Tailoring the dielectric screening in WS2–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 WS2 via the external dielectric screening. Embedding WS2 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 WS2-to-graphene interlayer distance and the charge carrier density in graphene. 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 nanometers 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 in screening Coulomb interactions in nearby WS2 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 × 1012 cm−2.

An open-source robust machine learning platform for real-time detection and classification of 2D material flakes

“…In our laboratory, the method has been widely adapted, with more than 10 6 images taken within 24 months by over 30 individual researchers and supporting several projects [47][48][49]. Our implementation not only speeds up sample fabrication for individuals, but has proven to have synergies in a group working on 2D materials, as exfoliated materials can be easily shared between individuals.…”

Hyperspectral photoluminescence and reflectance microscopy of 2D materials

“…We demonstrate the capability of the setup by acquiring a hyperspectral PL and RC image of a TMD monolayer sample at room temperature; further RC measurements taken with the setup can be found in the study of reference [13]. The sample is a MoSe 2 -WSe 2 in-plane heterostructure grown by chemical vapor deposition using the one-pot chemical vapor deposition growth method [25].…”

“…(gate-defined) nano-scale potentials for exciton confinement [10,11], or heterostructures of different materials or stacking orders [12,13] as well as for material-specific inhomogeneities, such as strain, charge and screening-induced disorder [14][15][16] or localized defects [17].…”

Heteroepitaxy in Organic/TMD Hybrids and Challenge to Achieve it for TMD Monolayers: The Case of Pentacene on WS2 and WSe2

“…22 For device applications, typically hBN multilayer flakes are used either as an insulating and optically transparent capping layer or as smooth support for exfoliated TMD monolayers, while hBN monolayers are mainly used as an insulation layer between 2D materials, where its roughness does not have a major influence. 23 In contrast, the optical peculiarity of TMD monolayers requires the explicit use of monolayers for the preparation of defined organic/TMD hybrid systems, e.g., to investigate optical coupling phenomena. This seems to be more challenging because 2D monolayers often exhibit the phenomenon of wrinkling, 24,25 whose influence on the subsequently grown molecular adlayers has not yet been systematically investigated.…”

“…There, it was found that thin exfoliated and transferred (multilayer) flakes often exhibit reduced surface quality and increased density of defects (e.g., steps), which affect the ordering of subsequently grown molecular films and result in coexisting defect-driven molecular film structures with different molecular orientations . For device applications, typically h BN multilayer flakes are used either as an insulating and optically transparent capping layer or as smooth support for exfoliated TMD monolayers, while h BN monolayers are mainly used as an insulation layer between 2D materials, where its roughness does not have a major influence . In contrast, the optical peculiarity of TMD monolayers requires the explicit use of monolayers for the preparation of defined organic/TMD hybrid systems, e.g., to investigate optical coupling phenomena.…”