Predictions of novel nanostructures of silicon by metal encapsulation

Recent studies using ab initio total energy calculations have shown exciting possibilities of developing novel metal encapsulated caged clusters of silicon with fullerene-like, Frank–Kasper and other polyhedral structures. In contrast to carbon for which empty cage fullerene structures are stable with 20 or more atoms, 10–16 atom silicon cage structures are stabilized by a guest metal atom. These nanoclusters are predicted to exhibit luminescence in the visible range and could find applications in biological systems, optoelectronics, and as tagging material. The Raman and infrared spectra have been calculated and they could help in the experimental identification of the structures. Interaction of these clusters with metal as well as oxygen or hydrogen atoms show that the fullerene structure is stable. Also the interaction between clusters themselves is weak and the ionization potentials, large. These properties make them attractive for cluster assembled materials such as nanowires, nanotubes, and other 2 and 3D structures. Studies on hydrogen interaction have led to the predictions of empty center hydrogenated silicon fullerenes Si_nH_n with large HOMO–LUMO gaps. These could further be doped endohedrally or exohedrally to produce novel silicon fullerenes with a variety of properties opening new ways of using silicon for diverse applications.