Formation of uniform nanoscale Si islands on a Si(111)-7 x 7 substrate

During epitaxial growth on a substrate with a stable surface structure, rearrangement from a superlattice to a normal 1x1 lattice is essential when the substrate is covered with a growing layer. Since rearrangement needs activation energy, lateral growth is prevented at the boundary of the structure unit. In the growth of Si on a stable 7x7 structure composed of a dimer-adatom-stacking- fault layer, lateral growth of islands is prevented at the dimer row. Such a restriction on the lateral growth leads to a discontinuous size distribution of islands, whose size depends on the size of the 7x7 structure unit. In the initial stage of nucleation and growth, we have observed many rounded Si islands with uniform diameters of 3.8 nm when the substrate temperature has been held at 380 degrees C for 10 min after deposition of Si. From the change in the island size distribution as a function of annealing time after the deposition, we conclude that the rounded island is constructed of atoms created by the dissociation of unstable small islands (< 40 atoms). (C) 1999 American Institute of Physics. [S0021-8979(99)06414-2].