STM study of Cu growth on the ZnO(1 0 1̄ 0) surface

The room temperature growth of Cu islands on the non-polar (1 0 1̄ 0) surface of zinc oxide was studied using scanning tunneling microscopy. Images of the clean (1 0 1̄ 0) surface prepared by sputtering and annealing at 550–700 °C exhibit flat terraces with a high density of steps, mostly running along [0 0 0 1] and [1 2̄ 1 0] directions. For Cu coverages of 0.025–1 ML deposited on flat, freshly annealed surfaces, preferential nucleation occurs at the step edges oriented perpendicular to the [1 2̄ 1 0] atomic row direction. Exclusively three-dimensional (3D) islands have been observed at all coverages. For comparison, the same Cu coverages were deposited onto the surface contaminated by adsorption from the residual gas in the ultrahigh vacuum chamber. Both 2D and 3D islands, randomly distributed across the terraces, were observed reproducibly on such slightly contaminated surfaces. The density of the islands, as well as their average diameter and height, increases with increasing Cu coverage for both surface preparations.