Photoemission study of Rh/CeO2/Cu(1 1 1) system-Oxidation state, stability and interaction with adsorbed gases

We have studied change of surface oxidation state of cerium oxide affected by Rh deposition, and interaction with gas molecules. Oriented films of CeO2(1 1 1)/Cu(1 1 1) were used as prepared (stoichiometric) as well as reduced by soft Ar+ sputtering. Rhodium was evaporated onto these, substrates. Prepared Rh/CeO2 samples were exposed to molecules CO and H2O. We have measured, core level, valence band and resonant photoemission spectra after every experimental step comparing, our results of the behaviour of both samples (stoichiometric and reduced before Rh deposition) with, regard to oxidation or reduction of the cerium oxide surface. We have demonstrated that resonant spectroscopy represents a good and sensitive tool to observe the, oxidation state of cerium providing tool for the interpretation of catalytic reaction.