Browsing by Author "Lin, J. J."

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Cross-sectional shape modulation of physical properties in ZnO and Zn(1-x)Co(x)O nanowires
(2008-03-12)
Wu, Z. Y.
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Chen, I. J.
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Lin, Y. F.
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Chiu, S. P.
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Chen, F. R.
We have prepared comparable-diameter ZnO and Zn(1-x)Co(x)O nanowires with both circular and hexagonal cross-sections. The average diameters are similar to 113 and similar to 134 nm for cylindrical and hexagonal nanowires, respectively. The as-grown nanowires have been characterized via structure, electrical conductivity and photoluminescence (PL) spectrum measurements. Pure ZnO nanowires were Co-ion implanted to make magnetic Zn(1-x)Co(x)O nanowires for magnetization studies. Bumpier edge surfaces on a nanometre scale, higher densities of stacking faults and a bending feature along the growth direction have been found in cylindrical ZnO nanowires. As compared with hexagonal nanowires, we have observed relatively higher conductivities in cylindrical nanowires, which implied large numbers of shallow donors existing in the latter nanowires. The cylindrical ZnO nanowires also displayed intensified green defect emission and considerably more stacking faults in the crystalline structure. In addition, we have found increased magnetization and stronger ferromagnetic ordering in cylindrical than in hexagonal Zn(1-x)Co(x)O nanowires, and have experimentally identified that the point defects of either Zn interstitials or O vacancies played governing roles in ferromagnetism. We conclude that the cross-sectional shape effect originating a varied point defect density can profoundly modulate the structural, electrical, optical as well as magnetic properties of ZnO and Zn(1-x)Co(x)O nanowires.
Determination of contact and intrinsic nanowire resistivity in two-contact ZnO nanowire devices
(2008)
Lin, Y. F.
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Jian, W. B.
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Wu, Z. Y.
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Chen, F. R.
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Kai, J. J.
Cylindrical ZnO nanowires were synthesized to fabricate two-contact ZnO nanowire devices with the same separation distance between the two contact electrodes. Electrical properties including temperature dependence of resistance and I-V curves were recorded. According to distinct electrical behaviors and room-temperatare resistance, ZnO nanowire devices can be categorized into three different types exhibiting either contact or intrinsic NW attributes.
Electrical measurements on iridium dioxide nanorods
(2006)
Lin, Y. H.
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Lee, T. C.
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Lin, J. J.
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Chang, H. M.
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Huang, Y. S.
Iridium dioxide (IrO2) nanorods have been prepared by metal-organic chemical vapor deposition method. Applying the standard electron-beam lithography technique, a single nanorod with a diameter of I 10 nm is contacted by three Cr/Au fingers from above. The resistance measurements on this nanorod have been performed between 10 and 300 K, using different probe configurations. We observe that the resistivity rho of the nanorod has a value <= 120 mu Omega cm at 300 K. On the other hand, the temperature dependence of the contact resistance R obeys the law logR proportional to T-1/2 below 100 K. The conduction process through the contact is ascribed to the transport of electrons via hopping in granular metals accidentally formed at the contact region.
Electrical transport in transparent conducting tin-doped indium oxide films
(2006)
Yeh, S. S.
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Lu, J. Y.
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Shiu, M. W.
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Lin, J. J.
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物理研究所
We have studied the temperature behavior of the electrical resistivities rho(T) in a series of tin-doped indium-oxide films with different residual resistivities rho(0) varying from 218 to 568 mu Omega cm. We found that the temperature dependence of p can be well described by the Bloch-Gruneisen law from 300 K down to about 100 K. In particular, we observed that the strength of the electron-phonon coupling, beta(BG), (which characterizes a prefactor in the Bloch-Gruneisen formula) increases linearly with increasing rho(0). This result is not understood in terms of current theoretical concept for electron-phonon interaction in metals.
Electrical transport studies of individual IrO(2) nanorods and their nanorod contacts
(2008-01-30)
Lin, Y. H.
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Sun, Y. C.
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Jian, W. B.
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Chang, H. M.
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Huang, Y. S.
