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

We have studied the growth of Pb on Si(111)-Pb(root 3x root3) at low temper atures, T<250K, and for coverages up to <theta>< 20 ML. The study is carrie d out with the complementary techniques of high-resolution low-energy elect ron diffraction and variable-temperature scanning tunneling microscopy. Uni form-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 depen dence of the electron energy on the island thickness because of the quantiz ation of the electron energy levels in the island). The preferred island he ight 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 st ructure 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 fro m the initial - root 3x root3 phase, with increasing coverage, the growth o n 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 tempera tures, 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 la rger heights with uncovered regions of the alpha-root 3x root3 phase betwee n the islands, even after deposition of 20 ML of Pb.