Control of Radiative Exciton Recombination by Charge Transfer Induced Surface Dipoles in MoS2 and WS2 Monolayers.

Peng Hu,Qihua Xiong,Zheng Liu,Jun Ye,Xingzhi Wang,Xuexia He,Christian Kloc,Hui Jiang,Keke K Zhang,Kezhao Du

doi:10.1038/srep24105

Abstract

Due to the two dimensional confinement of electrons in a monolayer of 2D materials, the properties of monolayer can be controlled by electrical field formed on the monolayer surface. F4TCNQ was evaporated on MoS2 and WS2 monolayer forming dipoles between strong acceptor, F4TCNQ, and monolayers of MoS2 or WS2. The strong acceptor attracts electrons (charge transfer) and decreases the number of the ionized excitons. Free excitons undergo radiative recombination in both MoS2 and WS2. Moreover, the photoluminescence enhancement is stronger in WS2 where the exciton-phonon coupling is weaker. The theoretical model indicates that the surface dipole controls the radiative exciton recombination and enhances photoluminescence radiation. Deposition of F4TCNQ on the 2D monolayers enables a convenient control of the radiative exciton recombination and leads to the applications of these materials in lasers or LEDs.

Highlights

When an exciton, a quasiparticle consisting of an electron and a hole bound together by simple Coulomb interaction, recombines, i) photoluminescence occurs in the case of weak exciton-phonon coupling or ii) exciton recombines radiation-less increasing the phonon energy if this coupling is strong
Some reports studied PL and optical properties controlled by the charge transfer between MoS2 and metal nanoparticle[7] or graphene quantum dots[8]
It was shown that the PL intensity has been changed, and the phase transition in MoS2 monolayer is caused by charge transfer[9]

Summary

Introduction

A quasiparticle consisting of an electron and a hole bound together by simple Coulomb interaction, recombines, i) photoluminescence occurs in the case of weak exciton-phonon coupling or ii) exciton recombines radiation-less increasing the phonon energy if this coupling is strong. In a monolayer of transition metal dichalcogenides (TMD), or a two dimensional electron gas, excitons can interact with free electrons forming charged excitons known as trions, quasiparticles composed of two electrons and a hole[1]. The non-bounded excitons cannot radiative recombine producing photon (light) because they are bonded with free electrons forming trions[2,3,4,5,6]. A strong electrical field formed by gate electrode on the two-dimensional (2D) layer of TMD or dipoles on the surface of TMD monolayer can reduce the trion concentration[1]. The theoretical model indicates that the surface dipole is controlling the radiative exciton recombination, which further increases the photoluminescence

Results

Discussion

Conclusion