Tensor low energy electron diffraction and medium energy ion scattering determination of the Ni(110)c(2x2)-Sn surface structure

The Ni(110)c(2x2)-Sn surface phase has been investigated by the combination of quantitative low energy electron diffraction (LEED) with the aid of tensor LEED multiple scattering simulations, and medium energy ion scattering using 100 keV H+ incident ions. The structure is found to involve substitution of half of the outermost Ni atoms of the clean surface by Sn atoms, but the resulting single layer NiSn alloy is corrugated, with the Sn atoms being 0.40±0.03 A higher above the underlying Ni substrate than the outermost Ni atoms. The results are discussed in the context of previous structural studies of similar surface alloy phases; a weak trend for the amplitude of the corrugation in Ni/Sn surface alloys to become smaller as the surface layer packing density reduces may be consistent with previous ideas of the role of the depletion of valence electron density in the surface layer and the associated surface tensile stress. (author)