Nanostructured silicon films obtained by neutral cluster depositions

Nanosize neutral silicon clusters produced using a laser vaporization source were analyzed in the gas phase and deposited on various substrates at room temperature in ultrahigh vacuum. Nanostructured thin films with thickness around 100 nm resulting from this nearly ballistic deposition process were subsequently characterized by several complementary electron spectroscopy techniques to investigate the electronic structure. The film properties are comparable to those of a disordered phase but different from the properties of conventional amorphous or nanoporous silicon. The specific features observed in the Si-cluster assembled films cannot be simply interpreted on the basis of quantum confinement effects and are rather attributed to the presence of odd-membered rings in the incident-free cluster structure. Some Si-cluster geometries in the subnanometric size range are proposed and discussed on the basis of the experimental results and a tight binding scheme.