Reactive Co magic cluster formation onSi(111)−(7×7)

Abstract

Cobalt-induced magic clusters have been grown on $\mathrm{Si}(111)\text{\ensuremath{-}}(7\ifmmode\times\else\texttimes\fi{}7)$. In situ scanning tunneling microscopy studies show that the clusters are off-center in the $7\ifmmode\times\else\texttimes\fi{}7$ half-unit-cell breaking the local threefold symmetry, and thereby distinguishing this system from other group-III magic clusters. Another unique feature of these clusters is that they are accompanied by voids created by two missing adatoms. Supported by first-principles total energy calculations, we propose a model to explain the atomic structure and formation mechanism of these clusters. The reactive nature of Co leads to the liberation of substrate Si atoms which eventually bond with Co to form the clusters.