On the synthesis of WS2 nanotubes: reaction mechanism revelation by in-situ scanning and ex-situ transmission electron microscopy

This study provides a comprehensive understanding of the WS2 nanotube synthesis mechanism by conducting in-situ SEM and ex-situ TEM analyses of the sulfidation reaction of W18O49 nanowhiskers. The formation of WS2 nanotubes initiates with the rapid passivation of the reactive tungsten suboxide surface, followed by the evaporation of the oxide core and pressure buildup inside the nascent nanotube. The compactness and defectiveness of the initial passivation layer, gas pressure differences, and the structure of the W18O49 nanowhisker play crucial roles in determining the morphology of the final WS2 nanotubes. Additionally, this work elucidates the cause of open or closed nanotube tips based on gas pressure conditions. The combination of in-situ SEM technology and ex-situ sequential TEM analysis emerges as a robust and reliable methodology for investigating high-temperature heterogeneous reactions.