Browsing by Author "Kai, Ji-Jung"

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Contact to ZnO and intrinsic resistances of individual ZnO nanowires with a circular cross section
(2007-05-28)
Lin, Yen-Fu
;
Jian, Wen-Bin
;
Wang, C. P.
;
Suen, Yuen-Wuu
;
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.
Electron transport in high-resistance semiconductor nanowires through two-probe measurements
(2010)
Lin, Yen-Fu
;
Chen, Tzu-Han
;
Chang, Chia-Hung
;
Chang, Yu-Wei
;
Chiu, Yi-Cheng
Since the successful fabrication of semiconductor nanowires, various techniques have been developed to contact these nanowires and to probe their intrinsic electrical properties. Although many novel quasi one-dimensional materials such as Pb(1-x)Mn(x)Se nanoarrays were recently produced, their intrinsic electron transport properties have not been extensively studied so far. In this work, we demonstrate that an ordinary source-drain configuration of field-effect transistors or the two-probe measurement can be applied to the exploration of the intrinsic properties of nanowires. This two-probe measurement approach also works on highly resistive nanowires without an Ohmic contact issue. By using this method, electron transport behavior, resistivity, and carrier concentrations of ZnO, InP, GaP, and Pb(1-x)Mn(x)Se semiconductor nanowires have been investigated. Due to the tiny cross-section and few conducting channels, a nanomaterial usually reveals an ultra high resistance. This technique demonstrates a two-probe characterization of nanostructures, paving the simplest way toward electrical characterizations of all high-resistance nanomaterials such as deoxyribonucleic acid (DNA), molecules and organics.
Four-probe electrical-transport measurements on single indium tin oxide nanowires between 1.5 and 300 K
(2009-03-11)
Chiu, Shao-Pin
;
Chung, Hui-Fang
;
Lin, Yong-Han
;
Kai, Ji-Jung
;
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.
Growth of Cu nanobelt and Ag belt-like materials by surfactant-assisted galvanic reductions
(2007-05-08)
Huang, Ting-Kai
;
Cheng, Tzu-Hou
;
Yen, Ming-Yu
;
Hsiao, Wei-Han
;
Wang, Lung-Shen
We demonstrate the syntheses of single crystalline Cu nanobelt and Ag belt-like materials via CTAC-assisted (CTAC, cetyltrimethylammonium chloride) galvanic reductions. The single crystalline face-centered cubic phase Cu nanobelt was prepared by reacting CuCl2(aq) with Al(s) in an aqueous solution of CTAC and HNO3. The Cu nanobelt exhibited a high-quality ribbon-like nanostructure with a thickness less than 15 nm, a width of 30-150 nm, and a length up to 10 mu m. The belt-like Ag, with a thickness less than 10 nm, a width of 30-100 nm, a length up to 5 mu m, and a novel single crystalline 4H structure, was prepared by reacting AgNO3(aq) and Cu(s) in an aqueous solution of CTAC.
Growth of high-aspect-ratio gold nanowires on silicon by surfactant-assisted galvanic reductions
(2008-06-03)
Huang, Ting-Kai
;
Chen, Ying-Chieh
;
Ko, Hsin-Chun
;
Huang, Hsin-Wei
;
Wang, Chia-Hsin
A simple galvanic reduction for direct growth of An nanowires on silicon wafers is developed. The nanowires were prepared by reacting HAuCl4(aq) with Sn-(s) in the presence of CTAC((aq)) (cetyltrimethylammonium chloride) and NaNO3(aq), which were important to the product morphology development. The nanowire diameter was 50-100 nm, and the length was more than 20 mu m.
Growth of single-crystalline RuO2 nanowires with one- and two-nanocontact electrical characterizations
(2007-01-01)
Liu, Yee-Lang
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Wu, Zong-Yi
;
Lin, Kuei-Jiun
;
Huang, Jr-Jeng
;
Chen, Fu-Rong
Single-crystalline RuO2 nanowires were grown by using a thermal evaporation method. A control of the sizes (width and length) and the length-to-width ratio of the nanowires were achieved by tuning the growth time. A transmission electron microscope-scanning tunneling microscope technique invoking one-nanocontact electrical characterization was adopted to determine the room-temperature resistivity (similar to 100 mu Omega cm) of the nanowires. An e-beam lithography technique facilitating two-nanocontact measurements was performed to establish the metallic characteristic of individual nanowires. The authors found that a nanocontact may introduce high contact resistance, nonlinear current-voltage characteristics, and even semiconducting behavior in the temperature dependent resistance. (c) 2007 American Institute of Physics.
