The Effect of Nickel on MoS₂ Growth Revealed with in Situ Transmission Electron Microscopy

MoS₂ has important applications in (electro)catalysis and as a semiconductor for electronic devices. Other chemical species are commonly added to MoS₂ 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 MoS₂ 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 MoS₂ during the thermolysis of the solid-state (NH₄)₂MoS₄ precursor. Low concentrations of Ni are observed to cause significant differences in the MoS₂ crystallization and growth process, leading to an increase in MoS₂ 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.