Low energy ion scattering (LEIS) and Auger electron spectroscopy (AES) are applied to determine the surface composition of Pt25Ni75(100) and Pt25Ni75(110). After annealing at 970 K the topmost atomic layer of Pt25Ni75(100) is observed to be enriched in Pt to a value of 39 at %, whereas the first monolayer of Pt25Ni75(110) is found to consist nearly exclusively of Ni atoms. The second layer of the (110) surface shows strong Pt enrichment. The bombardement with low energy ions at room temperature induces the preferential sputtering of Ni atoms. The LEIS results indicate the superposition of the effects of preferential sputtering and segregation. The dependence of the surface composition on the annealing temperature is rather similar for both Pt25Ni75 crystals under investigation though the segregating component differs. Segregation is found to occur at rather low annealing temperatures, whereas high annealing temperatures are necessary to allow thermodynamic equilibration by bulk diffusion.
Corresponding author: W. Hofer (hofer).