Kinetics of two-dimensional island nucleation on reconstructed surfaces

Abstract

Nucleation of two-dimensional (2D) islands on reconstructed surfaces might involve formation of metastable nonepitaxial clusters as precursors for 2D islands. Being a thermally activated process the transformation of nonepitaxial clusters to epitaxial 2D islands might become a rate limiting step of the nucleation process at low deposition temperatures leading to substantial accumulation of the depositing atoms in nonepitaxial clusters. In the present paper, we study how slow cluster transformation influences the nucleation kinetics. For a simple model case of metastable nonepitaxial dimers and irreversible adatom incorporation into the epitaxial 2D islands, we analyze possible nucleation regimes and derive scaling relations for the density of stable 2D islands. We show that the 2D island density depends strongly on the cluster transformation rate as well as on the atomic mechanism of the dimer transformation. In particular, a steady-state nucleation regime different from the standard diffusion-mediated aggregation is possible if the transformation of a nonepitaxial dimer to the smallest epitaxial 2D island is triggered by attachment of an additional adatom. In this regime, the 2D island density obeys a nonstandard scaling $N\ensuremath{\sim}{(F/D)}^{1/4}$. Deposition conditions where this nonstandard scaling could be observed are determined.