The energy gap of pristine silicon clusters

Abstract

Studies of the fundamental energy gap of pristine silicon clusters have been performed using STM and STS. Clusters with sizes between 2.5 and 40 Å are studied. The size dependence of the gap is determined. For particles below 15 Å, gaps up to 450 meV are found. Larger particles exhibit zero gaps. The results are explained in terms of a transformation from diamond to compact structure occurring at 15 Å (∼44 atoms per cluster). For clusters with diamond structure the surface dangling bond density is high leading to electronic states filling the energy gap. On the other hand, the compact arrangement of the smaller clusters tends to eliminate dangling bonds. Therefore, finite-gap values are observed for clusters with less than ∼44 atoms.