MoS$_2$ flake as a van der Waals homostructure: luminescence properties and optical anisotropy

TL;DR

This study reveals that multilayer MoS₂ flakes form van der Waals homostructures with unique luminescence and optical anisotropy, including polarization conversion, due to their layered architecture and excitonic properties.

Contribution

It introduces the concept of MoS₂ flakes as van der Waals homostructures with distinct luminescence and anisotropic optical behavior, highlighting their structural and excitonic features.

Findings

Multilayer MoS₂ flakes form van der Waals homostructures with a bulk core and surface monolayers.

The architecture causes specific luminescence features influenced by exciton resonances.

Strong optical anisotropy and polarization conversion are observed in these flakes.

Abstract

We investigated multilayer plates made by exfoliation from a high-quality MoS$_2$ crystal and reveal that they represent a new object - van der Waals homostructure consisting of a bulk core and a few detached monolayers on its surface. This architecture comprising elements with different electron band structure leads to specific luminescence, when the broad emission band from the core is cut by the absorption peaks of strong exciton resonances in the surface monolayers. The exfoliated flakes exhibit strong optical anisotropy. We have 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 the pronounced resonance contribution is explained by the polarization anisotropy of excitons localized in the stripes of dissected surface monolayers.