Morphological evolution of ZnO nanostructures: experimental and preliminary simulation studies

Abstract

ZnO nanostructures with various morphologies were prepared by thermal evaporation of Zn powders at 600 °C and atmospheric pressure without any catalysts. Field-emission scanning electron microscope images show various ZnO morphologies at both the downstream and upstream side of Zn sources. A continuous morphological transition from nails to needles was observed upstream. The morphologies downstream are nanopencils, and the tip of the pencils is smaller as the position approaches the Zn source. In general, the size upstream is larger than the one downstream. X-ray diffraction patterns indicate that all ZnO nanostructures grow preferentially along the [0001] direction. Room temperature photoluminescence spectra show that the intensity ratio of UV to green emission increases from the upstream products to the downstream products. The experimental results are elucidated through computational fluid dynamics simulation. Concentration fields of O₂ and Zn vapor show that the distributions of O₂ and Zn vapor are uneven upstream and uniform downstream.