SEGREGATION AT THE PT0.5NI0.5(111) SURFACE STUDIED BY MEDIUM-ENERGY ION-SCATTERING

Medium-energy ion scattering combined with shadowing and blocking is used to study the Pt-Ni alloy surface. By applying three scattering geometries in which different numbers of atomic layers are visible to the incoming ion beam, the compositions and relaxations of the first three layers of the crystal are accurately determined. An oscillating segregation profile is found in which (752)% Pt is present in the first layer, (273)% Pt in the second layer, and (535)% Pt in the third layer. The relaxations of the first and second interlayer distances amount to (-2.00.5)% and (-2.00.5)%. An enhancement of the thermal vibration amplitudes in the first three layers is found. The results support those obtained by other methods and agree with theoretical calculations. © 1990 The American Physical Society.