(Invited) Exploring Exciton Physics in Liquid-Exfoliated 2D Materials

Abstract

Transition metal dichalcogenides (TMDSs) are a diverse source of semiconducting 2D materials interesting for a number of application areas. Group VI-TMDs are direct bandgap semiconductors in the monolayer form making them attractive in optoelectronics due the possibility of efficient light emission. Their optical properties are dominated by tightly bound excitons with typical binding energies of 100s of meV – significantly larger than in bulk materials or traditional inorganic semiconductors. The physics of these excitons is of both fundamental interest and importance for exploiting these properties in applications and has been explored by linear and nonlinear optical techniques typically on micromechanically cleaved nanosheets. In this talk I will review our progress on investigating the exciton physics of layered materials exfoliated in the liquid phase. Liquid phase exfoliation has become a popular technique to obtain nanosheets in the form of colloidally stable dispersions suitable for solution processing. It’s an extremely versatile technique that can be applied to a whole host of layered crystals. While dispersions of nanosheets are usually polydisperse containing broad distributions of lateral sizes and thicknesses, they can nonetheless be used to study fundamental physical properties once the distributions are quantified by statistical microscopy. The advantage of the technique is the broad applicability and characterisation of an ensemble eliminating potential variations across different nanosheets. In addition, environmental effects can be conveniently studied by exchanging the liquid environment.