Island-size distributions in submonolayer epitaxial growth: Influence of the mobility of small clusters

We examine the influence of dimer mobility on the size distribution of two-dimensional islands formed by irreversible nucleation and growth during deposition. We first characterize the transition in scaling of the mean island density with increasing dimer mobility, from the classic form described by Venables [Philos. Mag. 27, 697 (1973)] to the modified form for ''rapid'' mobility described by Villain et al. [J. Phys. (France) I 2, 2107 (1992)]. The corresponding transition in the asymptotic scaling function describing the shape of the island-size distribution is then also characterized. In addition, we contrast the mean-field form of the scaling function for rapid dimer mobility with that for zero mobility. Analysis of experimental data for Au/Au(100), Fe/Fe(100), Cu/Cu(100), and Pt/Pt(111) homoepitaxy reveals no clear evidence for a regime of modified island density scaling due to rapid dimer mobility. However, for Fe/Fe(100) below 400 K, we argue that mobility of small clusters significantly influences the shape of the island-size distribution, even before it affects the mean island density.