Band-gap transition induced by interlayer van der Waals interaction in MoS2

We have investigated the electronic structures of single- and double-layered MoS2, composing of heterojunction structures such as graphene, MoS2, and SiO2 and MoS2 and SiO2, using scanning photoelectron microscopy. Negative shifts of both core levels and valence bands toward the Fermi energy have been observed. In connection with first-principles calculations, we have confirmed that the direct gap of single-layer MoS2 is changed to an indirect gap by stacking additional layers via van der Waals interlayer interactions.