ALUMINUM DEPOSITION ON NIO(100) - GROWTH, STRUCTURE AND COMPOSITION OF THE INTERFACE

Ultra-thin films were grown on stoichiometric NiO(100) single crystal surfaces by depositing aluminum at 250-degrees-C. The aluminum interacts very strongly with the NiO and an epitaxial Ni3Al(100) layer is formed at the interface. Reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) indicate that the film initially wets the NiO surface but quickly roughens with increasing film thickness. Photoemission (XPS and UPS) measurements show that the NiO substrate becomes Ni-deficient as the metallic Ni3Al phase grows by extracting Ni from the underlying NiO. Above an average film thickness of 10 monolayers, a polycrystalline aluminum layer forms on top of the Ni3Al phase when the Ni diffusion becomes rate limiting. Defects and non-stoichiometry on the NiO(100) surface intentionally created prior to growth affect the disorder and roughness of the growing film, but do not change the overall growth mechanism.