LEED structure determination of the Ni(111)(root 3 x root 3)R30 degrees-Sn surface

Quantitative low energy electron diffraction has been used to determine the structure of the Ni(1 1 1)(root3 x root3)R30degrees-Sn surface phase. The results confirm that the surface layer comprises a substitutional alloy of composition Ni2Sn as previously found by low energy ion scattering (LEIS), and also shows that there is no stacking fault at the substrate/ alloy interface as has been found in (root3 x root3)R30degrees-Sb surface alloys on Ag and Cu(1 1 1). The surface alloy layer is rumpled with the Sri atoms 0.45 +/- 0.03 Angstrom higher above the substrate than the surrounding Ni atoms. This rumpling amplitude is almost identical to that previously reported on the basis of the LEIS study. Comparison with similar results for Sn-induced surface alloy phases on Ni(1 0 0) and Ni(1 1 0) shows a clear trend to reduced rumpling with reduced surface atomic layer density, an effect which can be rationalised in terms of the different effects of valence electron charge smoothing at the surface. (C) 2003 Elsevier B.V. All rights reserved