Al nanocluster arrays onSi(111)−7×7surfaces: Formation process and interactions among clusters

Abstract

By means of variable-temperature scanning tunneling microscopy, we have investigated systematically the formation process of Al magic cluster arrays on the $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface at high temperature in situ. It was found that the magic clusters form only when the Al coverage is over a critical value, $\ensuremath{\sim}0.08\ifmmode\pm\else\textpm\fi{}0.015$ ML. These clusters occupy preferentially on the faulted-half-unit cells of the $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface, but this preference is coverage dependent. By analyzing systematically the spatial distribution of magic clusters below the saturation coverage, an attractive interaction between clusters was found, which prevents a triangular ordering of the nanocluster array.