Ab initio study of the adsorption of In on the Si(0 0 1)-(2×2) surface

The adsorption of In on the Si(0 0 1)-(2×2) surface is studied, based upon ab initio pseudo-potential calculations. Of the two possible orientations for the In ad-dimers adsorption sites on this surface, viz. In ad-dimers parallel to the underlying Si dimer (model I) and In ad-dimers orthogonal to the underlying Si dimer (model II), we find model I to be energetically more favourable by 1 eV/ad-dimer. For model I, the Si–Si dimer becomes symmetric with an elongated bond length of 2.41 Å, and the In–In dimer is also essentially symmetric with a bond length of 2.74 Å. The Si–Si dimer bond length is somewhat bigger than the covalent diameter for Si while the In–In bond length is somewhat shorter than the atomic diameter for In. The calculated surface electronic structure and orbital bonding results support the available angle-resolved photoemission and scanning tunnelling spectroscopy measurements.