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Highly oriented copper nanowires were electrochemically synthesized in a porous alumina membrane template using a new type of weak-acid electrolyte. The Cu nanowires that were deposited have (110) preferred orientation, which is different from most electrochemically deposited Cu nanowires, and they can grow homogeneously. Transmission electron microscopy was used to investigate the room-temperature oxidation behavior, and it was observed that sample treatment methods greatly influence the oxidation rate of the wires. Cu nanowires with different diameters have different resistance to oxidation. The orientation relationship between oxide layer and small-diameter Cu nanowire was determined to be (001) Cu2O // (11¯1) Cu, (110) Cu2O // (110) Cu, and [1¯10] Cu2O // [1¯12] Cu. The possible oxidation process is also discussed. I. INTRODUCTION

Copper is a good conductor of heat and electricity (second only to silver in electrical conductivity), and it has long been used for interconnections in electronic circuits. It has been speculated that it may replace aluminum interconnections in integrated circuits. 1 Onedimensional (1D) nanostructures have received steadily growing interest as a result of their peculiar and fascinating properties, which are superior to their bulk counterparts.2–5 Different approaches have been successfully used to prepare Cu nanowires or nanorods, such as electrochemical deposition,6–10 reverse micelle methods,11–14 hydrothermal synthesis,15 electrical arc evaporation,16 solution-phase reaction,17,18 and DNA-templated construction.19 “Template synthesis,” coined by C.R. Martin, is a versatile chemical approach for the fabrication of nanostructures.20–22 Porous alumina membrane (PAM) is widely used as a template because it has highly regular pores that are almost perpendicular to the membrane surface; its porosity is also high. Electrochemical synthesis, which is widely used in electronic industry, is usually combined with PAM template to fabricate 1D nanostructures. Most importantly, PAM templates are easily integrated with silicon. There has been some research on fabricating alumina templates on silicon, and different metals have been electrodeposited in this templates.23,24

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Address all correspondence to this author. e-mail: [email protected] DOI:10.1557/JMR.2005.0288 J. Mater. Res., Vol. 20, No. 9, Sep 2005

http://journals.cambridge.org

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The thermal stability of 1D nanostructures is of critical importance for their implementation as building blocks in nanoscale electronic and photonic devices, and some research on thermal properties of 1D nanostructures has been carried out.25–30 For bulk Cu, it is well known that the compact Cu2O layer can dramatically reduce oxidation rates although it cannot completely prevent further oxidation. However, when the dimensionality is reduced to the nanometer scale, Cu is even more fragile to oxidation due to the high volume-to-surface area ratio. There is some research on room-temperature oxidation behavior of Cu nanowires. Bando et al.