After annealing at 970 K low energy ion scattering (LEIS) reveals the
topmost atomic layer of Pt25Ni75(100) to be
enriched in Pt to a value of 39 at%, whereas for
Pt25Ni75(110) the first monolayer is found to consist
nearly exclusively of Ni atoms and the second layer shows strong Pt
enrichment. LEIS measurements performed after ion bombardement at
room temperature indicate the superposition of the effects of
preferential sputtering of Ni atoms and segregation. Segregation is
found to start at rather low annealing temperatures, whereas high
annealing temperatures are necessary to allow thermodynamic
equilibration by bulk diffusion.
Most of the theoretical models fail to reproduce the orientation dependent change in the segregating component of the PtNi system. One of the few successful approaches is a thorough thermodynamic description which is used here to calculate the composition profile and to discuss the segregation behaviour. Good agreement between measurement and calculation is found.
Corresponding author: W. Hofer (hofer).