SODIUM ADSORPTION AND REACTION ON NIO(111)/NI(111)

Sodium adsorption and reaction on a NiO(111)/Ni(111) surface is studied via X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy (XAES). The observed work function decrease is similar to that for metals and semiconductors. However, the processes taking place on the oxide surface are more complex. At low and intermediate coverages Na becomes (partly) ionic and concomitantly reduces the Ni ions in the substrate near the surface to metallic Ni. This occurs at temperatures near 100 K. Eventually, Na2O is formed. At higher coverage the Na remains metallic. As the substrate is heated to T = 500 K, there are indications that a sodium nickelate is formed on the surface.