Oxidation of Ce on Si(111) studied by high-resolution photoelectron spectroscopy

The Si(111)–Ce (2×2) surface was studied by photoelectron spectroscopy during oxidation and annealing. Detailed analysis of the Si 2p core-level spectra and the Ce valence band levels shows that Ce is first oxidised and then promotes oxidation of Si at room temperature by improving the oxygen uptake of the surface. Initially, no oxidation of Si can be recorded, but at exposures of 3 L O2 or more, SiOx and higher silicon oxides are formed. After annealing to 750°C, a temperature that is generally used to oxidise Si, almost all O leaves the surface. At 1045°C, the Si 2p and the Ce valence band spectra of the sample show almost the same shape as for the original Si(111)–Ce 2×2 surface. This means that oxidation/reduction of the Si(111)–Ce 2×2 surface is reversible.