A quasi 2-dimensional 4-state planar model was proposed for the study of (111)-NxN surface reconstructions, where N was equal to 5 or 7. Monte Carlo calculations showed that the model underwent a first-order phase transition that led to NxN structure formation at low temperatures. It also revealed the onset of stacking ordering at temperatures which were slightly higher than the critical point. By using the model, a natural candidate was identified for the substitution site of Ge atoms in the Ge/Si(111)-5x5 structure. That is, the substitution of Ge atoms in the structure appeared to take place at dimer sites, or at other sites which were directly related to their formation.

M.Itoh: Physical Review B, 1996, 54[8], 5873-80