Abstract
The properties of Van der Waals heterostructures are determined by the twist angle and the interface between adjacent layers as well as their polytype and stacking. Here we describe the use of spectroscopic Low Energy Electron Microscopy (LEEM) and micro Low Energy Electron Diffraction ({\mu}LEED) methods to measure these properties locally. We present results on a MoS$_{2}$/hBN heterostructure, but the methods are applicable to other materials. Diffraction spot analysis is used to assess the benefits of using hBN as a substrate. In addition, by making use of the broken rotational symmetry of the lattice, we determine the cleaving history of the MoS$_{2}$ flake, i.e., which layer stems from where in the bulk.
Highlights
The properties of Van der Waals (VdW) heterostructures are determined by the twist angle and the interface between adjacent layers as well as their polytype and stacking
We demonstrate that all these parameters can conveniently be obtained within one setup using low-energy electron microscopy (LEEM) and diffraction (LEED)
This is a factor of six lower than values for exfoliated MoS2 on a silicon substrate. This large linewidth, due to the roughness of SiO2, confirms the findings of Yeh et al.[21]. In contrast to their results, we find no significant broadening of the monolayer peak, indicating that the VdW force between the atomically flat hexagonal boron nitride (hBN) and MoS2 effectively prevents buckling of the latter
Summary
The VdW heterostack was fabricated through mechanical exfoliation and stamping: The MoS2 flake was exfoliated using scotch tape onto silicon oxide for thickness determination and picked up again. Spectroscopic mLEED measurements are performed by limiting the illuminated area using an aperture and taking diffraction images for a range of landing energies The shape of the diffraction spots reveals additional information, for example, the width of the central (0,0) spot (the specularly reflected electrons) is a measure for sample roughness.[15] For determination of the spotwidth, a linecut along the maximum of the central peak and perpendicular to the dispersive direction of the prisms was taken, after the data was corrected for detector effects.
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