We report on the in situ heating transmission electron microscopy (TEM) study of WS2 and MoS2 nanoparticles obtained from metal–organic chemical vapor deposition (MOCVD). The general behavior of MoS2 and WS2 is similar: Round, amorphous particles in the pristine sample transform to hollow, onion-like particles upon annealing. A second type of particle with straight layers exhibits only minor changes. A significant difference between both compounds could be demonstrated in their crystallization behavior. The results of the in situ heating experiments are compared to those obtained from an ex situ annealing process under Ar.
The synthesis of WS 2 onion-like nanoparticles by means of a high-temperature metal-organic chemical vapor deposition (MOCVD) process starting from W(CO) 6 and elemental sulfur is reported. The reaction can be carried out as a single-step reaction or in a two-step process where the intermediate products, amorphous WS 2 nanoparticles, formed through the high-temperature reaction of tungsten and sulfur in the initial phase of the reaction, are isolated and converted into onion-type WS 2 nanoparticles in a separate annealing step. Analysis of the reaction product using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) combined with energy dispersive X-ray spectroscopy (EDX) allowed to optimize the reaction in such a way that filled onion-like structures are formed in a one-step reaction, whereas hollow onion-like structures are obtained by the two-step procedure. A model could be devised that allows us to rationalize the different outcome of the reactions. The MOCVD approach therefore allows a selective synthesis of open and filled fullerene-like chalcogenide nanoparticles.
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