Stable structure of the Sb monolayer on a strained Ge(111) substrate

Using an ab initio total energy and force method, we have investigated the stability of different structures of Go(111):Sb(1 ML) as a function of the lateral lattice constant. We find that the (2x1)-reconstruction of Go(111);Sb, experimentally found to be stable at the equilibrium lattice constant of Ge, is also the stable structure for slightly dilated Go films (< 1%), while for larger dilatations the (1x1)-structure becomes stable. For compressed Ge films the (root3 x root3)T-4-structure (found experimentally on Si(111):Sb) becomes competitive and it is stable for the lattice constants compressed by more than 5%. Furthermore, we End that for each structure, the equilibrium lattice constant is different from the bulk Ge crystal. Our results are helpful for the understanding of surfactant mediated island growth on strained films.