Surfactant induced reversible changes of surface morphology

We have investigated the influence of a surfactant on the equilibrium surface morphology in the pseudomorphic regime of heteroepitaxial growth. At 700 ^∘{}C, 8 monolayers of Ge on Si(001) using Sb as surfactant form strained islands with a size of {~}300 {}, allowing partial elastic relaxation. The surface morphology depends strongly on the Sb coverage and changes from islands with [117] facets at high Sb coverage via round, flat cones with an inclination angle of 12^∘{} to islands rotated by 45^∘{} with [105] facets formed during growth at low Sb coverage. The equilibrium conditions are verified by the reversible transition from [117] facets to 12^∘{} cones initiated by a change of the surfactant coverage.