The Effect of Nickel on MoS 2 Growth Revealed with in Situ Transmission Electron Microscopy.

MoS ₂ has important applications in (electro)catalysis and as a semiconductor for electronic devices. Other chemical species are commonly added to MoS ₂ to increase catalytic activity or to alter electronic properties through substitutional or adsorption-based doping. While groundbreaking work has been devoted to determining the atomic-scale structure of MoS ₂ and other layered transition-metal dichalcogenides (TMDCs), there is a lack of understanding of the dynamic processes that govern the evolution of these materials during synthesis. Here, in situ transmission electron microscopy (TEM) heating, in combination with larger length scale ex situ experiments, is used to investigate the effects of added Ni on the growth of MoS ₂ during the thermolysis of the solid-state (NH ₄ ) ₂ MoS ₄ precursor. Low concentrations of Ni are observed to cause significant differences in the MoS ₂ crystallization and growth process, leading to an increase in MoS ₂ crystal size. This is likely a result of the altered mobility of interfaces between crystals during growth. These findings demonstrate the important role of additional elements in controlling the evolution of TMDCs during synthesis, which should be considered when designing these materials for a variety of applications.