Carbothermal Reduction Growth of ZnO Nanostructures on Sapphire

Zinc oxide (ZnO) nanostructures were grown by the vapour phase transport (VPT) method on a-plane sapphire substrates via carbothermal reduction of ZnO powders with various carbon powders. Specifically, graphite powder and activated charcoal powder (of larger total surface area but similar mesh size) were used. ZnO nanostructures can be grown at lower temperatures (∼800 °C) using activated charcoal than those required using graphite powder. Furthermore, the morphologies of ZnO nanostructures obtained using activated charcoal were different to those obtained using graphite. At higher temperatures (∼950 °C), where well-aligned nanorods were obtained using graphite powder, no nanostructures were found using activated charcoal. In contrast to previous results on Si substrates we find that the effects on ZnO nanostructure growth on a-sapphire cannot be explained solely in terms of increased Zn vapour pressure due to the enhancement of the carbothermal reduction reaction rate by the high surface area activated charcoal.

An effective approach is demonstrated for growing large-area, hexagonally patterned, aligned ZnO nanorods. The synthesis uses a catalyst template produced by a self-assembled monolayer of submicron spheres and guided vapor−liquid−solid (VLS) growth on a single crystal alumina substrate. The ZnO nanorods have uniform shape and length, align vertically on the substrate, and are distributed according to the pattern defined by the catalyst template. The nanorods grow along [0001] with side surfaces defined by {21̄1̄0}. This approach opens the possibility of creating patterned one-dimensional nanostructures for applications as sensor arrays, piezoelectric antenna arrays, optoelectronic devices, and interconnects.


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