Structural perfection of the Si(111)-(1×1) As surface

We have used medium-energy ion scattering to determine the structure of the arsenic-saturated Si (111) surface. Unlike the clean surface, which is reconstructed with a (77) symmetry, the arsenic chemisorbed surface exhibits a (11) symmetry at near monolayer coverages. Ion-scattering yields show a decrease in the number of displaced silicon atoms due to a partial removal of the reconstruction accompanied by some disorder. The arsenic-silicon spacing is relaxed outwards from the bulk silicon interplanar spacing by 0. 20. 1 A.