Si(111)-7 × 7 and Ge(111)-c(2 × 8) Surfaces

Abstract

In addition to the 2 × 1 reconstruction, which is observed after cleavage, silicon and germanium {111} surfaces possess 7 × 7 and c(2 × 8) reconstructions, respectively, after annealing treatments at elevated temperatures. The common feature of these large-unit-mesh reconstructions is the reduction of the number of dangling bonds per surface unit area by a factor of 2.6 and 2, respectively. The correlated lowering of the total energy is achieved by adatoms, each of which saturates three dangling bonds while it possesses one only. Such adatoms are naturally introducing surface strain. In c(2 × 8)-reconstructed Ge(111) surfaces, the related elastic energy is obviously overcompensated by the lowering of the band-structure energy due to the reduction of the density of dangling bonds. The 7 × 7 reconstruction, on the other hand, needs an additional decrease of the density of dangling bonds which is accomplished by the existence of surface dimers. Their formation needs the introduction of a stacking fault in half of the 7 × 7 unit mesh and the generation of a corner hole.