Oxygen passivation mediated tunability of trion and excitons in MoS$_2$

TL;DR

This study investigates how oxygen exposure affects the excitonic properties of MoS₂ by combining in situ spectroscopic ellipsometry and ab initio calculations, revealing tunable exciton behavior linked to sulfur vacancy passivation.

Contribution

It demonstrates the environmental tunability of excitonic effects in MoS₂ through oxygen passivation, combining experimental and theoretical insights.

Findings

Spectral weights of excitons decrease after annealing

Spectral weights recover upon oxygen exposure

Oxygen passivation influences MoS₂ optical properties

Abstract

Using wide spectral range in situ spectroscopic ellipsometry with systematic ultra high vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS$_2$ isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A ($1.92$ eV) and B ($2.02$ eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the bandstructure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This work unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS$_2$.