The change of atomic structures and compositions of Pb,Sn/rSi 111/surfaces by thermal annealing

Changes of atomic structures and compositions of Pb,Sn.rSi 111.surfaces by isochronal annealing have been studied by means of low energy electron diffraction–Rutherford backscattering spectroscopy LEED–RBS.techniques. It is found that on isochronal annealing the Pb,Sn.rSi 111.surfaces show a new superstructure ofʹ7 =ʹ3 at Pb and Sn coverage of around 0.3 and 0.6 ML, respectively. Moreover, the Pb coverage on the Sn Si 111.ʹ7 =ʹ3 - Pb,Sn.surface decays at a temperature a little bit higher due to coexistence ofʹ7 =ʹ3 Pb atoms than that on the Si 111.ʹ3 =ʹ3 -Pb surface, while the Sn coverage shows a little decrease. These results suggest that the binary atoms of Pb and Sn form a 2-dimensional 2D. alloy on the Si 111.surface, in contrast to those of Ag and Cu which have a very similar bulk phase. q1998 Elsevier Science B.V. All rights reserved.