Optimized structures and electronic properties of alkali-metal (Na, K) -adsorbed Si(001) surfaces

Structural determination of the low-coverage phase of Al on Si(001) surface

The atomic structure of Al layer on Si(001)-(2 x 1) surface has been studied by coaxial impact collision ion scattering spectroscopy. When 0.5 monolayer (ML) of Al atoms are adsorbed on Si(001) at room temperature, it is found that Al adatoms are dimerized and Al ad-dimers are oriented parallel to the underlying Si dimers at the position of centering T3 site with a height of 1.02 Angstroms from the first layer of Si(001). The bond length of the Al dimer is 2.67 Angstroms. With increasing Al coverage up to one ML, Al ad-dimers still occupied near T3 site and the next favorable site is near HH site.

First-principles study of the adsorption of cesium on Si(001)(2×1) surface

First-principles calculations based on density functional theory-generalized gradient approximation method have been performed on cesium adsorption on Si(001)(2 x 1) surface. The optimized geometries and adsorption energies have been obtained and the preferred binding sites have been determined for the coverage (Theta) of one monolayer and half a monolayer. At Theta = 0.5 ML the most stable adsorption site is shown to be T3 site. At Theta = 1 ML two Cs atoms are adsorbed at HH and T3 sites, respectively. It was found that the saturation coverage of Cs for the Si(001)(2 x 1)-Cs surface is one monolayer instead of half a monolayer. This finding supports the majority of experimental observations but does not support recent coaxial impact collision ion scattering spectroscopy investigations [Surf. Sci. 531, L340 (2003)] and He(+) Rutherford backscattering spectroscopy studies [Phys. Rev. B 62, 4545 (2000)]. Mulliken charge and overlap population analysis showed that the Cs-Si bond is indeed ionic rather than polarized covalent as generally assumed for alkali metal (AM) on Si(001)(2 x 1) surface. Geometrical structure analysis seems to have limitations in determining the nature of AM-substrate bond. We also found that the silicon surface is metallic and semiconducting for the coverages of 0.5 and 1 ML, respectively.