Reversible H-T′ phase transition in monolayer molybdenum disulfide via electron beam assisted solid state lithiation/delithiation

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) possess a variety of polymorphs that exhibit distinctive atomic and electronic structures and the consequent material properties. Hence, exploiting the dynamics of phase transition between different polymorphs will lay a foundation toward controlled phase engineering based applications. In this Letter, we reported a solid-state approach to realize the H to T′ transition in monolayer molybdenum disulfide in situ inside a transmission electron microscope. The release of lithium ions and the subsequent lithiation were driven by energetic electron beam irradiation, both of which in turn triggered the H to T′ phase transition of the object monolayer MoS2. The as-formed T′ phase domains showed a random nucleation behavior. Interestingly, the reverse process, i.e., T′ back to H phase transition, caused by prolonged e-beam illumination, was also captured in situ. During both phase transformation processes, i.e., H → T′ and T′ → H, we did not observe any large area T phase existing in monolayer MoS2. Our results will be instructive to elucidate the microscopic mechanisms of the phase transition and should also be extendable to other 2D TMD materials.