Au~+ and Au~(3+) ions in CeO_2 rf-sputtered thin films

摘要

The interaction of gold with CeO_2 layers was investigated using photoelectron spectroscopy. 65 nm thick Au doped CeO_2 layers were deposited by rf-magnetron sputtering on a Si(0 0 1) substrate by using a composite CeO_2_Au target. The laboratory XPS and synchrotron radiation soft x-ray and hard x-ray photoemission spectra showed the formation of stoichiometric Ce~(4+) (CeO_2) and the appearance of new Au~(+,3+) states with ionized Au species in excess of 50% of the total Au amount. Depth resolved measurements, by varying the emission angle or photon energy, indicated the formation of an Au~0 overlayer and deeper Au~(+,3+) species. The formation of Au~(+,3+) ions was found to be strongly dependent on the cerium oxide stoichiometry. The amount of ionized Au can be reversibly decreased and increased by surface reduction (removal of O by sputtering) and subsequent surface re-oxidation.