Atomically resolved two-dimensional amorphous nuclei formed during MoS₂ chemical vapor deposition

Control over the nucleation and growth of two-dimensional (2D) materials is essential for their scalable manufacturing. We report in situ atomic-scale observations of molybdenum disulfide (MoS₂) nucleation and growth through chemical vapor deposition (CVD) using environmental transmission electron microscopy. Coupled with molecular dynamics simulations, our observations reveal the formation of a 2D amorphous structure at the initial nucleation stage, which undergoes an in-plane structural ordering transition into a crystalline nucleus once a critical size is reached. We further captured nuclei merging and oriented attachment processes in the early growth stage, which likely contributed to 2D single-crystal fabrication. These findings unveil the atomistic structural evolution in MoS₂ nucleation and growth under CVD condition, providing mechanistic insight for the controlled synthesis of high-quality 2D crystals and informing broader strategies for covalently bonded material systems.