Uniform-height island growth of Pb on Si(111)-Pb(√3x√3) at low temperatures -: art. no. 155307

We have studied the growth of Pb on Si(111)-Pb(root 3x root3) at low temperatures, T<250K, and for coverages up to <theta>< 20 ML. The study is carried out with the complementary techniques of high-resolution low-energy electron diffraction and variable-temperature scanning tunneling microscopy. Uniform-height Pb islands, of flat tops and steep edges, are observed on this phase [similar to the uniform island growth observed on the Si(111)-(7x7)]. The origin of this unusual growth is quantum size effects (i.e., the dependence of the electron energy on the island thickness because of the quantization of the electron energy levels in the island). The preferred island height is five steps on the <root>3x root3 and seven steps on the (7x7) (for the same growth conditions T, theta) because of the different electronic structure at the two interfaces. Since different types of phases [i.e., (1 x 1), alpha-root 3x root3, which differ in the Ph stoichiometry] can form from the initial - root 3x root3 phase, with increasing coverage, the growth on these phases can be also used to study island-height selection. Laterally larger uniform-height islands are observed on the (1 x 1) at lower temperatures, T< 170 K; growth on the <alpha>-root 3x root3 at higher temperatures, T> 195 K, shows an open film with preference of the islands to grow to larger heights with uncovered regions of the alpha-root 3x root3 phase between the islands, even after deposition of 20 ML of Pb.