Design of a heterostructure peapod using magic silicon clusters

We show that the fabrication of one-dimensional Si nanostructures with tailored electronic structure and optical properties can be achieved by encapsulating magic metal-doped Si clusters in carbon nanotubes. This cannot only effectively change the properties of the so-called peapod, but also can keep the intrinsic structure of Si clusters growing in one dimension due to its confinement by the nanotube. Using density functional calculations, the minimum tube size is found to be (9,9) for encapsulating magic ${\mathrm{WSi}}_{12}$ clusters. Due to its nonspherical shape, the interaction of the magic cluster with the tube is orientation dependent. The larger atomic size of Si also forces the cluster-tube and cluster-cluster distances to be larger than those of a ${\mathrm{C}}_{60}@\mathrm{C}$ tube, resulting in a weaker interaction with the tube. The experimental optical absorption spectra are well reproduced for empty carbon nanotubes, which can be greatly changed with ${\mathrm{WSi}}_{12}$ encapsulation, thus enabling the nanoheteropeapod to have important applications in nanodevices.