The electronic structure and the band gap of nano-sized Si particles: competition between quantum confinement and surface reconstruction

The electronic structure and especially the band gap of Si-n clusters (n = 3-45 atoms) is studied by photoelectron spectroscopy. Contrary to expectati ons of quantum confinement, almost all clusters studied here have a band ga p smaller than that of crystalline Si or even display a continuous (metalli c) density of states. We attribute this to covalent bond formation analogou s to the reconstructions observed on single-crystal surfaces. Additionally, for Si-30 and Si-33 a gap size of 0.6 eV (0.4 eV) is observed, supporting the prediction of stable, spherically symmetric structures of these particu lar clusters.