MoS$_2$ bulk/monolayers van der Waals homostructures: luminescence properties and optical anisotropy

We investigated multilayer plates made by exfoliation from a high-quality MoS$_2$ crystal and found thatthey represent a van der Waals homostructure consisting of a bulk core and a few monolayers on itssurface. This architecture comprising elements with different electron band structure leads to specificluminescence, when the broad emission band from the core is cut by the absorption peaks of strongexciton resonances in the monolayers. The exfoliated flakes exhibit strong optical anisotropy. Wehave observed a conversion of normally incident light polarization to 15~% in transmission geometry.This background effect is due to fluctuations of the c axis relative to the normal, whereas thepronounced resonance contribution is explained by the polarization anisotropy of excitons localizedin monolayer bands.