Scattered ion yields from bimetallic crystal surfaces

For a number of bimetallic single crystal surfaces and ordered epilayers we investigated scattered ion yields. He and Ne ions in the energy range of 1-4.5 keV were used to study the systems CuAu, PdRu, AuRu, NiAl and FeAl. Choosing appropriate scattering conditions the contributions from the topmost first and second atomic layers can be separated. Comparison of the measured ion yields for different elements or with numerical simulations that do not include neutralization effects provides the possibility to identify relative ion survival probabilities for scattering from different layers of these surfaces. The results show large differences for the various element and emphasize the importance of the chemical nature of first layer species for ion yields from second layer scattering. Au and Cu in the first layer cause a much higher neutralization rate than Al or Ru. Besides the relevance for neutralization processes these results are also important for quantitative analysis of alloy surface layers by low-energy ion scattering (LEIS).