Post-Synthetic Method for Defined 1T′ Phase in Chemical Vapor Deposition-Grown Monolayer Molybdenum Disulfide

Monolayer molybdenum disulfide (MoS₂) is one of the most studied two-dimensional materials. While the thermodynamically stable and well-investigated state of monolayer MoS₂ is the semiconducting 1H phase, it can also exist in the 1T' phase, which exhibits semimetallic characteristics and topologically protected properties. However, scalable postsynthetic methods to achieve and stabilize the 1T' phase remain elusive, as monolayer MoS₂ selectively reverts to the 1H phase under thermal equilibrium. In this study, we present a strategy to induce, stabilize, and spatially define the 1T' phase in monolayer MoS₂ synthesized via chemical vapor deposition (CVD). By employing a sequential oxidation process followed by polymer enwrapment, we successfully converted CVD-grown monolayer MoS₂ from the 1H phase to the 1T' phase. Transport measurements reveal a weak gate dependence, consistent with the semimetallic nature of the 1T' phase. Our results further demonstrate that interfacial interactions with the polymer play a critical role in both facilitating the conversion and stabilization of the 1T' monolayer MoS₂. The phase conversion from 1H to 1T' induces significant structural rearrangements, leading to the formation of nanoscale wrinkles in the monolayer flake. The lateral size of the 1T' domains is estimated to be approximately 100-200 nm, suggesting that an in-plane strain of approximately 1% is introduced during the oxidation process. This strain is effectively stabilized by the polymer interface. The entire treatment is carried out under ambient conditions at room temperature, providing a simple and scalable approach to phase engineering in two-dimensional materials.