Browsing by Author "Lin, Juhn-Jong"

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1/f noise in micrometer-sized ultrathin indium tin oxide films
(2013-09-16)
Yeh, Sheng-Shiuan
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Hsu, Wei-Ming
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Lee, Jui-Kan
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Lee, Yao-Jen
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Lin, Juhn-Jong
We have measured the low-frequency noises of ultrathin indium tin oxide films to investigate the effect of post annealing on the noise level. The noises obtained obey an approximate 1/f law in the frequency range f approximate to 0.1-20 Hz. The microstructures and grain sizes of our films were altered by adjusting the annealing conditions. An enhancement of the noise level was observed for those samples comprising smaller grains, where numerous grain boundaries exist. This enhancement in the noise level is ascribed to atomic diffusion along grain boundaries or dynamics of two-level systems near the grain boundaries. (C) 2013 AIP Publishing LLC.
A critical path approach for elucidating the temperature dependence of granular hopping conduction
(2018-10-01)
Wu, Tsz Chun
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Lin, Juhn-Jong
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Sheng, Ping
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電子物理學系
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物理研究所
We revisit the classical problem of granular hopping conduction's sigma ae exp[-(T (o) /T)(1/2)] temperature dependence, where sigma denotes conductivity, T is temperature, and T (o) is a sample-dependent constant. By using the hopping conduction formulation in conjunction with the incorporation of the random potential that has been shown to exist in insulator-conductor composites, it is demonstrated that the widely observed temperature dependence of granular hopping conduction emerges very naturally through the immediate-neighbor critical-path argument. Here, immediate-neighbor pairs are defined to be those where a line connecting two grains does not cross or by-pass other grains, and the critical-path argument denotes the derivation of sample conductance based on the geometric percolation condition that is marked by the critical conduction path in a random granular composite. Simulations based on the exact electrical network evaluation of finite-sample conductance show that the configurationaveraged results agree well with those obtained using the immediate-neighbor critical-path method. Furthermore, the results obtained using both these methods show good agreement with experimental data on hopping conduction in a sputtered metal-insulator composite Ag (x) (SnO2)(1-x) , where x denotes the metal volume fraction. The present approach offers a relatively straightforward and simple explanation for the temperature behavior that has been widely observed over diverse material systems, but which has remained a puzzle in spite of the various efforts made to explain this phenomenon.
Activation Energy Distribution of Dynamical Structural Defects in RuO2 Films
(2018-09-05)
Yeh, Sheng-Shiuan
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Gao, Kuang Hong
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Wu, Tsung-Lin
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Su, Ta-Kang
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Lin, Juhn-Jong
Ruthenium dioxide (RuO2) is an important metal widely used in nanoelectronic devices. It plays indispensable roles in applications such as catalysts and supercapacitors. A good understanding of the origin of the flicker or 1/f noise in RuO2 will advance the design and efficiency of these applications. We demonstrate in a series of sputtered RuO2 polycrystalline films that the 1/f noise originates from fluctuating oxygen vacancies which act as dynamical structural defects, i.e., moving scattering centers. Reducing the number of oxygen vacancies by adjusting thermal annealing conditions significantly reduces the noise magnitude gamma, the Hooge parameter. We quantify the activation energy distribution function, g(E), and calculate the oxygen vacancy density, n(TLS), from the measured gamma value. We show that g(E) can be explicitly expressed in terms of gamma(T) and the electronic parameters of the metal, where T denotes temperature. The inferred n(TLS) value is in line with the oxygen content determined from the x-ray photoelectron spectroscopy studies.
Bistable transport properties of a quasi-one-dimensional Wigner solid on liquid helium under continuous driving
(2017-11-27)
Rees, David G.
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Yeh, Sheng-Shiuan
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Lee, Ban-Chen
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Kono, Kimitoshi
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Lin, Juhn-Jong
We investigate low-frequency fluctuations in the transport characteristics of a quasi-1D Wigner solid (WS) moving along a liquid helium substrate in response to a sinusoidal driving voltage. The fluctuations occur between distinct transport modes in which the decoupling of the WS from ripplonic polarons (or "dimple lattice," DL) formed on the helium surface does, or does not, occur during each ac cycle. We demonstrate that a Gaussian-like distribution in the decoupling threshold force gives rise to this bistability, as the low-frequency switching occurs when the probability of decoupling during each ac cycle is small but finite. We attribute the distribution in the decoupling threshold force to the range of structural configurations allowed for the quasi-1D electron lattice, which influences the strength of the WS-DL coupling. Hence, the switching rate between the ac transport modes is extremely sensitive to the microscopic properties of the electron solid.
