Structure of Pt overlayers on ZnO(0001) and ZnO(000(1)over-bar) surfaces

The growth of Pt films on the Zn- and O-terminated polar surfaces of ZnO ha s been studied. Clean surfaces, prepared by sputtering and annealing, were dosed with Pt by vapor deposition. Properties of the film were examined by low-energy alkali ion scattering and low-energy electron diffraction. It is confirmed that, near room temperature, Pt grows on both surfaces as a sing le hexagonal layer which aligns with the substrate low index directions. Th e alignment is better for the Zn-terminated than for the O-terminated surfa ce. A Pt monolayer grows on the Zn-terminated surface until the ZnO surface is essentially covered with no evidence of a second Pt layer. Upon anneali ng above 675 K, Pt agglomerates into mostly bilayer islands, but maintains or improves its alignment with the substrate. Features associated with scat tering from bi- or multilayer Pt indicate that the Pt forms oriented (Ill)r afts. A coincidence LEED pattern indicates that the Pt lattice may be expan ded by 0.5% to form a 6:7 coincidence overlayer with the ZnO lattice.