We will discuss two aspects of island or quantum dot formation on surfaces: the energetics of island formation in the Ge-Si system and the directed self assembly of islands on surfaces. We have determined the formation energies for Ge islands on Si {100} surfaces by combining continuum calculations of strain energy with first-principles-computed strain-dependent surface energies. The strain dependence of surface energy is critically impacted by the presence of strain-induced changes in the Ge {100} surface reconstruction. The appreciable strain dependencies of rebonded-step {105} and dimer-vacancy-line reconstructed {100} surface energies are estimated to give rise to a significant reduction in the surface contribution to island formation energies. We will also discuss methods to direct the self assembly dots on surfaces using strain patterning via embedded substrate inclusions, and morphologically patterned substrates. The three-dimensional calculations show that patterning in systems with nearly isotropic surface energy may result in ordered, self-organized quantum dot arrays. However, for systems with strong cubic surface energy anisotropy, the same patterning does not readily lead to an ordered array of pyramids.
Copyright. All Rights Reserved.