Size dependent magnetization and high-vacuum annealing enhanced ferromagnetism in Zn(1-x)Co(x)O nanowires
(2008-01-01)
Jian, Wen-Bin
;
Chen, I-Jan
;
Liao, Tai-Ching
;
Ou, Yi-Ching
;
Nien, Cheng-Hsun
Diameter controllable ZnO nanowires have been fabricated by thermal evaporation (vapor transport) with various sizes of gold nanoparticles as catalysts. Diluted magnetic semiconductor (DMS) Zn(1-x)Co(x)O nanowires were then made by high energy Co ion implantation. The as-implanted and the argon-annealed Zn(1-x)Co(x)O nanowires displayed weak ferromagnetism while the high-vacuum annealed nanowires exhibited strong ferromagnetic ordering at room temperature. Size dependent behavior has been observed in the magnetic field and temperature dependences of magnetization. The shrinkage of the nanowire diameter reduced the spontaneous magnetization as well as the hysteresis loops. Field cooled and zero-field cooled magnetization and coercivity measurements were performed between 2 and 300 K to study the evolution of magnetism from the weak to the strong ferromagnetic states. In particular, superparamagnetic features were observed and shown to be intrinsic characteristics of the DMS Zn(1-x)Co(x)O nanowires. The room-temperature spontaneous magnetization of individual Zn(1-x)Co(x)O nanowires was also established by using magnetic force microscope measurements.
Size effects on thermal treatments and room-temperature ferromagnetism in high-vacuum annealed ZnCoO nanowires
(2008-06-26)
Chen, I-Jan
;
Ou, Yi-Ching
;
Wu, Zhong-Yi
;
Chen, Fu-Rong
;
Kai, Ji-Jung
Zn0.92Co0.08O nanowires with two different average diameters, 19 and 38 nm, have been made by the vapor transport and Co ion implantation method. The as-implanted nanowires were thermally annealed through multiple steps in a high vacuum. The morphology and crystal structure of the nanowires were inspected by use of scanning and transmission electron microscopes. Electron microscopy analysis was used to ensure the absence of Co nanocrystals in the annealed nanowires. Measurements of temperature-dependent hysteresis were carried out to demonstrate a strong magnetic state in the high-vacuum annealed samples. The coercive field obeying a square-root temperature dependence and the room-temperature ferromagnetism have been discovered. Moreover, by comparison of magnetic properties between different-diameter nanowires, field-dependent magnetizations reveal considerably stronger ferromagnetism in the smaller diameter (19 nm) Zn0.92Co0.08O nanowires than that in the larger diameter (38 nm) nanowires. We argue that the generation of point defects by thermal annealing is the origin for the enhanced ferromagnetism in our high-vacuum annealed nanowires.
Valence state map of iron oxide thin film obtained from electron spectroscopy imaging series
(2007)
Chen, Ko-Feng
;
Lo, Shen-Chuan
;
Chang, Li
;
Egerton, Ray
;
Kai, Ji-Jung
This paper demonstrates the applicability of electron-spectroscopic imaging (ESI) for valence-state mapping of the iron oxide system. We have previously developed a set of signal-processing methods for an EST series, to allow mapping Of sp(2)/sp(3) ratio, dielectric function and energy bandgap. In this study, these methods are applied to generate a valence-state map of an iron oxide thin film (Fe/alpha-Fe2O3). Two problems, data undersampling and a convolution effect associated with extraction of the image-spectrum from the core loss image series, were overcome by using cubic-polynomial interpolation and maximum-entropy deconvolution. As a result, the reconstructed image-spectrum obtained from the EST series images has a quality as good as that of conventional electron energy-loss spectra. The L-3/L-2 ratio of the reconstructed EST spectrum is determined to be 3.30 +/- 0.30 and 5.0 +/- 0.30 for Fe and alpha-Fe2O3, respectively. Our L-3/L-2, ratio mapping shows an accurate correspondence across the Cu/Fe/alpha-Fe2O3 region. The effect of delocalization and chromatic aberration on the EST resolution is discussed and estimated to be about 2 nm for the case of L-3/L-2, ratio mapping. (c) 2006 Published by Elsevier Ltd.