Heteroepitaxial growth and surface electronic structures of ordered zinc oxide films on Mo(1Â 1Â 0) substrates

The preparation and surface electronic structures of ZnO thin films deposited on Mo(1 1 0) substrate by thermal evaporation under ultrahigh vacuum have been studied. Compared with insulating or semiconductive substrates, the metal substrate is of advantage to tune the surface electronic structures by electron spectroscopies owing to the elimination of surface charges. We found that 10−7 mbar or higher O2 pressure was necessary for the formation of stoichiometric ZnO films, and the corresponding epitaxial relationship was identified as ZnO(0 0 0 1)/Mo(1 1 0). Furthermore, the surface electronic states of ZnO films originating from interband transition, surface and bulk plasma were analyzed. We revealed that for the polar ZnO(0 0 0 1) surface, O-terminated ZnO monolayer with rock-salt structure at the topmost surface was thermodynamically stable, implying a transition from the wurtzite to the rock-salt structure at the surface.