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. Editor's summary: A two-dimensional (2D) amorphous structure forms during the initial nucleation of molybdenum disulfide (MoS2) during chemical vapor deposition. Ye et al. used environmental transmission electron microscopy to follow MoS2 growth on a MoO2(210) crystal surface. Amorphous clusters transformed into amorphous 2D layered "embryos," which then formed crystalline nuclei that merged through oriented attachment. Molecular dynamics simulations helped account for the amorphous clusters needing to exceed a critical size before forming the 2D embryos.—Phil Szuromi [ABSTRACT FROM AUTHOR]