Large-scale synthesis and microstructure of SnO2 nanowires coated with quantum-sized ZnO nanocrystals on a mesh substrate.

Large-quantity single-crystal SnO(2) nanowires coated with quantum-sized ZnO nanocrystals (nc-ZnO/SnO(2) nanowires) were directly synthesized by thermal evaporation of SnO powder and a mixture of basic ZnCO(3) and graphite powders. A common stainless steel mesh was used to collect the products. The microstructure and possible growth mechanism of the nc-ZnO/SnO(2) nanowires were investigated. Results showed that tetragonal structured SnO(2) nanowires were obtained, whose surfaces were coated with single-layer ZnO nanocrystals with an average diameter of less than 5 nm. The nanowires had cross-rectangle section with width-to-thickness aspect ratio ranging from 2:1 to 5:1. The lengths of the nanowires were several tens of micrometers. ZnO nanocrystals were single crystalline wurtzite structures, which coated the whole nanowires and distributed uniformly. The possible growth mechanism of the composite nanowires may be enucleated that Zn atoms in the source vapor will replace the Sn atoms on the surface of the formed SnO(2) nanowires due to the higher reducibility of Zn than Sn. Two strong Raman scattering peaks at 626 and 656 cm(-1) appeared in the micro-Raman spectrum of nc-ZnO/SnO(2) nanowires. The origins of the peaks were discussed. Most importantly, the method can be extended to other composite oxide nanowires that are synthesized by oxidizing two kinds of metals, such as high reducibility elements Mg, Al, Zn, and Ti, and low reducibility elements In, Ge, Ga, etc.