We have studied the electrical transport properties of individual single-crystalline IrO(2) nanorods prepared by the metal-organic chemical vapour deposition method. With the help of the standard electron-beam lithographic technique, individual nanorods are contacted by Cr/Au submicron electrodes from above. Utilizing two-probe, three-probe and four-probe measurement configurations, not only the intrinsic electrical transport properties of the individual nanorods but also the electronic contact resistances, Rc(T), have been determined from 300 K down to liquid-helium temperatures. Our measured resistivity behaviour of the nanorods is in close agreement with the current theoretical understanding of this rutile material. On the other hand, we found that the temperature behaviour of the electronic contact resistance obeys the law log R(C) alpha T(-1/2) over an extremely wide temperature range, from approximately 100 K down to liquid-helium temperatures. This latter conduction process is ascribed to the hopping of electrons through nanoscale Cr granules and/or an amorphous coating incidentally formed at the interface between the submicron Cr/Au electrode and the nanorod.
Electrical transport studies of individual IrO2 nanorods and their nanorod contacts
(2008-01-30)
Lin, Y. H.
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Sun, Y. C.
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Jian, W. B.
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Chang, H. M.
;
Huang, Y. S.
We have studied the electrical transport properties of individual single-crystalline IrO2 nanorods prepared by the metal-organic chemical vapour deposition method. With the help of the standard electron-beam lithographic technique, individual nanorods are contacted by Cr/Au submicron electrodes from above. Utilizing two-probe, three-probe and four-probe measurement configurations, not only the intrinsic electrical transport properties of the individual nanorods but also the electronic contact resistances, Rc(T), have been determined from 300 K down to liquid-helium temperatures. Our measured resistivity behaviour of the nanorods is in close agreement with the current theoretical understanding of this rutile material. On the other hand, we found that the temperature behaviour of the electronic contact resistance obeys the law log R-C alpha T-1/2 over an extremely wide temperature range, from approximately 100 K down to liquid-helium temperatures. This latter conduction process is ascribed to the hopping of electrons through nanoscale Cr granules and/or an amorphous coating incidentally formed at the interface between the submicron Cr/Au electrode and the nanorod.
Electron dephasing near zero temperature: an experimental review
(2003-02-01)
Lin, J. J.
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Li, T. J.
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Zhong, Y. L.
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電子物理學系
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物理研究所
The behavior of the electron dephasing time near zero temperature, tau(0)(phi), has recently attracted vigorous attention. This renewed interest is primarily concerned with whether tau(0)(phi) should reach a finite or an infinite value as T -> 0. While it is accepted that tau(0)(phi) should diverge if there exists only electron-electron (electron-phonon) scattering, several recent measurements have found that tau(0)(phi) depends only very weakly on temperature, if at all, when T is sufficiently low. This article discusses the current experimental status of "the saturation problem", and concludes that the origin(s) for this widely observed saturation are still unresolved.
Electron-electron scattering in three-dimensional highly degenerate semiconductors
(2013-08-01)
Zhang, Y. J.
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Li, Z. Q.
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Lin, J. J.
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電子物理學系
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物理研究所
We have measured the low-field magnetoresistances of a series of Sn-doped indium oxide thick films in the temperature T range of 4-35 K. The electron dephasing rate 1/t. as a function of T for each film was extracted by comparing the magnetoresistance data with the threedimensional weak-localization theoretical predictions. We found that the extracted 1/t. varies linearly with T-3/2. Furthermore, at a given T, 1/t. varies linearly with k(F)(-5/2) F l(-3/2), where kF is the Fermi wave number, and l is the electron elastic mean free path. These features are well explained in terms of the small-energy-transfer electron-electron scattering time in three-dimensional disordered conductors. This electron dephasing mechanism dominates over the electron-phonon scattering process because the carrier concentrations in our films are similar to 3 orders of magnitude lower than those in typical metals, which resulted in a greatly suppressed electron-phonon relaxation rate. Our result is the first quantitative demonstration of this unique three-dimensional electron-electron scattering time in experiments. Copyright (C) EPLA, 2013
Electron-phonon dephasing time due to the quasistatic scattering potential in metallic glass CuZrAl
(2006-11-01)
Li, L.
