Effects of short-range repulsive barriers on island nucleation

A variety of effects such as strain and surfactants can lead to attachment barriers in thin-film growth. While several studies of the effects of attachment barriers on submonolayer growth have been carried out, the emphasis has been on rate-equations which do not take into account island geometry or coalescence and are primarily applicable to point-islands. Here we present the results of kinetic Monte Carlo simulations for the case of extended 2D islands with critical island-size i = 1 which were carried out to determine the dependence of the exponent χ (describing the dependence of the peak island density on deposition rate) on barrier strength and ratio R = D/F of the monomer hopping rate D to deposition rate F. In particular, we have studied two different cases, one with a barrier to island nucleation and attachment as well as the case with an island attachment barrier but no nucleation barrier. Our results indicate that in both cases - and in contrast to the case of no barrier for which χ is equal to 1/3 - the asymptotic (large R) value of χ increases continuously with barrier strength, reaching a value close to ½ in the limit of a very strong barrier and very large R. The effects of attachment barriers on island morphology and coalescence will also be discussed.