New Model for Reconstructed Si(111) 7 × 7 Surface Superlattices

Superlattices of disjoint bilayer atomic microdomains stabilized by epitaxial misfit strain energies are proposed to account for $n\times n$ ($n=5\mathrm{}$ at lower $T$, $n=7\mathrm{}$ at higher $T$) surface structures of both Si on Si(111) and Sn on Ge(111). The microdomain model accounts well for the relative stability of Si(111) 7×7 against hydrogenation and chlorination and is energetically more favorable than the original Lander model of 2×2 building blocks centered on point vacancies.