The Investigation of Sm/Ni Model Catalysts : II. Adsorption of Oxygen and Properties of Oxidized Sm/Ni Films

The adsorption and reaction of oxygen on the Sm overlayer and Sm/Ni surface alloy have been investigated with AES and XPS. The sticking probability of oxygen on Sm/Ni surface alloys is significantly lower than that on the Sm overlayer. The strong interaction of adsorbed oxygen with Sm leads to segregation of Sm on the surface,which is confirmed by the depth profiling measurements. Annealing of the oxidized Sm/Ni surface alloys yields the agglomeration of Sm₂O₃ on the surface. XPS data release that the adsorption of oxygen gives rise to oxidation of the metallic Sm（III） to Sm⁺³ ion, while the oxygen apears as the O^-2ion in Sm₂O₃ phase and the chemisorbed O^- species on top of the oxide surface. Annealing the oxidized film induces removal of this chemisorbed oxygen into the bulk.