Preparation of ultrathin chromium oxide films on Cu(110) investigated by XPS and LEED

Ultra-thin chromium oxide films grown on Cu(110) have been investigated using XPS and LEED. The films are prepared by deposition of chromium atoms, exposure to oxygen and heating at 673 K in vacuum. The first layer of the oxide shows a surface structure with hexagonal symmetry. The major chromium component of the oxide was Cr2+ and the surface structure is ascribed to CrO(111)-like oxide. At the oxide coverage more than two layers, the LEED pattern transforms to a (root 3 x root 3)R30 degrees structure with respect to CrO(111) followed by the oxidation of the chromium atoms to Cr3+. Th, surface oxide structure corresponds to the Cr2O3(111) surface. Both surface oxides are not stable to oxygen exposure (similar to 1.3 x 10(-5) Pa) at above 473 K and a copper oxide layer with Cu+ (one layer at maximum at 773 K) segregates to the top of the chromium oxide as characterized by XPS and X-AES. Most of the chromium atoms are reduced to Cr2+. The CrO(111)-like LEED pattern become sharp. (C) 1998 Elsevier Science B.V. All rights reserved.