  The electronic properties of two-dimensional materials such as graphene are
extremely sensitive to their environment, especially the underlying substrate.
Planar van der Waals bonded substrates such as hexagonal boron nitride (hBN)
have been shown to greatly improve the electrical performance of graphene
devices by reducing topographic variations and charge fluctuations compared to
amorphous insulating substrates}. Semiconducting transition metal
dichalchogenides (TMDs) are another family of van der Waals bonded materials
that have recently received interest as alternative substrates to hBN for
graphene as well as for components in novel graphene-based device
heterostructures. Additionally, their semiconducting nature permits dynamic
gate voltage control over the interaction strength with graphene. Through local
scanning probe measurements we find that crystalline defects intrinsic to TMDs
induce scattering in graphene which results in significant degradation of the
heterostructure quality, particularly compared to similar graphene on hBN
devices.
