Gas-Phase "Prehistory" and Molecular Precursors in Monolayer Metal Dichalcogenides Synthesis: The Case of MoS₂.

Abstract

Two-dimensional MoS₂ is one of the most promising materials for nanoelectronics due to its semiconducting nature and plethora of extraordinary properties. The main method for mass production of large-scale, high-quality MoS₂ monolayers is chemical vapor deposition (CVD). Yet, the details of the chemistry occurring during the synthesis remain largely unknown, hindering process optimization. Combining <i>ab initio</i> molecular dynamics (AIMD) simulations and first-principles calculations allows us to explore the complete processes of MoS₂ monolayer growth at the atomic level. We find that solid MoO₃ precursor sublimates forming ringlike molecules, such as Mo₃O₉, which can later be regarded as gas-phase Mo-carrier reactants, undergoing sulfurization in three main stages: ring opening, chain breaking as the rate-limiting step, and further sulfurization. The fully sulfurized MoS₆ molecule emerges as an immediate gas precursor to the crystal growth, as it reacts to join the MoS₂-layer edge, with the release of a S₄ molecule. Our comprehensive study provides detailed insights into the microscopic reaction mechanisms of MoS₂ CVD growth and guidance for optimizing the synthesis parameters for transition metal dichalcogenides.