The preparation of ultra-thin chromium–vanadium oxides on Cu(100) studied by XPS and LEED

Ultra-thin chromium and chromium–vanadium oxides have been grown on Cu(100) and characterized by XPS, X-AES and LEED. The chromium oxide was prepared by the oxidation of deposited chromium atoms on Cu(100) at 310 K, followed by annealing at 673 K in vacuum. At an oxide coverage of one layer, a weak LEED pattern ascribable to CrO(111) surface was observed. The chromium oxide containing Cr3+ was formed as well. At a coverage of more than two layers, a Cr2O3(111) surface was formed. When the Cu(100) substrate covered with the chromium oxide was heated in oxygen (∼1.3×10−5 Pa) at >473 K, a Cu+-oxide was formed on top of the chromium oxide. The ultra-thin chromium oxide was stabilized as a Cr2+-oxide between the copper substrate and the Cu+-oxide. The chromium–vanadium oxide assumed a surface structure like VO(111) at the total (chromium and vanadium) coverage of one layer and a surface like V3O4(111), similar to Fe3O4(111) structure at the larger coverage. The addition of the vanadium oxide to the chromium oxide increased the order of the surface structure of the oxide and prevented the copper substrate from the oxidation by the heating in oxygen (∼1.3×10−5 Pa) at 723 K.