Structure and surface termination of ZnO films grown on (0001)- and (112¯0)-oriented Al2O3

We have studied the surface termination of ZnO(0001¯) films grown on Al2O3 substrates with high epitaxial quality. The structural properties of the ZnO films were investigated by X-ray scattering, revealing a predominant (0001¯)ZnO out-of-plane texture with the [112¯0]ZnO‖[0001]Al2O3 and [112¯0]ZnO‖[101¯0]Al2O3 azimuthal orientations for (112¯0)Al2O3 and(0001)Al2O3 substrates, respectively. The surface termination was determined by X-ray photoemission spectroscopy (XPS) via pyridine (C5H5N) adsorption at the ZnO surface. XPS data recorded at different temperatures after exposure to pyridine revealed that for both orientations of the Al2O3 substrates the deposited ZnO films were terminated by oxygen atoms, i.e. corresponding to a ZnO (0001¯) surface.