First principles calculations of the Sc adsorption on Si(001)-c(2 x 4)

We have investigated the energetics and the atomic structure of the adsorption of Sc on the Si(001)-c(2 x 4) surface using first principles total energy calculations, within the periodic density functional. The Sc adsorption has been studied at high symmetry sites considering different concentrations. We have first explored the one atom case and then increased the coverage up to a 0.25 of a monolayer of Sc. For the adsorption of one Sc atom we have obtained that the most stable configuration corresponds to the adsorption in the trench between two Si dimers, at the C1 (cave) site. The interaction of the adsorbed Sc with the Si dimers induces a decrease of the dimers buckling amplitude. On the other hand Si dimers without interaction with the adsorbate have buckling amplitudes similar to those of the clean Si surface. When the Sc coverage is increased to two Sc atoms, the most stable structure corresponds to the adsorption at two consecutive V (valley-bridge) sites along the trench between Si dimers, resulting in the weakening of some of the Si dimers bonds. This result indicates that the formation of one dimensional Sc chains on the silicon surface is energetically and kinetically favorable. (C) 2012 Elsevier B.V. All rights reserved.