Revealing the Grain Boundary Formation Mechanism and Kinetics during Polycrystalline MoS₂ Growth

Controllable synthesis of MoS₂ with desired grain morphology via chemical vapor deposition (CVD) or physical vapor deposition (PVD) remains a challenge. Hence, it is important to understand polycrystalline growth of MoS₂ and further provide guidelines for its CVD/PVD growth. Here, we formulate a kinetic Monte Carlo (kMC) model aiming at predicting the grain boundary (GB) formation in the CVD/PVD growth of polycrystalline MoS₂. In the kMC model, the grain growth is via kink nucleation and propagation, whose energetic parameters and initial nucleus details are either from first-principles calculations or from experiments. Using the kMC model, we perform extensive simulations to predict the GB formation by using two, three, four, and five initial nuclei and compare the simulation results with previous experimental results. The obtained GB morphologies are in an excellent agreement with those experimental results. These agreements suggest that the proposed kMC model can correctly capture the mechanism and kinetics of GB formation. In particular, we reveal that the formation of smooth/rough GB is dictated by the two growth vectors for the kink propagation at the two associated grain edges, which is validated by our high-resolution scanning transmission electron microscopy images for PVD growth of MoS₂ grains. Besides, we have made predictions beyond reproducing experimental observations, including the growth with artificially designed nuclei, the morphology transformation by tuning the Mo and S sources, and the formation of high-quality single-crystalline monolayer MoS₂ by using single-crystalline substrates with vicinal steps. Our kMC model may serve as a powerful predictive tool for the CVD/PVD growth of monolayer MoS₂ with desired GB configurations.