Morphology, structure and growth of WS₂ nanotubes

The morphological and structural features of WS₂ nanotubes, generated from WO(x) (x≃2.7) needles, by an in-situ heating process, have been studied by electron microscopy and X-ray diffraction (XRD), in conjunction with computer simulation. The results show that these inorganic fullerene nanotubes exhibit interesting differences when compared with carbon nanotubes (CNTs). In some cases the tube tips or segments are open. Occasionally the tube walls may be uneven. The sulfur distribution within the tubes is uniform, except for the edge layers which appear to contain less sulfur. Defects are often observed, particularly in the outer shells, which may be due to defective encapsulated WO(x) phases. Octagonal and square-like defects appear to be associated with the closure of tube caps. Electron diffraction (ED) reveals that nearly half of the non-helical WS₂ nanotubes are of the armchair-type. A mechanism has been proposed to account for the extended inorganic nanotube growth.