A ReaxFF Force Field for 2D-WS2 and Its Interaction with Sapphire

We present a new ReaxFF reactive force field parameter set enabling large-scale computational synthesis and characterization of 2D-WS2, guided by an extensive quantum mechanical data set on both periodic and nonperiodic systems and validated against ADF-STEM experiments. This potential is designed to capture the most essential features of a WS2 thin film, such as the 2H -> 1T displacive phase transition, S-vacancy migration, and the energetics of various point and line defects, e.g., ripplocations in a WS2 monolayer, thus enabling cost-effective simulations supporting phase and defect engineering of 2D-WS2. Additionally, the new ReaxFF description accurately describes the nucleation of a finite 1T phase on the 2H basal plane or edges, the rotational and translational grain boundaries, and the coupled effect of chemical potential and edge stability on the formation of S- and W-oriented grain boundaries. Because the epitaxial relationship between the substrate and 2D flakes plays a key role in controlling the growth direction and thus the crystal quality of a 2D film, this potential is trained further for the WS2/sapphire interface and therefore can provide valuable insights into the morphological changes observed in a coalesced WS2 grown film on sapphire.

Automated summary

The study introduces a new ReaxFF parameter set for large-scale computational synthesis and characterization of 2D-WS2, designed to capture essential features of thin films and support phase and defect engineering. The method also accurately describes the formation of grain boundaries and the influence of chemical potential on their stability.