Continuous and correlated nucleation during nonstandard island growth at Ag/Si(111)-7x7 heteroepitaxy

TL;DR

This study combines experiments and simulations to understand how Ag atoms nucleate and grow on Si(111)-7x7, revealing correlated nucleation and specific growth mechanisms during heteroepitaxy.

Contribution

It introduces a coarse-grained kinetic Monte Carlo model that captures correlated nucleation and provides new parameters for Ag atom behavior in heteroepitaxial growth.

Findings

Small islands dominate growth at all stages.

Growth proceeds via continuous nucleation and coalescence.

Model accurately fits experimental data on HUC occupation.

Abstract

We present a combined experimental and theoretical study of submonolayer heteroepitaxial growth of Ag on Si(111)-7x7 at temperatures from 420 K to 550 K when Ag atoms can easily diffuse on the surface and the reconstruction 7x7 remains stable. STM measurements for coverages from 0.05 ML to 0.6 ML show that there is an excess of smallest islands (each of them fills up just one half-unit cell - HUC) in all stages of growth. Formation of 2D wetting layer proceeds by continuous nucleation of the smallest islands in the proximity of larger 2D islands (extended over several HUCs) and following coalescence with them. Such a growth scenario is verified by kinetic Monte Carlo simulation which uses a coarse-grained model based on a limited capacity of HUC and a mechanism which increases nucleation probability in a neighbourhood of already saturated HUCs (correlated nucleation). The model provides a good fit for experimental dependences of the relative number of Ag-occupied HUCs and the preference in occupation of faulted HUCs on temperature and amount of deposited Ag. Parameters obtained for the hopping of Ag adatoms between HUCs agree with those reported earlier for initial stages of growth. The model provides two new parameters - maximum number of Ag atoms inside HUC, and on HUC boundary.