Reactivity of Sulfur Molecules on MoO₃ (010) Surface

Two-dimensional and layered MoS₂ is a promising candidate for next-generation electric devices due to its unique electronic, optical, and chemical properties. Chemical vapor deposition (CVD) is the most effective way to synthesize MoS₂ monolayer on a target substrate. During CVD synthesis, sulfidation of MoO₃ surface is a critical reaction step, which converts MoO₃ to MoS₂. However, initial reaction steps for the sulfidation of MoO₃ remain to be fully understood. Here, we report first-principles quantum molecular dynamics (QMD) simulations for the initiation dynamics of sulfidation of MoO₃ (010) surface using S₂ and S₈ molecules. We found that S₂ molecule is much more reactive on the MoO₃ surface than S₈ molecule. Furthermore, our QMD simulations revealed that a surface O-vacancy on the MoO₃ surface makes the sulfidation process preferable kinetically and thermodynamically. Our work clarifies an essential role of surface defects to initiate and accelerate the reaction of MoO₃ and gas-phase sulfur precursors for CVD synthesis of MoS₂ layers.