Modification of MoO3 surfaces by vapour-deposited cobalt atoms

The interaction of evaporated cobalt atoms with polycrystalline MoO3 surfac es was studied by means of X-ray photoelectron spectroscopy (XPS). In sever al steps cobalt was evaporated onto the clean MoO3 surface at 300 K, With i ncreasing cobalt layer thickness a shoulder in the Mo 3d spectra indicated the formation of Mo4+ and Mo5+ From the very beginning of the evaporation t he Co 2p spectra showed the appearance of Co2+ and at higher coverages that of Co-0. Subsequent stepwise annealing of the sample up to 800 K revealed that nearly the whole amount of Co-0 species is also oxidized and a non-sto ichiometric cobalt molybdate is formed. (C) 1999 Elsevier Science B.V. All rights reserved.