Results from low energy ion scattering spectroscopy of the surface composition of Pt10Ni90(110) are presented which - being performed at different scattering geometries - allow the derivation of the composition of the first and second layer. The PtNi system is an interesting example of an alternating segregation profile (reaching bulk concentration after a few layers) with an orientation-dependent change in the segregation component. Thus most theoretical descriptions fail. One of the very few successful models is a thorough thermodynamic description which will be used here in multilayer calculations. Good agreement between measurement and calculation is found, with strong Ni segregation in the topmost atomic layer and strong Pt enrichment in the second monolayer.
Corresponding author: W. Hofer (hofer).