STRUCTURAL DETERMINATION OF A NIO(111) FILM ON NI(100) BY DYNAMICAL LOW-ENERGY ELECTRON-DIFFRACTION ANALYSIS

The geometric structure of a NiO(111) film on Ni(100) has been determi ned by dynamical low-energy electron-diffraction analysis. The oxide f ilm is sufficiently thick and uniform to carry out the analysis in the bulk crystal limit. Four orientational domains of NiO (111) are prese nt. We consider four possible terminations of the oxide film (oxygen o r nickel, fcc or hcp sites). Our results indicate that the oxide film terminates with a topmost layer of oxygen in fcc sites, and exhibits a 14.8% contraction in the first interlayer spacing relative to the ''b ulk'' interlayer spacing of the film. The ''bulk'' lattice parameters of the oxide film are found to be uniformly compressed by 2.6% relativ e to bulk NiO(111). Comparison with other work suggests that oxygen te rmination, a strong contraction in the first interlayer spacing, and r etention of cubic symmetry in deeper layers may be general characteris tics of unreconstructed rocksalt(111) surfaces of metal oxide films.