Comment on 'Electron-phonon scattering in Sn-doped In(2)O(3) FET nanowires probed by temperature-dependent measurements'
(2009-11-18)
Lin, Juhn-Jong
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Wu, Chih-Yuan
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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 point out that the recently reported electrical quantities and transport behavior in a Sn-doped indium oxide FET nanowire (Berengue et al 2009 Nanotechnology 20 245706) should require serious reevaluation.
Comment on 'Electron-phonon scattering in Sn-doped In2O3 FET nanowires probed by temperature-dependent measurements'
(2009-11-18)
Lin, Juhn-Jong
;
Wu, Chih-Yuan
;
電子物理學系
;
物理研究所
;
Department of Electrophysics
We point out that the recently reported electrical quantities and transport behavior in a Sn-doped indium oxide FET nanowire (Berengue et al 2009 Nanotechnology 20 245706) should require serious reevaluation.
Conductivity and tunneling density of states in granular Cr films
(2010-08-12)
Sun, Yu-Chen
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Yeh, Sheng-Shiuan
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Lin, Juhn-Jong
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電子物理學系
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物理研究所
We have measured the tunneling differential conductances, G(V), of four Al/AlOx/Cr planar tunnel junctions as well as the conductivities, sigma(T), of the Cr electrodes at liquid-helium temperatures. The Cr electrodes were made to be granular with dimensionless intergrain tunneling conductance spanning from g similar or equal to 1 to g >> 1, and the dimensionality of the granular array d=3. For the samples with g >> 1, we found that the measured G(V) curves display large zero-bias singularities which obey a ln V law at low bias voltages (less than or similar to a few millielectron volt) while crossing over to a root V law at high bias voltages. Simultaneously, the conductivities of the Cr electrodes reveal ln T dependence below a characteristic temperature. These results are explained in terms of the recent theory of granular metals. In a sample with g similar or equal to 1, in addition to the conductivity dependence sigma proportional to ln T, we observed a universal scaling behavior of the normalized differential conductance [G(V, T) -G(0, T)]/root T with the combined parameter root e vertical bar V vertical bar/k(B)T in a wide temperature interval of 2.5-32 K. This result is not yet understood.
Contact to ZnO and intrinsic resistances of individual ZnO nanowires with a circular cross section
(2007-05-28)
Lin, Yen-Fu
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Jian, Wen-Bin
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Wang, C. P.
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Suen, Yuen-Wuu
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Wu, Zhong-Yi
Single crystalline ZnO nanowires (NWs) with a circular cross section and similar to 40 nm in diameter have been synthesized and utilized to fabricate two-contact ZnO NW devices. The electrical properties of the NW devices can be categorized into two classes according to the magnitude of their room-temperature resistances. I-V curves of low-resistance devices exhibit downward bending features and their temperature dependent resistances demonstrate thermal activation transport in the ZnO NWs. The high-resistance NW devices can be modeled as back-to-back Schottky contacts and the electron transport through the contacts reveals a variable-range-hopping mechanism. (C) 2007 American Institute of Physics.
Direct Observation of Electron Dephasing due to Inelastic Scattering from Defects in Weakly Disordered AuPd Wires
(2010-05-21)
Zhong, Yuan-Liang
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Sergeev, Andrei
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Chen, Chii-Dong
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Lin, Juhn-Jong
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電子物理學系
To identify and investigate the mechanisms of electron-phonon (e-ph) relaxation in weakly disordered metallic conductors, we measure the electron dephasing rate in a series of suspended and supported 15-nm thick AuPd wires. In a wide temperature range, from similar to 8 K to above 20 K, the e-ph interaction dominates in the dephasing processes. The corresponding relaxation rate reveals a quadratic temperature dependence, tau(-1)(e-ph) = A(ep)T(2), where A(ep) approximate to 5 x 10(9) K(-2) s(-1) is essentially the same for all samples studied. Our observations are shown to be in good agreement with the theory which predicts that, even in weakly disordered metallic structures at moderately low temperatures, the major mechanism of the e-ph relaxation is the electron scattering from vibrating defects and impurities.
