Browsing by Author "Lin, Y. F."

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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.
Nanocontact resistance and structural disorder induced resistivity variation in metallic metal-oxide nanowires
(2009-11-11)
Lin, Y. F.
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Wu, Z. Y.
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Lin, K. C.
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Chen, C. C.
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Jian, W. B.
Several systems of metallic metal-oxide nanowires (NWs), including pure RuO(2) and as-implanted and annealed Ru(0.98)Cu(0.02)O(2) and Ru(0.93)Cu(0.07)O(2) NWs, have been employed in two-probe electrical characterizations by using a transmission electron microscope-scanning tunneling microscope technique with a gold tip. Thermal, mechanical, and electron beam exposing treatments are consecutively applied to reduce the electrical contact resistance, generated from the interface between the NW and the gold tip, so as to evaluate the intrinsic NW resistance. It is found that the residual contact resistance cannot be entirely removed. For each system of metallic metal-oxide NWs, several tens of NWs are applied to electrical characterizations and the total resistances unveil a linear dependence on the ratio of the length to the area of the NWs. As a result, the average resistivity and the contact resistance of the metallic metal-oxide NWs could be evaluated at room temperatures. The average resistivities of pure RuO(2) NWs agree well with the results obtained from standard two- and four-probe electrical-transport measurements. In addition, the as-implanted Cu-RuO(2) NWs reveal disordered crystalline structures in high-resolution TEM images and give higher resistivities in comparison with that of pure RuO(2) NWs. The residual contact resistances of all kinds of metallic metal-oxide NWs unveil, more surprisingly, an approximation value of several kilohms, even though the average resistivities of these NWs change by more than one order of magnitude. It is argued that the ductile gold tip makes one or more soft contacts on the stiff metal-oxide NWs with nanometer roughness and the nanocontacts on the NWs contribute to the electrical contact resistance.