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 the method of transforming or stabilizing it has not been established. This paper demonstrates a method of 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.