Dynamical decoupling and recoupling of the Wigner solid to a liquid helium substrate
(2020-08-24)
Rees, David G.
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Yeh, Sheng-Shiuan
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Lee, Ban-Chen
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Schnyder, Simon K.
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Williams, Francis I. B.
We investigate the dynamical interaction between an electron crystal trapped above the surface of liquid helium and surface waves ('ripplons') excited by its motion. At rest, the electron system is 'dressed' by static ripplons to form 'ripplopolaron' states. As the electrons move, resonant ripplon scattering results in a growth of the ripplopolaron effective mass, on timescales comparable with the inverse of the ripplon frequency (similar to 100 ns). Under sufficient driving force, the electron system decouples from the surface waves and moves at high velocity, before decelerating sharply when the electron solid and surface excitations recouple to form a 'new' ripplopolaron system. The mass of the newly formed ripplopolarons is similar to that in the initial static case.
Effect of ion-milled barriers on electron transport in micrometer-sized tunnel junctions
(2014-03-12)
Lee, Yen-Chi
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Lin, Yong-Han
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Wu, Jong-Ching
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Lin, Juhn-Jong
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電子物理學系
We studied the electron transport properties of micrometre-sized all-Al tunnel junctions (TJs) between 2 and 300 K, in which the AlOx layer grown by O-2 plasma was moderately Ar-ion-milled prior to top electrode deposition. In contrast to the direct tunnelling in the TJs whose barriers are intact (not ion-milled), the zero-bias conductances and the current-voltage characteristics of the TJs as processed are found to be best described by the fluctuation-induced tunnelling conduction mechanism. This observation indicates the formation of nanoscopic incomplete pinholes in the AlOx layer, owing to large junction-barrier interfacial roughness introduced by the ion-milling process. Topographical features revealed by the cross-sectional transmission electron microscopy imaging of the TJ stack conform to this result. This study is of relevance to cases in which ion-milling techniques are applied in tailoring the TJ properties.
Effects of atomic scale imperfection at the interfaces of CoSi2 and Si (100) on Schottky barrier contacts
(2015-01-01)
Chiou, Chien-Jyun
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Chiu, Shao-Pin
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Lin, Juhn-Jong
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Chou, Yi-Chia
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電子物理學系
We report here the correlation of electrical properties on Schottky barrier contacts and atomic scale imperfections based on the degree of lattice distortion and moire fringes at the interfaces of CoSi2 and Si. The I-V measurements showed that the higher levels of perfection of the interfaces gave better Schottky barrier characteristics and we discuss the implications of the transport property at Schottky barrier contacts.
Electrical conduction mechanisms in natively doped ZnO nanowires (II)
(2010-04-09)
Tsai, Lin-Tzung
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Chiu, Shao-Pin
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Lu, Jia Grace
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Lin, Juhn-Jong
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電子物理學系
We have measured the intrinsic electrical resistivities, rho(T), of three individual single-crystalline ZnO nanowires (NWs) from 320 down to 1.3 K. The NWs were synthesized via carbon thermal chemical vapor deposition and the four-probe Pt contacting electrodes were made by the focused-ion-beam technique. Analysis of the overall temperature behavior of rho(T) confirms that the charge transport processes in natively doped ZnO NWs are due to a combination of the thermal activation conduction and the nearest-neighbor hopping conduction processes, as proposed and explained in a recent work (Chiu et al 2009 Nanotechnology 20 015203) where the ZnO NWs were grown by a different thermal evaporation method and the four-probe electrodes were made by the electron-beam lithography technique. Taken together, the observations of these two complementary studies firmly establish that the electrical conduction mechanisms in natively doped ZnO NWs are unique and now satisfactorily understood.
