Solid–Vapor Reaction Growth of Transition-Metal Dichalcogenide Monolayers

Two-dimensional (2D) layered semiconducting transition-metal dichalcogenides (TMDCs) are promising candidates for next-generation ultrathin, flexible, and transparent electronics. Chemical vapor deposition (CVD) is a promising method for their controllable, scalable synthesis but the growth mechanism is poorly understood. Herein, we present systematic studies to understand the CVD growth mechanism of monolayer MoSe₂, showing reaction pathways for growth from solid and vapor precursors. Examination of metastable nanoparticles deposited on the substrate during growth shows intermediate growth stages and conversion of non-stoichiometric nanoparticles into stoichiometric 2D MoSe₂monolayers. The growth steps involve the evaporation and reduction of MoO₃solid precursors to sub-oxides and stepwise reactions with Se vapor to finally form MoSe₂. The experimental results and proposed model were corroborated by ab initio Car–Parrinello molecular dynamics studies.