Phase transition in MoX₂ (X = S, Se, Te) monolayers with hydrogenation

Surface functionalization of two-dimensional monolayers can produce materials with different structural and electronic properties as compared to their pure counterparts. The lowest energy phase for molybdenum (Mo) based transition metal dichalcogenides is the semiconducting hexagonal H phase. However, the alternative T phase with Mo atoms in octahedral coordination and the distorted version of the T phase (T') can be stabilized by intercalation, chemical doping, and charge mediation. In this work, we use density functional theory calculations to demonstrate that H to T phase transition can be achieved in MoX₂ monolayer with hydrogenation. We find that the phase stability of the T phase increases as a function of hydrogenation coverage. This phase transition results in the semiconductor to metallic transition in these monolayers. Our results suggest that these MoX₂ monolayers with controllable structural and electronic properties can find applications in catalysts and nanodevices.