Interaction of oxygen with samarium on Al2O3 thin film grown on Ni3Al(111)

The interaction between oxygen and samarium (Sm) on the well-ordered thin Al2O3 film grown on Ni3Al(111) has been investigated by X-ray photoelectron spectroscopy and synchrotron radiation photoemission spectroscopy. At Sm coverage higher than one monolayer, exposure of oxygen to the Sm films at room temperature leads to the formation of both samarium peroxide (O22−) states and regular samarium oxide (O2−) states. By contrast, when exposing O2 to Sm film less than one monolayer on Al2O3, no O22− can be observed. Upon heating to higher temperatures, these metastable O22− states dissociate, supplying active O atoms which can diffuse through the Al2O3 thin film to further oxidize the underlying Ni3Al(111) substrate, leading to the significant increase of the Al2O3 thin film thickness. Therefore, it can be concluded that Sm, presumably in its peroxide form, acts as a catalyst for the further oxidation of the Ni3Al substrate by supplying the active oxygen species at elevated temperatures