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Crystalline CuO and Cu2O nanowires with an average diameter of about 10 nm and lengths of several tens of microns were successfully synthesized, depending on synthesis conditions, using precursor Cu(OH)2 nanowires as templates. The crystallinity, purity, morphology, and structural features of the as-prepared nanowires were characterized by powder x-ray diffraction, selected-area electron diffraction, and high-resolution transmission electron microscopy. The results showed that the precursor polycrystalline Cu(OH)2 nanowires served as both reactants for the growth of CuO and Cu2O nanowires, and as templates controlling the size and shape of the resulting nanowires.

One-dimensional (1D) nanoscale materials are currently of great interest due to their unique electronic, optical, and mechanical properties.1–7 Consequently, many 1D nanostructures such as carbon nanotubes,8–10 as well as inorganic nanowires/rods11–17 and nanotubes,18–21 have been synthesized through a variety of methods. Other recent efforts have focused on the synthesis of 1D nanoscale oxide architectures, see Ref. 22. Our interest lies in application of copper oxide nanostructures to achieve high-performance gas sensors; however, there are few published reports on routes for fabrication of 1D copper oxide nanostructures. In our previous work,23 we synthesized pure Cu2O nanowires using a wet chemical method in which the surfactant poly(ethylene glycol) (Mw 20 000) was used as a soft template. Recently it has been reported that a mixture of CuO and Cu2O nanowires, having a range of diameters from 30 nm to 100 nm, can be fabricated by heating a copper substrate in air.24 In this communication, we report on a novel fabrication route, which requires neither sophisticated techniques nor catalysts and surfactants, to selectively prepare two distinct wirelike copper oxides, either CuO or Cu2O depending on the synthesis conditions, with an average wire diameter of approximately 10 nm. The synthesis strategy for CuO and Cu2O nanowire fabrication starts with a sequence of reactions to first fabricate precursor Cu(OH)2 nanowires. The

precursor polycrystalline nanowires are used both as reactants for the growth of CuO and Cu2O nanowires and as templates controlling the size and shape of the resulting nanowires. CuO is a p-type semiconductor with a band gap of 1.2 eV commonly studied for its photoconductive properties.25,26 In particular, Cu2O and related materials are the subject of much current interest for use in highperformance batteries.27 Cu2O is a p-type semiconductor with a direct band gap of 2 eV, which makes it a promising material for the conversion of solar energy.28 Studies have shown that excitons can propagate coherently through Cu2O.29 For fabrication of the precursor Cu(OH)2 nanowires, the chemical reactions can be formulated as follows: 2Cu2+ + 2NH4共OH兲 → Cu2共OH兲22+ + 共NH4兲2+ ,

(1)

Cu2共OH兲22+ + 8NH3 → 2关Cu共NH3兲4兴2+ + 2OH− , 关Cu共NH3兲4兴2+ + 4 NH3

(2) (3)

,

Cu2+ + 2OH− → Cu共OH兲2

.

(4)

Using these prepared Cu(OH)2 nanowires as both reactants