Catalyst-free ZnO nanostructures were grown by pulsed-laser deposition on c-oriented sapphire. The nanostructure morphology can be controlled by introducing a nucleation layer. Depending on the doping concentration in the nucleation layer two distinct types of nanostructures are observed. On intrinsic nucleation layers nanowires form, while Al-doping results in a honeycomb network of nanoscale walls. From scanning-electron microscopy and X-ray photoelectron spectroscopy a correlation between nanostructure morphology and the polarity of the nucleation layers is derived.
ZnO nanostructures were grown by pulsed laser deposition on planar ZnO with different surface polarities. While for planar layers of pulsed laser deposited ZnO polarity control is feasible, the polarity relation of ZnO nanostructures to their substrate layers is not yet investigated. Depending on the polarity of the nucleation layer, two distinct morphologies were found, namely, nanorods on O-polar and nanowalls on Zn-polar ZnO. Convergent beam electron diffraction was performed to reveal the polarity of the ZnO nanostructures. The evolution of ZnO nanostructures is described in terms of a growth rate and a surface diffusion model.
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