SURFACE STRESSES IN ATOMIC RECONSTRUCTIONS OF LEAD ON SILICON (111)

We have measured the intrinsic surface stresses associated with reconstructions of Pb adsorbed on Si(111). By measuring the stress in two different cube-root x cube-root 3 reconstructions having 1/3 and 1/6 ML Pb coverage, we find that both Pb and Si adatoms contribute identical surface stresses of 1.75 +/- 0.20 eV/1 x 1 cell. This value is in excellent agreement with theoretical calculations for Si adatoms in the cube-root x cube-root reconstruction. A comparison with calculations for Ga cube-root x cube-root adatoms shows that the electronic hybridization of the adsorbate atoms is more important than the adatom size in determining the surface stress. We also determine that the rotated incommensurate phase having approximately 1 ML of Pb on Si(111) has a surface stress of 1.24 +/- 0.10 eV/1 x 1 cell, which is comparable to that of an incommensurate reconstruction of Ga on Si(111). The similarities in these stresses, despite differences in the two incommensurate structures, indicate that the overlayer is effectively decoupled from the substrate in both incommensurate reconstructions.