WS2 and MoS2 Microtubes, Nanotubes and Ropes: Structure and Growth
M. Remskar1, Z. Skraba1, R. Sanjines2, and F. Levy2MoS2 and WS2 cylindrical crystals of similar geometry to carbon nanotubes have been grown by chemical transport reaction. Microtubes with observed diameters up to 20 microns and lengths of several millimetres grow together with nanotubes and strongly undulated plate-like crystal flakes. The presence of plate-like crystals is essential for the growth of tubes. The tubes grow by helical winding of molecular layers with the [001] basal plane perpendicular to the tube cross section. In the microtube walls the rhombohedral polytype is systematically stabilized in contrast with the hexagonal stacking present in the nanotubes or in plate-like crystals. We observed different types of MoS2 and WS2 tubes, ribbons and ropes with respect to their origin, including a self-assembly and a syntactic growth of nanotubes. A model for the origin of the undulation of thin crystal flakes is proposed. It is based on stacking mismatch. An attractive long-range interaction causing the nanotube approach is discussed. Atomically resolved surface structure is compared with the high-resolution transmission electron microscopy observations.
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