Moiré superstructure-dependent growth mechanisms of transition metal dichalcogenides on the Au(111) surface

A thorough understanding of growth mechanisms is essential for the controllable synthesis of transition metal dichalcogenides (TMDCs), which is crucial for their various applications. This study systematically investigates the role of the substrate in governing the edge reconstructions and the growth behaviors of MoS₂ during the CVD process under different chemical environments. Thermodynamic analysis demonstrates that Mo-terminated zigzag (ZZ-Mo) edges are always energetically preferred for freestanding MoS₂, while on the Au(111) surface, MoS₂ domains are predominantly terminated by either ZZ-Mo edges or S-terminated zigzag (ZZ-S) edges, depending on the chemical environment. Further considering the kinetic growth process, it is the moiré superstructure-dependent growth behavior that critically determines the morphology of MoS₂ domains. Under a near-equilibrium state, the MoS₂ domain evolves from a standard triangular shape with pristine ZZ-S edges to a hexagon and finally to an S-passivated ZZ-Mo triangle as the S content increases. Increasing the growth driving force is beneficial for accelerating this morphological transition. In addition, orientation analysis reveals that substrate step engineering is crucial for breaking the degeneracy between antiparallel MoS₂ domains. Our results reveal the moiré superstructure-dependent growth mechanisms of TMDCs and exhibit excellent agreement with existing experimental observations. This research establishes a theoretical framework for understanding the growth and thereby achieving the controllable synthesis of TMDCs.