Phase Engineering of 1T'-MoS₂ via Organic Enwrapment

Molybdenum disulfide (MoS₂) is a layered material known to show various phases. Most studies on it have focused on its semiconductor phase, but it is known to also have a metallic 1T' phase. This 1T' phase has also drawn attention as a quantum spin Hall phase, but the 1T' phase is metastable, and methods for transforming or stabilizing it are still challenging. This Communication demonstrates a method for effectively transforming the monolayer or the topmost layer of multilayer semiconductor MoS₂ (the 1H or 2H phase) into the 1T' phase via ultraviolet-ozone (UVO) treatment, followed by polymer enwrapment of the MoS₂ surface. UVO induces the transformation of the 1H (2H) phase into the 1T' phase, but the generated phase is unstable. The enwrapment procedure with the polymer poly-l-lysine was found to be effective in transforming the 1H (2H) phase into the 1T' phase and stabilizing it. Moreover, this procedure transformed only the topmost layer and generated a vertical 1T'/2H heterostructure in multilayer cases. This study shows the high potential of surface organic chemical procedures to control the phases in 2D transition metal dichalcogenides.