Oxidation and hydrogenation of monolayer MoS₂ with compositing agent under environmental exposure: The ReaxFF Mo/Ti/Au/O/S/H force field development and applications

An atomistic modeling tool is essential to an in-depth understanding upon surface reactions of transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS₂), with the presence of compositing agents, including Ti and Au, under different environmental exposures. We report a new ReaxFF reactive force field parameter set for Mo, Ti, Au, O, S, and H interactions. We apply the force field in a series of molecular dynamics (MD) simulations to unravel the impact of the Ti dopant on the oxidation/hydrogenation behaviors of MoS₂ surface. The simulation results reveal that, in the absence of Ti clusters, the MoS₂ surface is ruptured and oxidized at elevated temperatures through a process of adsorption followed by dissociation of the O₂ molecules on the MoS₂ surface during the temperature ramp. When the MoS₂ surface is exposed to H₂O molecules, surface hydrogenation is most favored, followed by oxidation, then hydroxylation. The introduction of Ti clusters to the systems mitigates the oxidation/hydrogenation of MoS₂ at a low or intermediate temperature by capturing the O₂/H₂O molecules and locking the O/H-related radicals inside the clusters. However, OH⁻ and H₃O⁺ are emitted from the Ti clusters in the H₂O environment as temperature rises, and the accelerating hydrogenation of MoS₂ is consequently observed at an ultra-high temperature. These findings indicate an important but complex role of Ti dopants in mitigating the oxidation and hydrogenation of MoS₂ under different environmental exposures. The possible mechanisms of oxidation and hydrogenation revealed by MD simulations can give an insight to the design of oxidation resistant TMDs and can be useful to the optical, electronic, magnetic, catalytic, and energy harvesting industries.