Preferential sputtering and radiation enhanced segregation in palladium-platinum alloys

Abstract

Five palladium-platinum alloys of different compositions ranging from 10 to 90 at% Pd were sputtered with 1 keV Ar+ ions. The surface concentrations were then determined with Auger electron spectroscopy (AES) and low energy ion scattering spectroscopy (ISS). The observed concentrations differed largely from bulk values. This difference is explained in terms of the difference in sputtering yields for platinum and palladium and the radiation enhanced segregation of palladium. The surface was then mechanically cleaned in situ. The surface concentrations measured subsequently corresponded excellently with the bulk values confirming the calibration procedure for the calculation of the surface concentrations. A recently developed model for surface segregation was used to fit the experimental data. Values for the surface segregation energy ΔG and the radiation enhanced diffusion coefficient D were obtained in the range 2000–8000 Jmol and (1.2–8.0)×10−20m2s, respectively.