Interaction of tungsten with CeO2(111) layers as a function of temperature: a photoelectron spectroscopy study

Abstract

The interaction of tungsten withCeO2(111) layers grown on Cu(111) was studied in the temperature range between 300 and 870 K byphotoelectron spectroscopy of the core levels and resonant valence band spectroscopy. Theinteraction was found to be very strong even at 300 K, leading to the formation of cerium tungstateCe6WO12 in which the metalatoms were in Ce3 + and W6 + chemical states. The growth was limited by the diffusion of W atomsinto the ceria layer, so subsequent tungsten deposition led to formationof W suboxides with consecutively lower chemical oxidation states, i.e. W4 + ,W2 + and metallicW0 with an almost negligiblecontribution of W5 + . Step-wise annealing of the layer showed that due to stimulated diffusion of tungsten into ceria at highertemperature, Ce6WO12 was formed more easily. Larger W overlayer thicknesses needed higher annealingtemperature to promote diffusion. The thickest sample studied, 1.4 nmW/CeO2, was transformed by annealing to 870 K to theCe6WO12/W system with a tungsten monoxide (WO) interface, whereas the rest of the tungsten was converted tothe W6 + oxidation state.