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In this work, we perform aberration-corrected energy-filtered TEM (EFTEM) and low-loss electron energy-loss spectroscopy (EELS) with two-dimensional (2D) materials. In particular, the carbon K-edge EFTEM signal is analyzed for a monolayer of graphene, and the low-loss EELS spectra of graphene and molybdenum disulfide (MoS���) heterostructures are investigated by the technique of momentum-resolved EELS. With EFTEM in the Cc/Cs-corrected ���SALVE III��� low-voltage transmission electron microscope, we demonstrate lattice contrast in zero-loss, plasmon-loss, and C-K-edge images. Both bright-atom contrast and dark-atom contrast are observed in all three cases, and focus series show that even for the C-K edge, contrast inversions can be caused by a change in the defocus. For an analysis of the image contrast in direct space, all raw EFTEM data are averaged over a large number of unit cells to improve the signal-to-noise-ratio. In the low-loss regime of EELS (0���50 eV), our momentum-resolved experimental data for 2D heterostructures of graphene and MoS��� can be understood by a combination of ab initio simulations and dielectric model calculations. Therefore, the low-loss EELS signals of 2D multilayers and heterostructures are described on the basis of time-dependent density functional theory calculations for the constituent monolayers. Expanding on a layered-electron gas model for graphene, multilayers and heterostructures with MoS��� are eventually modeled by microscopic dielectric calculations that are in good agreement with our experimental EELS data. The necessity of models beyond the layered electron-gas model is demonstrated by calculations for multilayer and bulk MoS���.

High-energy electronic excitations of graphene and MoS2 heterostructures are investigated by momentum-resolved electron energy-loss spectroscopy in the range of 1 to 35 eV. The interplay of excitations on different sheets is understood in terms of long-range Coulomb interactions and is simulated using a combination of ab initio and dielectric model calculations. In particular, the layered electron-gas model is extended to thick layers by including the spatial dependence of the dielectric response in the direction perpendicular to the sheets. We apply this model to the case of graphene/MoS2/graphene heterostructures and discuss the possibility of extracting the dielectric properties of an encapsulated monolayer from measurements of the entire stack., acceptedVersion

International audience; High-energy electronic excitations of graphene and MoS2 heterostructures are investigated by momentum-resolved electron energy-loss spectroscopy in the range of 1 to 35 eV. The interplay of excitations on different sheets is understood in terms of long-range Coulomb interactions and is simulated using a combination of ab initio and dielectric model calculations. In particular, the layered electron-gas model is extended to thick layers by including the spatial dependence of the dielectric response in the direction perpendicular to the sheets. We apply this model to the case of graphene/MoS2/graphene heterostructures and discuss the possibility of extracting the dielectric properties of an encapsulated monolayer from measurements of the entire stack.