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Lin, S. T.
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Dong, C.
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Lin, J. J.
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電子物理學系
We have measured the electron-phonon scattering time in the metallic glass CuZrAl between 0.37 and 16 K, using the weak-localization magnetoresistance. The electron dephasing rate reveals a T-2 temperature dependence for almost two decades of temperature and is in good quantitative agreement with the theory considering the interference of electron-phonon and elastic electron scattering mechanisms in the presence of quasielastic scattering potential. In addition, this result demonstrates that the Pippard ineffectiveness condition for electron-phonon scattering is not applicable to amorphous alloys that comprise atoms with considerably different atomic masses.
Fabrication and low temperature thermoelectric properties of NaxCoO2 (x=0.68 and 0.75) epitaxial films by the reactive solid-phase epitaxy
(2007-02-05)
Chang, W. J.
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Hsieh, C. C.
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Chung, T. Y.
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Hsu, S. Y.
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Wu, K. H.
The authors have fabricated NaxCoO2 thin films via lateral diffusion of sodium into Co3O4 (111) epitaxial films (reactive solid-phase epitaxy [Ohta , Cryst. Growth Des. 5, 25 (2005)]). The environment of thermal diffusion is key to the control of the sodium content in thin films. From the results of x-ray diffraction and in-plane rho(ab), the epitaxial growth and the sodium contents of these films were identified. The thermoelectric measurements show a large thermoelectric power similar to that observed in single crystals. The quasiparticle scattering rate is found to approach zero at low temperatures, consistent with the small residual resistivity, indicating high quality of the NaxCoO2 thin films. (c) 2007 American Institute of Physics.
Fabrication, characterization and studies of annealing effects on ferromagnetism in Zn1-xCoxO nanowires
(2006-11-14)
Wu, Z. Y.
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Chen, F. R.
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Kai, J. J.
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Jian, W. B.
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Lin, J. J.
Diluted magnetic semiconductor Zn1-xCoxO ( x <= 0.11) nanowires with average diameter of similar to 40 nm were prepared by thermal evaporation, followed by high-energy Co ion implantation. Bombardment by Co ions produced a good number of structural defects (stacking faults and orientational variations) in the nanowires. The as-implanted nanowires were paramagnetic. We performed two types of thermal annealing, one in 1 atm argon flow and the other in a high vacuum, at 600 degrees C, and studied the effects of annealing on the magnetic properties of these nanowires. Argon annealing removed structural defects in the nanowires and the nanowires then revealed ferromagnetic ordering. This result suggests that structure defects are harmful to the occurrence of ferromagnetism in the Co- implanted ZnO. The structure of the as-implanted and the annealed nanowires was inspected in detail by using scanning electron microscopy, energy dispersive x-ray spectroscopy, maps of electron energy loss spectra, x-ray diffraction, and high-resolution transmission electron microscopy. Taken together, these studies suggested that no second phase existed on the scale down to the spatial resolution of similar to 0.5 nm. Noticeably, the nanowires even displayed largely enhanced ferromagnetism after annealing in a high vacuum. A subsequent annealing in oxygen has also been performed on those vacuum-annealed nanowires to study the roles played by the O vacancies in determining the ferromagnetic properties of the nanowires. Our results indicate that both the improved structural quality and the increased number of O vacancies are key factors for the occurrence of ferromagnetic ordering in the Zn1-xCoxO nanowires.
Local development impact assessment for a high speed rail system: a Taiwan study
(2008-01-01)
Lin, J. J.
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Feng, C. M.
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Huang, L. C.
