Clearing the Chemistry in the Synthesis of Transition Metal Dichalcogenides

Transition metal dichalcogenides are prominent materials for nanoelectronics and nanophotonics. Chemical vapor deposition remains the most effective way for the mass production of their 2D layers with high quality. The method has continuously been improved, from conventional growth using oxides as precursors, to recently developed salt-assisted growth,¹ where alkali metal halide salts are additionally included in the synthesis. Millimeter-sized 2D MoS₂ crystals have been achieved in experiments using the salt-assisted strategy, yet the details of the chemistry occurring during the synthesis are still ambiguous. Here, we employ first-principles calculations and <i>ab initio</i> molecular dynamics simulations to reveal the entire growth process,² including the sublimation of solid precursors, the gas sulfurization reactions, and the crystal growth at the flake edge, during the chemical vapor deposition synthesis of MoS₂ monolayers. The comparisons between the conventional and salt-assisted synthesis are made and the rules for choosing the best halide salts are discussed.³ Our study should promote the understanding of the chemical vapor deposition synthesis of transition metal dichalcogenides, and facilitate the process optimization to achieve their even faster growth in experiments.<br/><br/>1. J. Zhou <i>et al.</i>, <i>Nature</i> 556, 355–359 (2018).<br/>2. J. Lei <i>et al.</i>, <i>ACS Nano</i> 15, 10525–10531 (2021).<br/>3. J. Lei <i>et al.</i>, In preparation.