Electrical conduction processes in ZnO in a wide temperature range 20-500 K
(2011-09-15)
Lien, Chien-Chi
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Wu, Chih-Yuan
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Li, Zhi-Qing
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Lin, Juhn-Jong
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電子物理學系
We have investigated the electrical conduction processes in as-grown and thermally cycled ZnO single crystal as well as as-grown ZnO polycrystalline films over the wide temperature range 20-500 K. In the case of ZnO single crystal between 110 and 500 K, two types of thermal activation conduction processes are observed. This is explained in terms of the existence of both shallow donors and intermediately deep donors that are consecutively excited to the conduction band as the temperature increases. By measuring the resistivity rho(T) of a given single crystal after repeated thermal cycling in vacuum, we demonstrate that oxygen vacancies play an important role in governing the shallow donor concentrations but leave the activation energy (similar or equal to 27 +/- 2 meV) largely intact. In the case of polycrystalline films, two types of thermal activation conduction processes are also observed between similar to 150 and 500 K. Below similar to 150 K, we found an additional conductionprocess due to the nearest-neighbor-hopping conduction mechanism, which takes place in the shallow impurity band. As the temperature further decreases below similar to 80 K, a crossover to the Mott variable-range-hopping conduction process is observed. Taken together with our previous measurements on rho(T) of ZnO polycrystalline films in the temperature range 2-100 K [Y. L. Huang et al., J. Appl. Phys. 107, 063715 (2010)], this work establishes a quite complete picture of the overall electrical conduction mechanisms in the ZnO material from liquid-helium temperatures up to 500 K. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3638120]
Electron dephasing in homogeneous and inhomogeneous indium tin oxide thin films
(2012-03-05)
Wu, Chih-Yuan
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Lin, Bo-Tsung
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Zhang, Yu-Jie
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Li, Zhi-Qing
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Lin, Juhn-Jong
The electron dephasing processes in two-dimensional homogeneous and inhomogeneous indium tin oxide thin films have been investigated in a wide temperature range 0.3-90 K. We found that the small-energy-transfer electron-electron (e-e) scattering process dominated the dephasing from a few kelvins to several tens of kelvins. At higher temperatures, a crossover to the large-energy-transfer e-e scattering process was observed. Below about 1 to 2 K, the dephasing time tau(phi) revealed a very weak temperature dependence, which intriguingly scaled approximately with the inverse of the electron diffusion constant D, i.e., tau(phi)(T approximate to 0.3 K) proportional to 1/D. Theoretical implications of our results are discussed. The reason why the electron-phonon relaxation rate is negligibly weak in this low-carrier-concentration material is presented.
Electron-electron interaction effect on longitudinal and Hall transport in thin and thick Ag-x(SnO2)(1-x) granular metals
(2015-03-03)
Wu, Ya-Nan
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Wei, Yan-Fang
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Li, Zhi-Qing
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Lin, Juhn-Jong
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電子物理學系
We study the temperature behaviors of the Hall coefficient, R-H, and longitudinal conductivity, sigma, of two series of Ag-x(SnO2)(1-x) (x being the Ag volume fraction) granular films lying in the metallic regime. The first (second) series of films are similar to 500 (similar to 9) nm thick and constitute a three-(two-) dimensional granular array. In the high-x regime with g(T) >> g(T)(c) (g(T) being the dimensionless intergrain tunneling conductance, and g(T)(c) being the critical tunneling conductance at the percolation threshold), we observe a R-H alpha ln T law from similar to 6 to 300K. This ln T behavior is independent of array dimensionality. We also observe a sigma alpha ln T law in the temperature range similar to 20-100 K. Below similar to 10 K, the temperature behavior of sigma changes to a root T dependence in thick films, while it changes to a different ln T dependence in thin films. The overall R-H and sigma characteristics can be explained by the electron-electron interaction (EEI) effects in the presence of granularity. As x is reduced and approaches the percolation threshold, we found that the ln T dependences of R-H and sigma still hold for a wide temperature range. We propose an explanation for the long-standing puzzle of the sigma alpha ln T dependence, which has previously been frequently observed in composite systems near the quantum percolation threshold, as arising from the same EEI effect considered in the recent theory of granular metals.
