PREFERENTIAL SPUTTERING AND SEGREGATION REVERSAL - (100) AND (110) SURFACES OF PT25NI75 SINGLE-CRYSTAL ALLOYS

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 P t25Ni75(100) is observed to be enriched in Pt to a value of 39 at%, wh ereas the first monolayer of Pt25Ni75(110) is found to consist nearly exclusively of Ni atoms. The second layer of the (110) surface shows s trong Pt enrichment. The bombardment with low energy ions at room temp erature induces the preferential sputtering of Ni atoms. The LEIS resu lts indicate the superposition of the effects of preferential sputteri ng and segregation. The dependence of the surface composition on the a nnealing temperature is rather similar for both Pt25Ni75 crystals unde r investigation though the segregating component differs. Segregation is found to occur at rather low annealing temperatures, whereas high a nnealing temperatures are necessary to allow thermodynamic equilibrati on by bulk diffusion.