The electronic structure and especially the band gap of Sin clusters (n = 3 to 45 atoms) was studied by photo-electron spectroscopy. Contrary to expectations of quantum confinement, almost all clusters studied here had a band gap smaller than that of crystalline Si or even displayed a continuous (metallic) density of states. This was attributed to a covalent bond formation which was analogous to the reconstructions observed on single-crystal surfaces. For Si30 and Si33, a gap size of 0.6eV (0.4eV) was observed; supporting the prediction of stable spherically symmetrical structures for these particular clusters.

The Electronic Structure and the Band Gap of Nano-Sized Si Particles - Competition between Quantum Confinement and Surface Reconstruction. M.Maus, G.Ganteför, W.Eberhardt: Applied Physics A, 2000, 70[5], 535-9