Evolution of ZnO nanostructures on silicon substrate by vapor-solid mechanism: Structural and optical properties

ZnO nanostructures with different morphologies and sizes were synthesized on silicon substrate simply by the thermal evaporation of high-purity metallic zinc powder in the presence of oxygen without the use of any catalyst or additives. It was observed that the substrate temperature and the distance of the substrate from the source material play a critical role to determine the morphologies and sizes of the deposited structures. Scanning electron microscopic observations revealed that different types of nano- and microstructures, such as ZnO pyramid-shaped nanotowers, nanowires attached with the sheet-like structures, nanorods, microcages, and microtubes were obtained at different temperature zones with specific distances of the substrate from the source material. High-resolution transmission electron microscopy and x-ray diffraction studies confirm that the deposited products are single crystalline with wurtzite hexagonal structures. The room-temperature photoluminescence spectra of all the deposited structures displayed a strong near-band-edge emission with negligible green emission.