Blue shifting of the A exciton peak in folded monolayer 1H-MoS2

TL;DR

This paper demonstrates that folding monolayer 1H-MoS2 causes a blue shift in the A exciton peak due to exciton screening effects, contrasting with typical band structure expectations.

Contribution

It provides experimental evidence of blue shifting in folded MoS2 and offers a theoretical explanation based on exciton screening effects.

Findings

Folding MoS2 enhances photoluminescence quantum yield.

Folding causes a 90 meV blue shift in the A exciton peak.

Theoretical analysis attributes the shift to exciton screening.

Abstract

The large family of layered transition-metal dichalcogenides is widely believed to constitute a second family of two-dimensional (2D) semiconducting materials that can be used to create novel devices that complement those based on graphene. In many cases these materials have shown a transition from an indirect bandgap in the bulk to a direct bandgap in monolayer systems. In this work we experimentally show that folding a 1H molybdenum disulphide (MoS2) layer results in a turbostratic stack with enhanced photoluminescence quantum yield and a significant shift to the blue by 90 meV. This is in contrast to the expected 2H-MoS2 band structure characteristics, which include an indirect gap and quenched photoluminescence. We present a theoretical explanation to the origin of this behavior in terms of exciton screening.