On the stability and structure of 5×5 and 7×7 reconstruction of the (111) surface of Si and Ge

Reconstructed surface structure of Si(111)-5×5-Ge and a 7×7 structure of the Ge(111) deposited on the Si(111) surface are confirmed to have atomic structures similar to a dimer adatom stacking-fault (DAS) structure of the Si(111)-7×7 surface. A structure model, dimer-chain model, which describes these DAS structures and a 2×8 structure having a similar atomic arrangement to DAS structure is presented. Stability of the dimer-chain structures with n×n (odd) and 2×m (even) periodicities is discussed using the Keating method. The result suggests structural change due to softening of the surface bonding.