Single-Step Synthesis of Cobalt Sulfide Nanowires Encapsulated in Carbon Nanotubes

摘要

We describe the single-step synthesis of Co_9S_8 nanowires encapsulated in carbon nanotubes (CNTs) from a dimethyl sulfide precursor, using a simple chemical vapor deposition method. The optimum dimethyl sulfide vapor concentration for the production of Co_9S_8 nanowires-filled CNTs is around 1.26-1.47%. The carbon nanotubes/Co_9S_8 nanowires were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction measurements, and energy dispersive X-ray spectroscopy. Transmission electron microscopy shows that the nanowires consist of well crystallized Co_9S_8 cores which are completely encapsulated by the sheath-like carbon nanotubes. The encapsulated Co_9S_8 nanowires are single-crystalline, and their lengths are about 10 μm with their [1,-1,0] direction parallel to the axis of the CNTs. Thorough investigation manifests that the filling of the Co_9S_8 nanowires can be ascribed to the volume increase which was induced by a phase transition from cobalt to cobalt sulfide combined with the in situ extruding action of carbon nanotubes as nanomolds. A detailed filling mechanism is proposed.