).
Low energy ion scattering spectroscopy results are presented which allow to derive the first and second layer's composition of the Pt10Ni90(110) single crystal. After annealing at 970 K the topmost layer is found to be nearly pure Ni, whereas the second layer shows a strong enrichment in Pt. After bombarding the surface with ions a similar depth profile is preserved with a slight Ni enrichment in the first monolayer. Thermal treatment of the sputtered surface induces at low temperatures site changes between first and second layer and at high temperatures equilibration between surface and bulk. Only very few theoretical models describe successfully the oscillating segregation profile and the orientation dependent segregating component of the PtNi system in the equilibrium state. A thorough thermodynamic description (previously applied in a monolayer approximation) will be used here in multilayer calculations to study the influence of the different effects on the composition profile. Pt and Ni differ negligibly in the surface free energies giving way to a competition between an ordering effect and a size effect. Good agreement between measurement and calculation is found.
Corresponding author: W. Hofer
(hofer).