Reactivity of Sulfur Molecules on MoO (010) Surface.

Two-dimensional and layered MoS 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 MoS monolayer on a target substrate. During CVD synthesis, sulfidation of MoO surface is a critical reaction step, which converts MoO to MoS. However, initial reaction steps for the sulfidation of MoO remain to be fully understood. Here, we report first-principles quantum molecular dynamics (QMD) simulations for the initiation dynamics of sulfidation of MoO (010) surface using S and S molecules. We found that S molecule is much more reactive on the MoO surface than S molecule. Furthermore, our QMD simulations revealed that a surface O-vacancy on the MoO 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 MoO and gas-phase sulfur precursors for CVD synthesis of MoS layers.