Lattice Gas Model Analysis of the (111) Surface Structures of Si, Ge and Related Systems

Abstract

The interrelation among the (2×8), (2×7) and (5×5) reconstruction states of the (111) surface of pure Ge, Si and related systems is discussed on the basis of the previously proposed lattice gas model. It is pointed out that the model corresponds to the two dimensional ANNNI model if interaction parameters stabilize these states as the ground state. It is shown that the (7×7) and (5×5) states correspond to networks of the walls separating the regions of different spin directions and the (2×8) one to a parallel configuration of the walls. It is conjectured on the basis of this correspondence that the floating phase discussed by Villain and Bak may exist in a temperature range inbetween the (2×8) phase and the disordered one in the case of Ge(111). Relevant experimental data are discussed.