SURFACE CONCENTRATION MODIFICATION OF PTPD ALLOYS BY NOBLE-GAS ION SPUTTERING

The surface concentration of three PtxPd1-x alloys (x = 0.3, 0.5 and 0 .7) under ion bombardment was studied as a function of ion species and ion bombardment energy for the noble gas ions He, Ne, Ar and Xe in th e 0.5-1.25 keV energy range. The surface composition was measured by l ow-energy ion scattering spectroscopy (ISS) and Auger electron spectro scopy (AES). It was observed that Pd is preferentially sputtered from the surface of these alloys (as corroborated by previous studies). Thi s effect was found to be greatest for the lightest ion (He) and most p ronounced for the lowest energies used. Only a very weak dependence of the surface concentration on the energy of the heaviest ion (Xe) was detected. Comparing ISS and AES (true surface and near-surface informa tion respectively), it was also found that Pd is depleted in the near- surface region. The depletion is ascribed to radiation-enhanced diffus ion and segregation and it is shown how the overlaid contour mapping o f ISS and AES intensities, as a function of diffusion coefficient D an d segregation energy DELTAG, may be used to determine the radiation-in duced diffusion coefficient D as a function of ion species and ion ene rgy.