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運輸與物流管理系註：原交通所+運管所
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Department of Transportation and Logistics Management
The Taiwan high speed rail (HSR) system has been in commercial operation since January 2007. Based on the experience of previous freeway development in the area, HSR has the potential to significantly influence local development in western Taiwan. This study focused on the impact of the Taiwan HSR system on local development. Simultaneous equation modeling was applied to analyze the associations among development sectors, and is calibrated using samples of 323 villages, towns or cities in Taiwan. The calibrated model is used as a basis for analyzing and discussing the influences of improving accessibility, increasing land supply for urban development, and various other strategies related to the HSR system. This work reached the following conclusions: improving accessibility and increasing urban development land supply influences local population and employment distributions; improving connections between HSR stations and the central city benefits the development of the central city rather than HSR station area; improving connections between HSR stations and individual districts within the metropolitan area increases the HSR service area and balances development among districts, and promoting station area development projects contributes significantly to local development.
Low-temperature electron dephasing time in AuPd revisited
(2007-10-01)
Lin, J. J.
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Lee, T. C.
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Wang, S. W.
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電子物理學系
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物理研究所
Ever since the first discoveries of the quantum-interference transport in mesoscopic systems, the electron dephasing times, T(P, in the concentrated AuPd alloys have been extensively measured. The samples were made from different sources with different compositions, prepared by different deposition methods, and various geometries (ID narrow wires, 2D thin films, and 3D thick films) were studied. Surprisingly, the low-temperature behavior of tau(phi) inferred by different groups over two decades reveals a systematic correlation with the level of disorder of the sample. At low temperatures, where tau(max)(phi) proportional to D-alpha is (nearly) independent of temperature, a scaling T-phi(max) proportional to D-alpha is found, where T-phi(max) is the maximum value of T-phi measured in the experiment, D is the electron diffusion constant, and the exponent alpha is close to or slightly larger than 1. We address this nontrivial scaling behavior and suggest that the most possible origin for this unusual dephasing is due to dynamical structure defects, while other theoretical explanations may not be totally ruled out. (c) 2007 Elsevier B.V. All rights reserved.
Magnetoresistance and percolation in Au-p-(PrBa2Cu3O7)(1-p) composites
(2006-10-18)
Le Touze, C.
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Lin, J. J.
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電子物理學系
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物理研究所
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Department of Electrophysics
We examine the transverse magnetoresistance of three-dimensional bicomponent composites Au-p-(PrBa2Cu3O7)(1-p). This property, seldom measured on percolation systems, has been measured below 5 K and up to 1.5 T. Contrarily to well known transport properties, the magnetoresistance of these compounds exhibits a metal volume fraction's threshold pc linked to the onset of disorder rather than to percolation.
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.
Spin blockade with spin singlet electrons
(2012-12-24)
Sun, Y. C.
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Amaha, S.
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Huang, S. M.
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Lin, J. J.
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Kono, K.
We observe a singlet spin blockade (SSB) in two-electron vertical double quantum dots where the single-electron transport is blocked for spin singlet electrons. In contrast to the conventional Pauli spin blockade with spin triplet electrons, this singlet spin blockade is observed under high magnetic field, where the doubly occupied states in one of the dots go beyond the singlet-triplet ground-state transition. The SSB region in Coulomb diamond measurements is in agreement with the two-electron excitation spectrum. A leakage current of 10 pA order is observed in SSB, consistent with the spin singlet lifetime due to random nuclear spin fluctuations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773304]
Spin Bottleneck in Resonance Tunneling through In0.04Ga0.96As/GaAs Vertical Double Quantum Dots
(2011-01-01)
Huang, S. M.
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Tokura, Y.
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Akimoto, H.
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Kono, K.
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Lin, J. J.
We study the electron resonance tunneling through double quantum dots with different g factors. We found that the resonance tunneling current is suppressed even if one of the Zeeman sublevels is aligned. The level broadening effect partially releases the blockade. The current maximum peak appears when the interdot detune is half of Zeeman energy difference of two quantum dots.
Spin Bottleneck in Resonant Tunneling through Double Quantum Dots with Different Zeeman Splittings
(2010-04-02)
Huang, S. M.
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Tokura, Y.
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Akimoto, H.
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Kono, K.
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Lin, J. J.
We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels is aligned. This is because the other misaligned Zeeman sublevels limit the total current. A finite broadening of the misaligned sublevel partially relieves this bottleneck effect, and the maximum current is reached when interdot detuning is half the Zeeman energy difference.