Atomistic reaction mechanism of CVD grown MoS₂ through MoO₃ and H₂S precursors

Chemical vapor deposition (CVD) through sulfidation of MoO₃ is one of the most important synthesis techniques to obtain large-scale and high-quality two-dimensional (2D) MoS₂. Recently, H₂S precursor is being used in the CVD technique to synthesize 2D MoS₂. Although several studies have been carried out to examine the mechanism of MoS₂ growth in the presence of sulfur and MoO₃ precursors, the growth of MoS₂ in the presence of H₂S precursor has largely remained unknown. In this study, we present a Reactive molecular dynamics (RMD) simulation to investigate the reaction mechanism of MoS₂ from MoO₃ and H₂S precursors. The intermediate molecules formation, the reason behind those formations, and the surface compositions of MoO_xS_yH_z during the initial steps of CVD have all been quantified. Surprisingly, a sudden separation of sulfur atoms from the surface was observed in the H₂S precursor system due to the substantial oxygen evolution after 1660 K. The sulfur detachments and oxygen evolution from the surface were found to have a linear relationship. In addition, the intermediate molecules and surface bonds of MoS₂ synthesized by MoO₃ and H₂S precursors were compared to those of a system using S₂ and MoO₃ precursors. The most stable subsidiary formation from the H₂S precursor was found to be H₂O, whereas in case of S₂ precursor it was SO. These results provide a valuable insight in the formation of large-scale and high-quality 2D MoS₂ by the CVD technique.