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 12 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.

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