Browsing by Author "Lin, JJ"

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A bi-level programming model for the land use - network design problem
(2003-03-01)
Lin, JJ
;
Feng, CM
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運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
A sketch map in urban planning roughly lays out a physical plan. However, the process of generating sketches has long been viewed as a "black box". The sketch layout model (SLM) was developed in 1999 to improve the efficiency and quality of layout tasks. This model is a nonlinear and multi-objective programming, for analyzing the integrated layouts of land uses, transport network and public facilities. Although the SLM had been developed for three phases and can be applied to real cases, the method still does not distinguish the types of roads in the transport network. This study develops the SLM-IV, a bi-level programming, by integrating the SLM-III and the combined trip distribution/assignment model, to generate a hierarchical network. This improved model can analyze travel demands, and then decide the link type of the network in SLM. A numerical example with relevant sensitivity analysis is presented to verify the operational feasibility and identify the model's characteristics.
A three-intensity technique for polarizer-sample-analyser photometric ellipsometry and polarimetry
(1998-08-21)
Chao, YF
;
Lee, WC
;
Hung, CS
;
Lin, JJ
;
交大名義發表
This work presents a novel three-intensity-measurement technique to determine the ellipsometric parameters psi and Delta in a polarizer-sample-analyser photometric ellipsometer. This technique can be employed to correct the azimuthal misalignment of the analyser with respect to the plane of incidence. By performing two sets of measurements with this technique with the polarizer's azimuth at +45 degrees and -45 degrees, respectively, we can simultaneously determine the azimuthal deviation of the polarizer and further improve the ellipsometric measurements. Applying this technique in the transmission mode allows us to obtain the phase retardation and the optical axis of a waveplate at the same time.
Anomalous temperature and disorder dependence of the electron-phonon scattering time in impure metals
(2003-05-01)
Lin, JJ
;
Zhong, YL
;
Kao, LY
;
Meikap, AK
;
物理研究所
We have measured the electron-phonon scattering time, tau(ep), in disordered metals at liquid-helium temperatures, using weak-localization method. The temperature and disorder dependence of tau(ep), is determined for AgPd and AuPd thick films, and V100-xAlx alloys. In all three cases, we find an anomalous temperature and disorder dependence of tau(ep)(-1) proportional to T(2)l where l is the electron elastic mean free path. This temperature and disorder behavior cannot be explained in terms of current theoretical concepts for the electron-phonon interaction in impure conductors. Current theory predicts a form of either tau(ep)(-1) proportional to T(4)l or tau(ep)(-1) proportional to T(2)l(-1) in the dirty limit, depending on the nature of the defects. (C) 2003 Elsevier Science B.V. All rights reserved.
Anomalous temperature and disorder dependences of electron-phonon scattering rate in impure V1-xAlx alloys
(2004-06-01)
Meikap, AK
;
Chen, YY
;
Lin, JJ
;
電子物理學系
;
物理研究所
Using weak-localization studies, we have measured the electron-phonon scattering time tau(ep) in a series of V1-xAlx alloys having the characteristic of ql<<1, where q is the wave number of the thermal phonons and l is the electron elastic mean free path. We find an anomalous electron-phonon scattering rate obeying a quadratic temperature dependence as well as a linear mean-free-path dependence, i.e., tau(ep)(-1)similar toT(2)l. This result cannot be explained in terms of existing theories for the electron-phonon interaction in impure conductors.
Comment on "Dephasing of conduction electrons due to zero-point fluctuation"
(2001-09-15)
Wu, GY
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Lin, JJ
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物理研究所
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Institute of Physics
It is recently proposed by Wang et al. [Phys, Rev. B 61 R5090 (2000)] that dephasing of conduction electrons due to zero-point fluctuation of electromagnetic field in a vacuum can well account for the measured saturation of electron dephasing time at T-->0 in various materials. We point out that this calculation is numerically incorrect. while we also provide arguments showing that zero-point fluctuation of electromagnetic field does not cause any dephasing within this theory of Wang et al.
