Single- to Triple-Wall WS2 Nanotubes Obtained by High-Power Plasma Ablation of WS2 Multiwall Nanotubes

Abstract

The synthesis of inorganic nanotubes (INT) from layered compounds of a small size (<10 nm in diameter) and number of layers (<4) is not a trivial task. Calculations based on density functional tight-binding theory (DFTB) predict that under highly exergonic conditions, the reaction could be driven into a “window” of (meta-) stability, where 1–3-layer nanotubes will be formed. Indeed, in this study, single- to triple-wall WS2 nanotubes with a diameter of 3–7 nm and a length of 20–100 nm were produced by high-power plasma irradiation of multiwall WS2 nanotubes. As target materials, plane crystals (2H), quasi spherical nanoparticles (IF) and multiwall, 20–30 layers, WS2 nanotubes were assessed. Surprisingly, only INT-WS2 treated by plasma resulted in very small, and of a few layers, “daughter” nanotubules. The daughter nanotubes occur mostly attached to the outer surface of the predecessor, i.e., the multiwall “mother” nanotubes. They appear having either a common growth axis with the multiwall nanotube or tilted by approximately 30° or 60° with respect to its axis. This suggests that the daughter nanotubes are generated by exfoliation along specific crystallographic directions. A growth mechanism for the daughter nanotubes is proposed. High resolution transmission and scanning electron microscopy (HRTEM/HRSEM) analyses revealed the distinctive nanoscale structures and helped elucidating their growth mechanism.