THE STRUCTURES AND CHEMICAL-STATES OF ULTRATHIN VANADIUM-OXIDES ON NI(110) SURFACE STUDIED BY LEED AND XPS

Ultrathin films of vanadium oxides (0.9-2.6 ML) grown on Ni(110) surfa ce have been studied using XPS and LEED. The 0.9 ML vanadium oxide pre pared by exposure of deposited vanadium atoms to 1 x 10(-5) Pa O-2 at 310 K acid then at 523 K, gives VO(111)-like oxide, as indicated by th e LEED pattern. The 1.7 ML oxide shows a VO(111)-(2 x 2) structure. Pr eparation of the oxide film at 623 K under 5 x 10(-4) Pa O-2 without a preoxidation at 310 K, leads to an LEED pattern with only streaks and to formation of approximate to 1.0 ML nickel oxide under the vanadium oxide. A single Ni 2P(3/2) peak of the nickel oxide shows a large che mical shift of approximate to 3.0 eV. The oxide film gives a streaky ( 1 x 6) pattern by heating at 773 K under 5 x 10(-4) Pa O-2 and a VO(11 1)-(2 x 2) pattern by heating at 673 K in vacuo. The reaction of the V O(111)-(2 x 2) surface with sodium atoms results in the formation of a n oxide containing Na+ and V5+ after heating at 473 K under 1 x 10(-5) Pa O-2. (C) 1997 Elsevier Science B.V.