Laboratoire de Physique des Interfaces et des Couches Minces

CNRS - École polytechnique - Institut Polytechnique de Paris

Aromatic Silicon Nanoclusters

Written by : Holger Vach

Based on ab initio molecular dynamics simulations, we show that small nanoclusters of about 1 nm size spontaneously generated in a low-temperature silane plasma do not possess tetrahedral structures, but are ultrastable. Apparently small differences in the cluster structure result in substantial modifications in their electric, magnetic, and optical properties, without the need for any dopants. Their non-tetrahedral geometries notably lead to electron deficient bonds that introduce efficient electron delocalization that strongly resembles the one of a homogeneous electron gas leading to metallic-like bonding within a semiconductor nanocrystal. As a result, pure hydrogenated silicon clusters that form by self-assembly in a plasma reactor possess optical gaps covering most of the solar spectrum from 1.0 eV to 5.2 eV depending simply on their structure and, in turn, on their degree of electron delocalization. This feature makes them ideal candidates for future bandgap engineering not only for photovoltaics, but also for many nano-elec- tronic devices employing nothing else but silicon and hydrogen atoms.

Two-dimensional Electron Localization Function (ELF) plots in different planes for the Si19H12 nanocrystal and for benzene C6H6: (a) for benzene as a reference molecule; (b) in the top hexagon; (c) in the center hexagon; (d) in the plane between the central hexagon and the endohedral Si atom; and (e) in the plane of the endohedral Si atom of the highly-symmetric Si19H12 cluster.