Tailoring the dielectric screening in WS${}_2$-graphene heterostructures

Abstract

The environment contributes to the screening of Coulomb interactions in two-dimensional semiconductors. This can potentially be exploited to tailor material properties as well as for sensing applications. Here, we investigate the tuning of the band gap and the exciton binding energy in the two-dimensional semiconductor WS${}_2$ via the external dielectric screening. Embedding WS${}_2$ in van der Waals heterostructures with graphene and hBN spacers of thicknesses between one and 16 atomic layers, we experimentally determine both energies as a function of the \WS-to-graphene interlayer distance. We find that the modification to the band gap as well as the exciton binding energy are well described by a one-over-distance dependence, with a significant effect remaining at several nm distance, at which the two layers are electrically well isolated. This observation is explained by a screening arising from an image charge induced by the graphene layer. Furthermore, we find that the effectiveness of graphene to screen Coulomb interactions in nearby WS${}_2$ depends on its doping level and can therefore be controlled via the electric field effect. We determine that, at room temperature, it is modified by approximately 20\% for charge carrier densities of $2\times 10^{12}$ cm${}^{-2}$.

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• Nano-optics of transition metal dichalcogenides and their van der Waals heterostructures with electron spectroscopies
• Benchmarking the integration of hexagonal boron nitride crystals and thin films into graphene-based van der Waals heterostructures
• Hyperspectral photoluminescence and reflectance microscopy of 2D materials
• MaskTerial: A Foundation Model for Automated 2D Material Flake Detection
• Excitons in epitaxially grown WS2 on Graphene: a nanometer-resolved EELS and DFT study
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• Photoluminescence Detection of Polytype Polarization in r-MoS2 Enabled by Asymmetric Dielectric Environments
• Designable exciton mixing through layer alignment in WS${}_2$-graphene heterostructures
• Subnanometric control of coupling between WS${}_2$ monolayers with a molecular spacer