Preparation of ultrathin nickel oxide on ordered vanadium oxide films grown on Cu(100) surface studied by LEED and XPS

Ordered ultrathin nickel oxide on vanadium oxide grown on a Cu(100) surface has been studied by XPS and LEED. One monolayer of vanadium oxide obtained by heating the vanadium atoms deposited on oxygen chemisorbed Cu(100) at 523 K under an O-2 atmosphere of 2 x 10(-5) Pa shows a chemical shift of the V 2p(2/3) peak which is smaller by 0.6 eV than that of bulk V2O3. A LEED measurement shows a pattern corresponding to two domains with a VO(111)-like surface structure rotating 30 degrees with respect to one another. At larger coverages an oxide of the VO(111)-(2x2) surface structure is formed upon healing at 573 K under the same oxygen atmosphere. Ultrathin, ordered nickel oxide films are prepared on the VO(111) and the VO(111)-(2 x 2) surfaces on Cu(100). On both vanadium oxides the similar to 0.8 to 2 ML nickel oxides take a NiO(lll)-like surface structure. The submonolayer nickel oxide gives a single Ni 2p(3/2) peak with a large chemical shift, such as 2.8 to 3.4 eV, being quite different in the binding energy and spectral features from the bulk NiO and 3-4 ML NiO on Ni single crystal surfaces. The electronic state of the nickel ions begins to change into the bulk-like state during the growth of the second layer.