Using wide spectral range in situ spectroscopic ellipsometry with systematic ultrahigh vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS2 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 band structure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This Letter unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS2.
|Original language||English (US)|
|Journal||Physical Review Letters|
|State||Published - Aug 16 2017|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work is supported by ASTAR Pharos Grant No. R-144-000-359-305 and SERC 1527000012, Singapore National Research Foundation under its Competitive Research Funding (NRF-CRP 8-2011-06 and No. R-398-000-087-281), MOE-AcRF Tier-2 (MOE2010-T2-2-121), and FRC (R-144-000-368-112), and the Medium Sized Centre Programme and CRP Grant "Novel 2D materials with tailored properties: Beyond graphene" (R-144-000-295-281). The first-principles calculations were carried out on the Centre for Advanced 2D Materials and Graphene Research Centre high-performance computing facilities.