Surface morphology of Pb overlayers grown on Si(100)-(2×1)

The behavior of Pb overlayers deposited on Si(100)-(2×{}1) at room temperature was investigated by scanning-tunneling microscopy and low-energy electron microscopy. Surface reconstructions of (2×{}2), c(4×{}8), (2×{}1), and c(4×{}4) were observed as Pb coverage increased from 0.5 to 1.5 monolayers. After the appearance of the c(4×{}4) phase, Pb islands with threefold-symmetric (111) orientation were observed on the twofold- or fourfold-symmetric Si(100) surface. The transformation of the island shape during growth can be broadly categorized as hexagonal{→}triangular{→}hexagonal. An internal structure of stepped-down depression was formed on all islands. As deposition continued, the depression was gradually filled by a step-flow growth mechanism. Our observations suggest that the initial growth of the islands is dominated by diffusion of Pb atoms on the substrate to the island edges; later, when the islands become sufficiently large, growth is determined mainly by atom diffusion on the Pb(111) islands.