PARALLEL ADATOM CHAINS ON SI(111) - A CHEMISORPTION-INDUCED SURFACE RECONSTRUCTION

Using surface x-ray scattering, we have studied a (3 x 1) Si(111) reconstruction induced by chemisorption of CaF2. This reconstruction consists of a parallel array of zigzag Si adatom chains oriented along [110BAR]. The orbitals on the Si chain atoms rehybridize into p(x) and p(y) along the surface to form sigma bonds, and parallel sp(z) orbitals perpendicular to the surface to give additional pi bonding. This basic structure, with no dangling bonds at only 1/3 monolayer adsorbate coverage, may explain the occurrence of (3 x 1) reconstructions among a diverse range of Si-adsorbate systems.