Morphology and optical properties of ZnO nanostructures grown under zinc and oxygen-rich conditions

Zinc oxide nanostructures exhibit widely different morphologies and optical properties for different fabrication conditions. We investigated the influence of zinc and oxygen supply on the morphology and optical properties of zinc nanostructures. To minimize the number of parameters affecting the gas-phase supersaturation, vertical growth geometry with substrate placed at a fixed distance above the source was considered. Thus, source and substrate temperatures were kept the same (500 °C), while source-to-substrate distance, oxygen gas flow rate, and the amount of zinc source material were varied to change zinc and oxygen supply, and consequently change the gas-phase supersaturation and the properties of the obtained nanostructures. The morphology and optical properties of the nanostructures were studied using scanning electron microscopy and photoluminescence spectroscopy. Great variety of the morphologies was obtained, including ribbon/comb structures in spite of the low substrate temperature, and evolution of their morphology and optical properties as a function of oxygen-rich or zinc-rich growth conditions was discussed.