Electronic conduction properties of indium tin oxide: single-particle and many-body transport
(2014-08-27)
Lin, Juhn-Jong
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Li, Zhi-Qing
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電子物理學系
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Department of Electrophysics
Indium tin oxide (Sn-doped In2O3-delta or ITO) is a very interesting and technologically important transparent conducting oxide. This class of material has been extensively investigated for decades, with research efforts mostly focusing on the application aspects. The fundamental issues of the electronic conduction properties of ITO from room temperature down to liquid-helium temperatures have rarely been addressed thus far. Studies of the electrical-transport properties over a wide range of temperature are essential to unravelling the underlying electronic dynamics and microscopic electronic parameters. In this topical review, we show that one can learn rich physics in ITO material, including the semi-classical Boltzmann transport, the quantum-interference electron transport, as well as the many-body Coulomb electron-electron interaction effects in the presence of disorder and inhomogeneity (granularity). To fully reveal the numerous avenues and unique opportunities that the ITO material has provided for fundamental condensed matter physics research, we demonstrate a variety of charge transport properties in different forms of ITO structures, including homogeneous polycrystalline thin and thick films, homogeneous single-crystalline nanowires and inhomogeneous ultrathin films. In this manner, we not only address new physics phenomena that can arise in ITO but also illustrate the versatility of the stable ITO material forms for potential technological applications. We emphasize that, microscopically, the novel and rich electronic conduction properties of ITO originate from the inherited robust free-electron-like energy bandstructure and low-carrier concentration (as compared with that in typical metals) characteristics of this class of material. Furthermore, a low carrier concentration leads to slow electron-phonon relaxation, which in turn causes the experimentally observed (i) a small residual resistance ratio, (ii) a linear electron diffusion thermoelectric power in a wide temperature range 1-300 K and (iii) a weak electron dephasing rate. We focus our discussion on the metallic-like ITO material.
Fluctuation-induced tunneling conduction through RuO(2) nanowire contacts
(2011-09-15)
Lin, Yong-Han
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Lin, Juhn-Jong
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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
A good understanding of the electronic conduction processes through nanocontacts is a crucial step for the implementation of functional nanoelectronic devices. We have studied the current-voltage (I-V) characteristics of nanocontacts between single metallic RuO(2) nanowires and contacting Au electrodes, which were pre-patterned by simple photolithography. Both the temperature behavior of contact resistance in the low-bias voltage ohmic regime and the I-V curves in the high-bias voltage non-ohmic regime have been investigated. We found that the electronic conduction processes in the wide temperature interval 1-300 K can be well described by the fluctuation-induced tunneling (FIT) conduction theory. Taken together with our previous work [Lin et al., Nanotechnology 19, 365201 (2008)], where the nanocontacts were fabricated by delicate electron-beam lithography, our study demonstrates the general validity of the FIT model in characterizing electronic nanocontacts. (C) 2011 American Institute of Physics. [doi:10.1063/1.3638707]
Fluctuation-induced tunneling conduction through RuO2 nanowire contacts
(2011-09-15)
Lin, Yong-Han
;
Lin, Juhn-Jong
;
電子物理學系
;
物理研究所
;
Department of Electrophysics
A good understanding of the electronic conduction processes through nanocontacts is a crucial step for the implementation of functional nanoelectronic devices. We have studied the current-voltage (I-V) characteristics of nanocontacts between single metallic RuO2 nanowires and contacting Au electrodes, which were pre-patterned by simple photolithography. Both the temperature behavior of contact resistance in the low-bias voltage ohmic regime and the I-V curves in the high-bias voltage non-ohmic regime have been investigated. We found that the electronic conduction processes in the wide temperature interval 1-300 K can be well described by the fluctuation-induced tunneling (FIT) conduction theory. Taken together with our previous work [Lin et al., Nanotechnology 19, 365201 (2008)], where the nanocontacts were fabricated by delicate electron-beam lithography, our study demonstrates the general validity of the FIT model in characterizing electronic nanocontacts. (C) 2011 American Institute of Physics. [doi:10.1063/1.3638707]
Four-probe electrical-transport measurements on single indium tin oxide nanowires between 1.5 and 300 K
(2009-03-11)
Chiu, Shao-Pin
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Chung, Hui-Fang
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Lin, Yong-Han
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Kai, Ji-Jung
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Chen, Fu-Rong
Single-crystalline indium tin oxide (ITO) nanowires (NWs) were grown by the standard thermal evaporation method. The as-grown NWs were typically 100-300 nm in diameter and a few mu m long. Four-probe submicron Ti/Au electrodes on individual NWs were fabricated by the electron-beam lithography technique. The resistivities of several single NWs have been measured from 300 down to 1.5 K. The results indicate that the as-grown ITO NWs are metallic, but disordered. The overall temperature behavior of resistivity can be described by the Bloch-Gruneisen law plus a low-temperature correction due to the scattering of electrons off dynamic point defects. This observation suggests the existence of numerous dynamic point defects in as-grown ITO NWs.