PREPARATION OF ULTRATHIN CHROMIUM-OXIDE FILMS ON CU(110) INVESTIGATEDBY XPS AND LEED

Ultra-thin chromium oxide films grown on Cu(110) have been investigate d 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 l ayer of the oxide shows a surface structure with hexagonal symmetry. T he major chromium component of the oxide was Cr2+ and the surface stru cture is ascribed to CrO(111)-like oxide. At the oxide coverage more t han 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 o f the chromium atoms to Cr3+. Th, surface oxide structure corresponds to the Cr2O3(111) surface. Both surface oxides are not stable to oxyge n exposure (similar to 1.3 x 10(-5) Pa) at above 473 K and a copper ox ide layer with Cu+ (one layer at maximum at 773 K) segregates to the t op of the chromium oxide as characterized by XPS and X-AES. Most of th e chromium atoms are reduced to Cr2+. The CrO(111)-like LEED pattern b ecome sharp. (C) 1998 Elsevier Science B.V. All rights reserved.