SURFACE-STRUCTURE ANALYSIS OF SN ON NI(111) BY LOW-ENERGY ALKALI ION-SCATTERING

Low-energy Li+ ion scattering, LEED and AES were applied to analyze the surface structure of Sn on Ni(111). It was found that annealing Sn-covered surfaces with initial coverages from 1/3 to larger than 1 ML gave rise to a stable p(square-root 3 x square-root 3)R30-degrees LEED pattern with a coverage of 1/3 ML. Polar and azimuthal incidence angle dependences of Li+ ion scattering were measured for the clean and Sn-covered surfaces and were used to determine the surface geometry by analysis of shadowing and blocking features. The ion scattering data suggest that Sn incorporates into the first Ni layer but protruding 0.046 +/- 0.004 nm above the Ni plane for the p(square-root 3 x square-root 3)R30-degrees structure. The conclusion that Sn is incorporated was further confirmed by comparison with corresponding data obtained for p(2 x 2)-sulfur/Ni(111) known to form an overlayer structure and previous results for isostructural Sn/Pt(111).