Computational exploration of novel silicon nanostructures

Discovery of novel Si nanostructures would open up a new avenue for science and technology as the discoveries of C₆₀ and carbon nanotubes did. With this expectation, we have explored novel Si nanostructures by combining empirical moleculardynamics simulations and structure optimizations with the density functional theory^1,2,3,4. Our molecular-dynamics simulations demonstrate (1) an icosahedral Si nanodot forms by freezing a droplet in vacuum¹, (2) Si-fullerene-linked nanowires, such as Si_16- and Si₂₀-linked nanowires, form by freezing liquid Si inside carbon nanotubes², and (3) a polyicosahedral Si nanowire forms by freezing liquid Si inside a cylindrical nanopore³. The unique cage structure of the polyicosahedral Si nanowire allows us to tune the electronic properties by encapsulating guest atoms into its cages. Our density functional theory calculations reveal that a semiconducting hydrogen-terminated polyicosahedral Si nanowire becomes metallic by the sodium and iodine doping⁴.