Single Walled BiI(3) Nanotubes Encapsulated within Carbon Nanotubes

Inorganic nanotubes are morphological counterparts of carbon nanotubes (CNTs). Yet, only graphene-like BN layer has been readily organized into single walled nanotubes so far. In this study, we present a simple route to obtain inorganic single walled nanotubes - a novel ultrathin morphology for bismuth iodide (BiI(3)), embedded within CNTs. The synthesis involves the capillary filling of BiI(3) into CNT, which acts as a nanotemplate, by annealing the BiI(3)-CNT mixture above the melting point of BiI(3). Aberration corrected scanning/transmission electron microscopy is used in characterizing the novel morphology of BiI(3). A critical diameter which enables the formation of BiI(3) nanotubes, against BiI(3) nanorods is identified. The relative stability of these phases is investigated with the density functional theory calculations. Remarkably, the calculations reveal that the single walled BiI(3) nanotubes are semiconductors with a direct band gap, which remain stable even without the host CNTs.