Promotion of the Si(100)-O2reaction by Sm

It is demonstrated that ultrathin and thin films of Sm on Si (100) strongly promote the oxidation of Si. Photoemission measurements of the Si 2p core electrons show binding-energy shifts characteristic of ${\mathrm{Si}}_2$ ${\mathrm{O}}_3$ and ${\mathrm{SiO}}_2$. The oxygen binding is conditioned by the presence of Sm, which is also oxidized. Reflection electron-energy-loss spectra and valence-band photoemission data indicate formation of an insulator with a valence-band maximum 4 eV below the Fermi level. The influences of samarium coverages, in the 1–20-monolayer regime, and of the temperature on the reaction are studied.