Influence of quantum confinement on the electronic structure of the transition metal sulfide TS₂

Bulk MoS₂, a prototypical layered transition-metal dichalcogenide, is an indirect band gap semiconductor. Reducing its slab thickness to a monolayer, MoS₂ undergoes a transition to the direct band semiconductor. We support this experimental observation by first-principle calculations and show that quantum confinement in layered d-electron dichalcogenides results in tuning the electronic structure. We further studied the properties of related TS₂ nanolayers (T= W, Nb, Re) and show that the isotopological WS₂ exhibits similar electronic properties, while NbS₂ and ReS₂ remain metallic independent of the slab thickness.