Geometric structure of the Si(111): As-1 × 1 surface

Medium-energy ion scattering has been used to study the structure of the Si(111):As-1 ×{} 1 surface. The results are consistent with a surface model containing threefold-coordinated arsenic atoms in a substitutional first-layer site. A comparison of channeling and blocking data with Monte Carlo simulations shows an 0.24-{} expansion of the arsenic layer from unrelaxed bulk terminated silicon positions (30% of the bulk terminated first-to-second-layer spacing) and an arsenic one-dimensional vibration amplitude of 0.14 {}.