Influence of monolayer MoS₂ grain boundaries on MoS₂ cluster nucleation during layer-by-layer growth of bilayer MoS₂

Bilayer transition-metal dichalcogenides (TMDs) have promising applications in photoelectronic devices due to their unique physical and chemical properties. Grain boundaries (GBs) are an inevitable defect in the synthesis of TMDs, which will affect the nucleation behavior of the next-layer material, thereby altering the materials’ properties and their applications as devices. However, it remains unclear how the GBs of monolayer MoS₂ regulate the nucleation of the next-layer MoS₂ clusters. Here, we present a statistical analysis of the crystallographic orientation of MoS₂ grown on GBs via chemical vapor deposition, and calculate the energy landscape between MoS₂ cluster molecule and underlying MoS₂ containing GBs. Our results reveal that the interlayer energy strongly depends on the size, termination edge type and nucleation position of MoS₂ cluster. Additionally, the regulatory effect of GBs on MoS₂ clusters is notably effective within ∼4 Å but negligible outside. Theoretically, the most favorable stacking configurations at GBs are bilayer MoS₂ with 0° and small deflection angles (defined as the angle deviating from the regulation of perfect lattice), consistent with our experimental results. Our work clarifies the nucleation mechanism of MoS₂ on GBs, which is scientifically important for optimizing the controlled growth of TMDs.