AES Study of Room Temperature Oxygen Interaction with Near Noble Metal-Silicon Compounds Surface

We have carried out a comparative study of room temperature (RT) oxidation of near noble metal silicides similar in stoichiometry (M2Si) and electronic structure. Core-valence-valence (CVV) Auger line measurements on Ni2Si, Pd2Si and Pt2Si surfaces before and after exposure to 104 L of oxygen were performed. We compare the results with those for the oxidation of pure Si. In general oxygen interacts with Si atoms only. In Ni2Si, however, features ascribed to the onset of oxidation of Ni atoms appear in the Ni(MVV) line. In the Ni2Si and Pd2Si case, the Si reaction rate is increased with respect to that of pure Si, the strongest oxidation enhancement being obtained in Ni2Si. However, Si cannot be oxidized to SiO2 in these conditions; a SiOx (x < 2) phase is formed. The Pt2Si oxidation behaviour is close to that of pure Si. The different catalytic effect of Ni, Pd and Pt on Si oxidation has been discussed. We conclude that the main effect of metal is to by-pass the kinetic bottleneck of pure Si oxidation, i.e. the dissociation of the O2 molecule at the silicide/gas interface. The effect of different exposure procedures was also underlined.