Sb-induced (1x1) reconstruction on Si(001)

We combine low-energy electron diffraction and reflectance anisotropy spectroscopy (RAS) with ab initio calculations of the geometry, band structure, and optical anisotropy to investigate the adsorption of Sb on vicinal Si(001) (1x2). We focus, in particular, on the controversy concerning the Si(001)-(1x1)-Sb surface. On the basis of total-energy and band-structure calculations, we find that the Sb-undimerised model is unstable and metallic, while experimentally the (1x1) Sb shows no evidence of a Fermi edge. In contrast, the dimerised (2x1)-Sb and c(2x2)-Sb reconstructions are found to be semiconducting with a minimal difference in total energy. Furthermore, the RAS spectra calculated for both dimerised reconstructions show strong similarities to one another, and agree well with the experimental RAS data for the Sb-induced (1x1)-Sb surface, with a dominant feature centered at 3.7 eV. We report that these findings are compatible with the (1x1)-Sb surface comprising a mixture of the Sb-dimer-terminated (2x1)-Sb and c(2x2)-Sb structures.