Competition between the charge ordered and ferromagnetic states in (La,Nd)(0.75)Na0.25MnO3 manganites
(2004-05-24)
Li, ZQ
;
Zhang, XH
;
Yu, JS
;
Liu, XJ
;
Liu, XD
Structural, magnetic, and transport properties of (La1-xNdx)(0.75)Na0.25MnO3 (0 less than or equal to x less than or equal to 1) are studied. The system exhibits a rhombohedrally distorted perovskite structure for x less than or equal to 0.2 and it convert to an orthorhombic structure for x greater than or equal to 0.4. Re-entrant ferromagnetic type charge ordering transitions are observed in the narrow bandwidth samples (x greater than or equal to 0.6), while charge ordering transition is not observed for these samples with rhombohedral structure. Combining with the published results related to the charge ordering transition, we argue that the rhombohedral structure likely favor double exchange interaction and suppress charge ordering interaction. The compounds show metal to insulator transitions except Nd0.75Na0.25MnO3. The resistivity data above the metal to insulator transition temperature for the charge ordered sample are discussed in the frame work of variable-range hopping model. (C) 2004 Elsevier B.V. All rights reserved.
Direct observation of long-term durability of superconductivity in YBa2Cu3O7-Ag2O composites
(2003-10-01)
Lin, JJ
;
Lin, YH
;
Huang, SM
;
Lee, TC
;
Chen, TM
We report direct observation of long-term durability of superconductivity of several YBa2Cu3O7-Ag2O composites that were first prepared and studied almost fourteen years ago [J. J. Lin et al.: Jpn. J. Appl. Phys. 29 (1990) 497]. Remeasurements performed recently on both resistances and magnetizations indicate a sharp critical transition temperature at 91 K. We also find that such long-term environmental stability of high-temperature superconductivity can only be achieved in YBa2Cu3O7 with Ag2O addition, but not with pure Ag addition.
Direct observation of structure effect on ferromagnetism in Zn1-xCoxO nanowires
(2006-06-01)
Jian, WB
;
Wu, ZY
;
Huang, RT
;
Chen, FR
;
Kai, JJ
Diameter-controllable single-crystalline ZnO nanowires (NWs), with the [0001] growth direction in the plane, have been fabricated by using thermal evaporation method. The as-grown NWs with diameters of similar to 40 nm were implanted with various amounts of Co ions. These Zn1-xCoxO (x <= 0.11) NWs possessed a high density of bombardment-induced orientation variations and stacking faults, and exhibited paramagnetic behavior. After thermal annealing, the structural defects largely disappeared and noticeable hysteresis in the magnetization loops were observed, indicating the presence of apparent ferromagnetic ordering in the NWs. This result provides important insight into the role played by defects in relation to the occurrence of ferromagnetism in diluted magnetic semiconductor NWs.
Effect of annealing on electron dephasing in three-dimensional polycrystalline metals
(2002-03-01)
Lin, JJ
;
Zhong, YL
;
Li, TJ
;
電子物理學系
;
物理研究所
We have studied the effect of thermal annealing on electron dephasing times in three-dimensional polycrystalline metals. Measurements are performed on as-sputtered and annealed AuPd and Sb thick films, using the weak-localization method. In all samples, we find that possesses an extremely weak temperature dependence as T --> 0. Our results show that the effect of annealing is non-universal, and it depends strongly on the amount of disorder quenched in the microstructures during deposition. The observed saturation behavior of cannot be easily explained by magnetic scattering. We suggest that the issue of saturation can be better addressed in three-dimensional, rather than lower-dimensional, structures.
Effect of microstructure on the electron-phonon interaction in the disordered metals Pd60Ag40
(2002-10-01)
Zhong, YL
;
Lin, JJ
;
Kao, LY
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物理研究所
;
Institute of Physics
Using the weak-localization method, we have measured the electron-phonon scattering times tau(ep) in Pd60Ag40 thick films prepared by dc- and rf-sputtering deposition techniques. In both series of samples, we find an anomalous 1/tau(ep)proportional toT(2)l temperature and disorder dependence, where l is the electron elastic mean free path. This anomalous behavior cannot be explained in terms of the current concepts for the electron-phonon interaction in impure conductors. Our result also reveals that the strength of the electron-phonon coupling is much stronger in the dc- than rf-sputtered films, suggesting that the electron-phonon interaction is not only sensitive to the total level of disorder, but is also sensitive to the microscopic quality of the disorder.
