SCALING OF ISLAND GROWTH IN PB OVERLAYERS ON CU(001)

The growth and ordering of a Pb layer deposited on Cu(001) at 150 K ha s been studied using atom beam scattering. At low coverage, ordered Pb islands with (sqaure-root 61 x square-root 61)R tan-1 (5/6) symmetry are formed. This is a high-order commensurate phase with 30 atoms in t he unit cell. From the measurement of the island diffraction peak prof iles we find a power law for the mean island size versus coverage with an exponent n = 0.54 +/- 0.03. A scaling behavior of growth is confir med and a simple model describing island growth is presented. Due to t he high degeneracy of the monolayer phase, different islands typically diffract incoherently. Therefore, when islands merge they still diffr act as separate islands and coalescence effects are thus suppressed. F rom the result for n we conclude that the island density is approximat ely a constant in the coverage range 0.1 < THETA < 0.5 where the order ed islands are observed [THETA is defined as the ratio between the num ber of Pb atoms and the number of Cu atoms in the underlying Cu(001) l ayer]. We thus conclude that most islands nucleate at THETA < 0.1 and then grow in an approximately self-similar fashion as THETA increases.