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.