J. Libra

Au+ and Au3+ ions in CeO2 rf-sputtered thin films

The interaction of gold with CeO2 layers was investigated using photoelectron spectroscopy. 65 nm thick Au doped CeO2 layers were deposited by rf-magnetron sputtering on a Si(0 0 1) substrate by using a composite CeO2–Au target. The laboratory XPS and synchrotron radiation soft x-ray and hard x-ray photoemission spectra showed the formation of stoichiometric Ce4+ (CeO2) 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 Au0 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.

Interface termination and band alignment of epitaxially grown alumina films on Cu-Al alloy

Epitaxial ultrathin alumina films were grown on a Cu−9 at. % Al(111) substrate by selective oxidation of Al in the alloy in ultrahigh vacuum. The photoelectron spectra of Al 2p and valence band were measured in situ during oxidation. By analyzing multiple peaks of Al 2p, the interface atomic structure was discussed. The energy difference between the Fermi level of the substrate and the valence band maximum of alumina (band offset) was obtained. The relation between the interface atomic structure and the band offset was compared with the reported first-principles calculations. A novel method for controlling the band offset was proposed.

The growth of Au/Pd on alumina/Cu-Al system

We have studied thin layered Au/Pd/alumina/Cu-Al system by means of synchrotron radiation photoelectron spectroscopy (SRPES), X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). Ordered 0.8 nm thick alumina film was prepared by the controlled oxidation of the single-crystalline Cu-9at.%Al(111) support. The Pd and Au layers were prepared afterwards by a step-by-step deposition at room temperature. LEED measurement itself did not confirm epitaxial growth of the metal overlayers. They exhibited a pseudo layer-by-layer growth mode confirmed by work function measurements and the Monte Carlo simulation of the copper XPS peaks attenuation.