Room temperature synthesis of ZnO nanoneedles by activated reactive evaporation

ZnO nanoneedles have been synthesized on glass substrates at room temperature by activated reactive evaporation. Neither a catalyst nor a template is employed in this synthesis. High-resolution transmission electron microscopy studies show that the ZnO nanoneedles are single crystalline in nature and that they grow along the [0 0 2] direction. We have investigated the effect of the surface roughness of the substrates on the morphology of the grown nanoneedles. This result suggests that the nanoneedles nucleate and grow in the gas phase rather than on the substrate by the vapour-solid mechanism. These gas phase grown nanoneedles are carried continuously by the flowing oxygen gas and are deposited as nanostructured films on the substrates kept at room temperature. Optical studies by Raman spectroscopy reveal that these nanoneedles are oxygen deficient in nature.