Nucleation Kinetics on Inhomogeneous Substrates: Al/Au(111)

Abstract

We report a quantitative atomic scale study of nucleation kinetics on an inhomogeneous substrate. Our model system, $\mathrm{Al}/\mathrm{Au}(111)\ensuremath{-}(\sqrt{3}\ifmmode\times\else\texttimes\fi{}22)$, reveals a distinct nucleation transition due to the repulsive nature of surface dislocations. Whereas for $T<200\mathrm{K}$ Al adatoms are confined to quasipseudomorphic stacking areas experiencing a very small diffusion barrier $(30\ifmmode\pm\else\textpm\fi{}5\mathrm{meV})$, at $T>200\mathrm{K}$ surface dislocations, representing repulsive barriers of $\ensuremath{\Delta}E\ensuremath{\approx}560\mathrm{meV}$, can be surmounted. The results illustrate the significance of surface dislocations as repulsive line defects in nucleation and growth.