Preferential sputtering and segregation reversal: (100) and (110) surfaces of Pt₂₅Ni₇₅ single crystal alloys

P. Weigand, B. Jelinek, W. Hofer and P. Varga

Surf. Sci. 301 (1994) 306 - 312

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).