiFeO3 thin film is probed using subcoercive scanning probe microscopy based multiple-harmonic measurements. Significant contributions to the strain arise from a second-order harmonic response localized at the phase boundaries. Strain and dissipation data, backed by thermodynamic calculations, suggest that the source of the enhanced electromechanical response is the motion of phase boundaries. These findings elucidate the key role of labile phase boundaries, both natural and artificial, in achieving thin films with giant electromechanical properties.
Adiabatically driven Brownian pumps
(2013-07-08)
Rozenbaum, Viktor M.
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Makhnovskii, Yurii A.
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Shapochkina, Irina V.
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Sheu, Sheh-Yi
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Yang, Dah-Yen
We investigate a Brownian pump which, being powered by a flashing ratchet mechanism, produces net particle transport through a membrane. The extension of the Parrondo's approach developed for reversible Brownian motors [Parrondo, Phys. Rev. E 57, 7297 (1998)] to adiabatically driven pumps is given. We demonstrate that the pumping mechanism becomes especially efficient when the time variation of the potential occurs adiabatically fast or adiabatically slow, in perfect analogy with adiabatically driven Brownian motors which exhibit high efficiency [Rozenbaum et al., Phys. Rev. E 85, 041116 (2012)]. At the same time, the efficiency of the pumping mechanism is shown to be less than that of Brownian motors due to fluctuations of the number of particles in the membrane.
Self-assembly of hierarchical MoSx/CNT nanocomposites (2 < x < 3): towards high performance anode materials for lithium ion batteries
(2013-07-09)
Shi, Yumeng
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Wang, Ye
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Wong, Jen It
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Tan, Alex Yuan Sheng
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Hsu, Chang-Lung
Two dimension (2D) layered molybdenum disulfide (MoS2) has emerged as a promising candidate for the anode material in lithium ion batteries (LIBs). Herein, 2D MoSx (2 <= x <= 3) nanosheet-coated 1D multiwall carbon nanotubes (MWNTs) nanocomposites with hierarchical architecture were synthesized via a high-throughput solvent thermal method under low temperature at 2006 degrees C. The unique hierarchical nanostructures with MWNTs backbone and nanosheets of MoSx have significantly promoted the electrode performance in LIBs. Every single MoSx nanosheet interconnect to MWNTs centers with maximized exposed electrochemical active sites, which significantly enhance ion diffusion efficiency and accommodate volume expansion during the electrochemical reaction. A remarkably high specific capacity (i.e., >1000 mAh/g) was achieved at the current density of 50 mA g(-1), which is much higher than theoretical numbers for either MWNTs or MoS2 along (similar to 372 and similar to 670 mAh/g, respectively). We anticipate 2D nanosheets/1D MWNTs nanocomposites will be promising materials in new generation practical LIBs.
Flexible micro-system and fabrication method thereof
(2013-07-09)
Chao Tzu-Yuan
;
Liang Chia-Wei
;
Cheng Yu-Ting
A fabrication method for integrating chip(s) onto a flexible substrate in forming a flexible micro-system. The method includes a low-temperature flip-chip and a wafer-level fabrication process. Using the low-temperature flip-chip technique, the chip is bonded metallically onto the flexible substrate. To separate the flexible substrate from the substrate, etching is used to remove the sacrificial layer underneath the flexible substrate. The instant disclosure applies standardized micro-fabrication process for integrating chip(s) onto the flexible substrate. Without using special materials or fabrication procedures, the instant disclosure offers a cost-effective fabrication method for flexible micro-systems.
Wetted wall venturi scrubber with a 2-stage venturi throat
(2013-07-09)
Tsai Chuen-Jinn
A venturi scrubber which avoids clogging in the throat by dust particles is developed. The scrubber includes a venturi tube, two scrubbing fluid conduits and a storage tank. The venturi tube has a converging section, a diverging section and a throat section which is connected between the converging section and the diverging section. The scrubbing fluid conduit has a top end connected with the bottom end of the converging section of the venturi tube, and a bottom end extending into the storage tank. Thereby, scrubbing fluid can be guided directly into the storage tank without passing through the throat section. As a result, the clogging of dust particles on the converging section of the venturi throat can be minimized and the abnormal increase in the pressure drop of the air flow through the throat can also be avoided.