An AES (SAM), ESCA and ISS study of the oxidation of Pt 3 /Sn. 1: low pressure exposure to o 2

ESCA, ISS, AES and scanning Auger microscopy have been used to examine a sputter‐cleaned Pt 3 Sn alloy surface before and after exposure to oxygen at 10 −6 Torr. It is found that the amount of oxygen adsorbed on a sputtered surface is a strong function of sample temperature with a maximum at about 200°C. The clean surface consists of regions of varying Pt‐to‐Sn concentration ratios. Regions near grain boundaries are tin rich, and the tin concentration decreases in moving away from a grain boundary until a platinum‐rich region is reached. ESCA shows that an exposure to oxygen causes oxidation of the tin but no change in the Pt core‐level features. ISS shows that segregation of tin to the surface occurs and that the surface Pt concentration decreases due to coverage by the tin.