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 (7×7) symmetry, the arsenic chemisorbed surface exhibits a (1×1) 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 0.2±0.1 AìŠ. © 1988 The American Physical Society.