MAM modelling of the segregation and ordering at the Pt Sn 111/ surface

The temperature dependent segregation and ordering phenomena at the Pt3Sn 111.surface are modelled by means of Monte Carlo simulations combined with the AMacroscopic AtomB Model MAM.. The results are compared with experimental data by Ceelen et al. wW.C.A.N. Ceelen, A.W. Denier van der Gon, M.A. Reijme, H.H. Brongersma, I. Spolveri, A. Atrei, U. Bardi, Surf. Sci. 406 1998.264x. It appears from the simulations that the experimentally observed 63=63.R308 structure at 700 K in the increasing temperature trajectory is a consequence of two factors: a preferential sputtering in the cleaning procedure and a limited atomic mobility, at lower temperatures restricted to the two outermost layers. It is thus induced by the sample preparation and hence merely an artefact rather than an intrinsic property. Only for temperatures between 1000 and 1200 K is full equilibrium between surface and bulk reached. The endothermic Sn segregation and corresponding 2=2.order at these temperatures are also evidenced in the MAM calculations that are in good agreement with the experimental data. q2000 Elsevier Science B.V. All rights reserved.