The electronic structure and especially the band gap of Si n clusters (n = 3-45 atoms) is studied by photoelectron spectroscopy. Contrary to expectations of quantum conf nement, almost all clusters studied here have a band gap smaller than that of crystalline Si or even display a continuous (metallic) density of states. We attribute this to covalent bond formation analogous 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 particular clusters.

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