Environment-dependent and anion vacancy-controlled reversible phase transition of MoS2 synthesized by chemical vapor deposition

Abstract: The crucial role of anion vacancies on the phase stability of synthetic metal chalcogenides was elucidated by demonstrating the environment-dependent, reversible phase transition (2H ↔ 1T/1T’) of the MoS2 films synthesized by the chemical vapor deposition (CVD). The origins for the S vacancy-controlled phase transition of the synthetic MoS2 films were supported by various transmission electron microscopy (TEM) studies and density functional theory calculations. In a high vacuum condition, transition to a metastable 1T/1T’ phase was induced by weak electron irradiation during TEM observation and explained by the detachment of molecules chemisorbed on the S vacancy sites and the subsequent electron delocalization (charge transfer) process. In addition, a spontaneous backward transition to a 2H phase could be triggered by exposing the sample to air, which induced electron localization by re-adsorption of ambient molecules on the S vacancy sites.