Submonolayer Epitaxy Without A Critical Nucleus

TL;DR

This paper investigates the nucleation and growth of 2D islands in epitaxial growth using Monte Carlo simulations, revealing that traditional critical island size concepts do not apply due to thermal detachment, and introduces a new indexing method based on dimer dissociation.

Contribution

It demonstrates that island stability cannot be solely defined by a critical size and proposes a new scaling approach based on dimer dissociation rates, validated with Fe/Fe(001) data.

Findings

Dimer dissociation rate ratio indexes island size distribution.

Scaling functions depend on the ratio of dissociation to capture rates.

Effective parameters match experimental Fe/Fe(001) results.

Abstract

The nucleation and growth of two--dimensional islands is studied with Monte Carlo simulations of a pair--bond solid--on--solid model of epitaxial growth. The conventional description of this problem in terms of a well--defined critical island size fails because no islands are absolutely stable against single atom detachment by thermal bond breaking. When two--bond scission is negligible, we find that the ratio of the dimer dissociation rate to the rate of adatom capture by dimers uniquely indexes both the island size distribution scaling function and the dependence of the island density on the flux and the substrate temperature. Effective pair-bond model parameters are found that yield excellent quantitative agreement with scaling functions measured for Fe/Fe(001).