Real-Time Observation for MoS₂ Growth Kinetics and Mechanism Promoted by the Na Droplet

While the molten salt-catalyzed chemical vapor deposition (CVD) technique is recognized for its effectiveness in producing large-area transition metal chalcogenides, understanding their growth mechanisms involving alkali metals remains a challenge. Here, we investigate the kinetics and mechanism of sodium-catalyzed molybdenum disulfide (MoS₂) growth and etching through image analysis conducted using an integrated CVD microscope. Sodium droplets, agglomerated via the thermal decomposition of the sodium cholate dispersant, catalyze the precipitation of supersaturated MoS₂ laminates and induce growth despite fragmentation during this process. Triangular MoS₂ crystals display a distinct self-exhausting exponential behavior and slow growth of thermodynamically favorable crystallographic faces, exhibiting a sulfur-dominant pressure. The growth and etching processes are facilitated by the scooting of sodium droplets along grain edges, displaying comparable rates. Leveraging these kinetics makes it possible to engineer atypical MoS₂ shapes. This combined microscope not only enhances the understanding of growth mechanisms but also contributes to the facile development of next-generation nanomaterials.