Formation of ZnO Nanosheets Grown by Catalyst-Assisted Pulsed Laser Deposition

We report on the growth of single-crystal ZnO nanosheets without stacking faults by Au-seeded pulsed laser deposition in a 0.5 mbar pure oxygen ambient, with their growth direction inclined to the ZnO[0001] crystalline axis. Changing the deposition ambient to 5% oxygen and 95% argon at the same total pressure led to formation of [0001]-oriented single-crystalline nanowires. We propose a formation mechanism for ZnO nanosheets based on superposition of catalyst-assisted growth beneath the Au droplet and asymmetric radial growth due to enhanced growth rates on exposed ZnO{0001} sidewall facets. The crystalline facets present at the Au-ZnO interface were found to be affected by the VI/II-ratio and seem to play an important role in determining the growth mode of the ZnO nanostructures. A possible mechanism for the formation of a rough Au-ZnO interface with facets different from those of ZnO (0001) is proposed, on the basis of convergence of the nucleation and step propagation rates at the growth front upon increasing the oxygen partial pressure.