Reversible oxidation of WOx and MoOx nano phases

WOx and MoOx nano phases were prepared on TiO2(1 1 0) surfaces by a CVD procedure consisting of adsorption and decomposition of W(CO)6 or Mo(CO)6 precursors followed by annealing under UHV. Metal amount involved in each elaborated sample is in the fractional range from 0.1 to 0.35 equivalent monolayer (eqML) of W or Mo. Evolution of sample stoichiometry as a function of subsequent treatment is followed by valence band and core level photoemission as well as work function measurement. In each case, exposure of samples to molecular oxygen at room temperature induces an increase of sample work function in a range of several tenth of eV. Such a work function change is related to oxidation of sample involving both titanium and tungsten (or molybdenum) ions. Such an oxidation is reversible through an annealing under UHV at 470 K for molybdenum oxide and 670 K for tungsten oxide. Several cycles of exposure/annealing are possible without changes in work function or stoichiometry.