Theory of the Sr-induced reconstruction of the Si (001) surface

By using first-principles calculations, we theoretically investigate the surface reconstruction caused by the adsorption of Sr on the Si (001) surface. For the Sr coverage below 1/ 2 monolayer (ML), the system behavior is dominated by the charge transfer between Sr and silicon that results in the "unbuckling" of Si dimers. At a higher coverage, the surface begins to "undimerize." At the 1 ML coverage, a geometric size constraint induces a series of reconstructions such as 3×, 5×, 7×, etc., characterized by 1×1 reconstructed patches separated by a dimer row. Calculations of the surface energy as function of coverage suggest that for 1 ML of Sr 3×, 5×, and 7× reconstructions of the surface are preferred under the Sr rich conditions, which is in good agreement with the experiment.