NiO-MgO and CoO-MgO Thin-Film Solid Oxide Solutions on a Mo(100) Support: Formation, Reduction, and Influence of the Support

We report on the formation, structure, composition, and reduction of NiO-MgO and CoO-MgO solid oxide solution thin films supported on a Mo(100) substrate. By use of a combination of grazing and normal emission X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory calculations we show that the Mo(100) support can exert a marked influence on the composition profile and reduction of the NiO-MgO solid oxide solution thin film. We find that the underlying Mo(100) support increases the stability of the Ni solute at the oxide film/Mo(100) interface relative to its stability in the MgO matrix. Further, we find that NiO is more easily reduced at the oxide film/Mo(100) interface than in the solid oxide solution film. These effects are the result of the large affinity of the Ni metal to the Mo support. XPS and STM measurements show a similar behavior for Mo(100)-supported CoO-MgO solid oxide solution thin films. The implications of these findings on the use of the...