Electrical resistivities and thermopowers of transparent Sn-doped indium oxide films
(2004-11-15)
Li, ZQ
;
Lin, JJ
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電子物理學系
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物理研究所
;
Department of Electrophysics
We have systematically measured the electrical resistivities and thermopowers of transparent tin-doped indium oxide films. We found that the resistivities obey the Bloch-Gruneisen law between 25 and 300 K, whereas below 25 K, the resistivities slightly increase logarithmically with the decreasing temperature due to the weak-localization and electron-electron interaction effects. The thermopowers are negative and decrease linearly with temperature from 300 K down to 1.8 K. Our results strongly indicate that the tin-doped indium oxide films behave as a good, free-electron-like conductor while being transparent. (C) 2004 American Institute of Physics.
Electron-electron interaction dominated quantum transport in thick CuGe films
(2000-07-01)
Hsu, SY
;
Shen, FJ
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Lin, JJ
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電子物理學系
;
物理研究所
We have successfully made a series of thick CuxGe100-x films spanning the weakly and strongly localized regimes. With decreasing mole concentration of Cu relative to Ge, the resistivity of film becomes bigger at a given temperature and demonstrates a stronger temperature dependence at low temperatures. When x is big, 46 less than or equal to x less than or equal to 56, resistivity increases with the square root of the decreasing temperature, implying a weak-disorder behavior. For x small, 14 less than or equal to x less than or equal to 2.0, resistivity increases exponentially with decreasing temperature, implying a strongly localized behavior. The results show that the low-temperature transport in these films is dominated by the disorder enhanced electron-electron interaction effects. (C) 2000 Elsevier Science B.V. All rights reserved.
Electron-electron scattering times in low-diffusivity thick RuO2 and IrO2 films
(1999-01-01)
Lin, JJ
;
Xu, W
;
Zhong, YL
;
Huang, JH
;
Huang, YS
We have systematically measured the electron dephasing scattering times from a three-dimensional weak-localization study of low-diffusivity thick RuO2 and IrO2 films. We find that the inelastic electron scattering rate 1/tau(in) varies essentially Linearly with the temperature and there is essentially no dependence of 1/tau(in) on the electron elastic mean free path. This observation is understood in terms of the current theoretical concept for electron-electron scattering in strongly disordered bulk conductors. [S0163-1829(99)02601-6].
Electron-phonon scattering times in crystalline disordered titanium alloys between 3 and 15 K
(1998-05-01)
Wu, CY
;
Jian, WB
;
Lin, JJ
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物理研究所
;
Institute of Physics
We have successfully fabricated bulk crystalline disordered titanium alloys (Ti1-xSnx, T1-xGex, and Ti0.97-xSn0.03Scx) with nominal concentration x of the order of a few at. %. The impurity atoms are gradually introduced into a titanium host to tune the degree of disorder, resulting in residual resistivities rho(0) varying from approximate to 40 to 160 mu Omega cm (corresponding to values of k(F)l approximate to 5-20, with k(F) being the Fermi wave number and l being the electron elastic mean free path). With this wide range of experimentally accessible rho(0), we are able to perform systematic studies of the disorder rho(0), or electron elastic mean free path l, behavior of the electron-phonon scattering time tau(ph). We have measured the magnetoresistivities of these alloys between 3 and 15 K, and compared our results with weak-localization theoretical predictions to extract tau(ph)(T,l) Unexpectedly, we obtain a rather diversified temperature dependence and disorder dependence of tau(ph) as follows. (a) In Ti1-xSnx alloys with rho(0) greater than or similar to 100 mu Omega cm we find 1/tau(ph)similar to T-2/l. (b) In Ti1-xSnx alloys with rho(0) less than or similar to 70 mu Omega cm we find 1/tau(ph)similar to T-3/l. (c) In Ti1-xGex alloys with 50 less than or similar to p(0) less than or similar to 130 mu Omega cm we find 1/tau(ph)similar to T-3 in some alloys and 1/tau(ph)similar to T-4 in others, while at a given temperature 1/tau(ph) is essentially independent of disorder. (d) In Ti0.97-xSn0.03Scx alloys with 55 less than or similar to rho(0) less than or similar to 75 mu Omega cm we obtain 1/tau(ph)similar to T-2. These experimental observations altogether imply that electron-phonon interactions in the presence of strong impurity scattering are very sensitive to the local material environment (the microscopic quality) of a particular sample system, which might be variously modulated with the doping of different kinds of impurity atoms. Our results are compared with existing theoretical predictions for electron-phonon scattering in disordered conductors.
