Unique excitonic effects in tungsten disulphide monolayers on two-layer graphene

TL;DR

This study demonstrates that the excitonic properties and photoluminescence of WS2 monolayers can be significantly modulated by the number of graphene layers in the substrate, emphasizing substrate engineering in 2D heterostructures.

Contribution

It reveals how the number of graphene layers influences charge transfer and excitonic effects in WS2, a novel insight into substrate-dependent optical properties.

Findings

Photoluminescence is up to ten times stronger on two-layer graphene.

Excitonic properties are effectively tuned by substrate thickness.

Layer-dependent charge transfer impacts optical responses.

Abstract

Light emission in atomically thin heterostructures is known to depend on the type of materials, number and stacking sequence of the constituent layers. Here we show that the thickness of a two-dimensional substrate can be crucial in modulating the light emission. We study the layer-dependent charge transfer in vertical heterostructures built from monolayer tungsten disulphide (WS2) on one- and two-layer epitaxial graphene, unravelling the effect that the interlayer electronic coupling has on the excitonic properties of such heterostructures. We bring evidence that the excitonic properties of WS2 can be effectively tuned by the number of supporting graphene layers. Integrating WS2 monolayers with two-layer graphene leads to a significant enhancement of the photoluminescence response, up to one order of magnitude higher compared to WS2 supported on one-layer graphene. Our findings highlight the importance of substrate engineering when constructing atomically thin layered heterostructures.