Browsing by Author "Lu, Jia Grace"

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Electrical conduction mechanisms in natively doped ZnO nanowires (II)
(2010-04-09)
Tsai, Lin-Tzung
;
Chiu, Shao-Pin
;
Lu, Jia Grace
;
Lin, Juhn-Jong
;
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.
Quantum-interference transport through surface layers of indium-doped ZnO nanowires
(2013-06-21)
Chiu, Shao-Pin
;
Lu, Jia Grace
;
Lin, Juhn-Jong
;
電子物理學系
;
物理研究所
We have fabricated indium-doped ZnO (IZO) nanowires (NWs) and carried out four-probe electrical-transport measurements on two individual NWs with geometric diameters of approximate to 70 and approximate to 90 nm in a wide temperature T interval of 1-70 K. The NWs reveal overall charge conduction behavior characteristic of disordered metals. In addition to the T dependence of resistance R, we have measured the magnetoresistance (MR) in magnetic fields applied either perpendicular or parallel to the NW axis. Our R(T) and MR data in different T intervals are consistent with the theoretical predictions of the one- (1D), two- (2D) or three-dimensional (3D) weak-localization (WL) and the electron-electron interaction (EEI) effects. In particular, a few dimensionality crossovers in the two effects are observed. These crossover phenomena are consistent with the model of a 'core-shell-like structure' in individual IZO NWs, where an outer shell of thickness t (similar or equal to 15-17 nm) is responsible for the quantum-interference transport. In the WL effect, as the electron dephasing length L-phi gradually decreases with increasing T from the lowest measurement temperatures, a 1D-to-2D dimensionality crossover takes place around a characteristic temperature where L-phi approximately equals d, an effective NW diameter which is slightly smaller than the geometric diameter. As T further increases, a 2D-to-3D dimensionality crossover occurs around another characteristic temperature where L-phi approximately equals t (