Electron-phonon scattering times in three-dimensional disordered Sb films
(2000-02-01)
Lin, JJ
;
Li, TJ
;
Wu, TM
;
電子物理學系
;
物理研究所
We have measured the electron-phonon scattering times t(ep) in a series of three-dimensional Sb films having the characteristic of ql similar to 1, where q is the wave number of the thermal phonons, and I is the electron elastic mean free path. We observe that 1/t(ep) similar to T-p, With P approximate to 2.4, in the temperature range 1-14 K. In addition, we find a very weak dependence of 1/t(ep) on l. Our observations are compared with theoretical predictions for electronphonon interactions in the presence of disorder and with previous experimental results in thin Sb films.
Electron-phonon-impurity interference effect in disordered Au56Pd44 and IrO2 thick films
(2005-07-01)
Yeh, SS
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Lin, JJ
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Jing, XN
;
Zhang, DL
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電子物理學系
We have fabricated a series of Au56Pd44 thick films with a wide range of residual resistivity rho(0) varying from 40 to 280 mu Omega cm. The resistivities of these films were measured between 15 and 300 K. We found that at temperatures below about 0.1 theta(D) (theta(D) is the Debye temperature), the interference mechanism between the elastic electron scattering and electron-phonon scattering (the electron-phonon-impurity interference effect) contributes significantly to the measured resistivities. Our results support the current theoretical idea that this interference-mechanism-induced resistivity varies with rho(0)T(2), where T is the temperature. Similar observation has also been made in disordered, conducting transition-metal oxide IrO2 thick films.
Electronic transport in insulating AlPdRe quasicrystals
(2004-02-18)
Rosenbaum, R
;
Murphy, T
;
Brandt, B
;
Wang, CR
;
Zhong, YL
Resistivity and magnetoresistance measurements have been performed on insulating icosahedral AlPdRe quasicrystal (QC) bar samples. At temperatures in the range 300 K greater than or equal to T greater than or equal to 50 K, the resistivities follow a simple inverse temperature law: rho(T) rho(0)/T(1.0+/-0.1). Below 1 K, the resistivity of a weakly insulating sample exhibited a simple inverse temperature law where rho(T) = rho0/T-0.33 and not an activated variable-range hopping (VRH) law. Strongly insulating samples exhibit saturation of their resistivities to finite values as T --> 0 K. These saturation resistivity values are believed to arise from the presence of a second metallic phase located within the quasicrystal's structure. By extrapolating the measured resistivities at 22 mK to absolute zero, the saturation conductivity values were estimated at T = 0 K and subtracted from the conductivity data points. These 'corrected' data, corresponding only to the QC phase, were found to follow activated VRH laws, having hopping exponents y that vary in the range 0.18 less than or equal to y less than or equal to 0.43. The activated VRH behaviours are observed only below 1 K. The magnetoresistances (MRs) of these samples are also anomalous. The MRs can be explained by including contributions from both the saturation conductivity values and from the QC MR ratios, estimated using the wavefunction shrinkage model.
