Filling Carbon Nanotubes with Co9S8 Nanowires through in Situ Catalyst Transition and Extrusion

We describe the synthesis of novel Co 9 S 8 -nanowire-filled carbon nanotubes (CNTs) by a simple method involving the pyrolysis of thiophene on cobalt catalyst in a conventional chemical vapor decomposition system. The encapsulated Co 9 S 8 nanowires are single-crystalline, and their lengths are about 10 μm with their [110] direction parallel to the axis of the CNTs. Detailed investigation suggests that the filling of the Co 9 S 8 nanowires results from the volume increase induced by a phase transition from cobalt to cobalt sulfide together with the in situ extruding action of CNTs as nanomolds. A new filling mechanism is thus found and proposed.