SURFACE SEGREGATION OF PT10NI90(110) - EXPERIMENTAL AND THEORETICAL RESULTS

Results from low energy ion scattering spectroscopy of the surface com position of Pt10Ni90(110) are presented which - being performed at dif ferent scattering geometries - allow the derivation of the composition of the first and second layer. The PtNi system is an interesting exam ple of an alternating segregation profile (reaching bulk concentration after a few layers) with an orientation-dependent change in the segre gation component. Thus most theoretical descriptions fail. One of the very few successful models is a thorough thermodynamic description whi ch will be used here in multilayer calculations. Good agreement betwee n measurement and calculation is found, with strong Ni segregation in the topmost atomic layer and strong Pt enrichment in the second monola yer.