Electronic transport properties of alpha-TiAl alloys
(2005-10-10)
Zhang, DL
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Liu, SM
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Jing, XN
;
Luo, JL
;
Zhang, XG
The electrical resistivity, thermal conductivity, and thermopower of alpha-TiAl alloy samples with A1 content from 0 at.% to 10 at.% are measured from room temperature down to liquid helium temperature. It is found that with the increase in A1 content the single phonon scattering contribution to the resistivity remains nearly constant, but the multiphonon scattering contribution monotonously increases. This provides an alternative explanation of resistivity saturation to the shunt-resistor model. The Wiedemann-Ranz law holds for the whole temperature range, allowing the separation of the electron and phonon contributions to the thermal conductivity. The data from samples with different doping levels enable us to separate the band and the scattering terms in the thermopower.
Electronic transport studies on Sb1-x(SiO2)(x) films
(2005-05-04)
Du, J
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Li, ZQ
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Lin, JJ
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Liu, H
;
Zheng, RK
Sb1-x(SiO2)(x) granular films were prepared by the co-sputtering method with the volume fraction of SiO2, x, ranging from 0 (i.e. pure Sb) to about 30 %. Systematic electronic transport studies, including resistivity, magnetoresistance, Hall effect and Seebeck effect, were carried out against the temperature, magnetic field and volume fraction x of SiO2. With the gradual increase of the SiO2 content, the mean grain size of the Sb decreases, and eventually the film becomes amorphous, as illustrated by the changes of the x-ray diffraction patterns. The temperature coefficient of resistivity also changes its sign from positive to negative, indicating a semimetal-semiconductor or insulator transition. Magnetoresistance studies using the weak localization theory revealed that the electron dephasing time follows approximately a T-2 law. This behaviour indicates that the electron-phonon (e-ph) scattering still dominates the electron dephasing processes in these granular systems with a fair number of SiO2 inclusions. The Hall coefficient decreases monotonically with temperature and with the volume fraction of SiO2. The giant Hall effect is absent in these granular films. Finally, an interesting but rather complicated behaviour of the Seebeck coefficient versus temperature was observed when the volume content of the SiO2 exceeded 18 %.
Electrostatic dissipation and flexibility of poly(oxyalkylene)amine segmented epoxy derivatives
(2000-04-01)
Lin, JJ
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Tseng, FP
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Chang, FC
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應用化學系
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Department of Applied Chemistry
A family of hydrophilic and flexible epoxy polymers was prepared from the reaction of poly(oxyalkylene)amines and diglycidyl ether of bisphenol-A (DGEBA) at 1:1 molar ratio of N-H to epoxide. The use of a high molecular weight (M-W = 1000-6000) poly(oxyethylene-oxypropylene)amine and a low M-W amine as curing agents provided epoxy materials with good properties in toughness and hydrophilicity. The hydrophilicity, probed by surface resistivity of these cured materials, was found to be affected by the nature and weight content of poly(oxyethylene) segment in the polymer backbone, and also by the degree of crystallinity. Specifically, in the presence of a water-soluble poly(oxyethylene-oxypropylene)diamine of M-W 2000 the cured epoxies can reach surface resistivity as low as 10(8.6-9.6) Omega/square. In comparison, the water-insoluble poly(oxypropylene) diamine of M-W 2000 afforded a higher surface resistivity of 10(10.5) Omega/square because of the difference in hydrophilicity between oxyethylene and oxypropylene functionalities. Poly(oxypropylene)diamine of M-W 230 as the sole curing agent generated an epoxy with even higher surface resistivity of 10(13) Omega/square due to a highly crosslinking structure. With proper selection of mixed poly(oxyethylene-oxypropylene)diamine (25 wt%) and 2-aminoethanol (9 wt%), the DGEBA cured polymer had an appropriate surface resistivity of 10(9.8) Omega/square for antistatics. Moreover, this material was extremely ductile in appearance and showed over 500% elongation at break during mechanical tests. The high flexibility is rationalized by the balanced chemical structure of poly(oxyalkylene) segments and bisphenol-A distributed in a slightly crosslinked system. (C) 2000 Society of Chemical Industry.