ZnO nanocrystals synthesized by physical vapor deposition

Various types of zinc oxide (ZnO) nanocrystais were synthesized by physical vaporization of zinc powders without the presence of catalysts and a subsequent exposure to air at a high temperature. These crystals were found to be composed of ZnO nanowires, sheets, and tetrapods. They were observed to crystallize as wurtzite ZnO single crystals. The nanowires are about 120 nm in diameter on average and up to a few dozens of micrometers in length, making aspect ratios higher than 10. The growth direction of the nanowires was identified to be the [001] direction of wurtzite ZnO structure. It was found from microscopic analyses that these ZnO nanowires can be highly flexible. The values for the thickness of ZnO sheets are scattered, averaging 100 nm. The tetrapods may have a different number of projections radiating from one central node.