Morphology of multiwall WS2 nanotubes

Recent progress in the synthesis of bulk quantities of long WS2 nanotubes h as allowed them to be considered as potential candidates in various applica tions, specifically in nanotechnology. In order to evaluate their efficacy in such applications and to obtain a better insight into their growth mecha nism, morphological studies were performed both by scanning electron micros copy and transmission electron microscopy. Three types of WS2 nanotubes, a few microns in length, were found. The nanotubes denoted "thin" have a diam eter up to 30 nm and are circular; those denoted "thick" have a larger diam eter, up to 150 nm, and are often polygonal. A third kind of nanotube, bund led or fused, could be also discerned. Differences in the morphology of the nanotube caps were also observed: The majority of "thin" nanotubes exhibit a head close to hemispherical, while the "thick" ones have a peculiar 90 d egrees apex. It is argued that the two discernible morphologies are obtaine d through two distinct growth mechanisms, as discussed in the text.