van der Waals heterostructures (vdW-HSs) integrate dissimilar
materials
to form complex devices. These rely on the manipulation of charges
at multiple interfaces. However, at present, submicrometer variations
in strain, doping, or electrical breakages may exist undetected within
a device, adversely affecting macroscale performance. Here, we use
conductive mode and cathodoluminescence scanning electron microscopy
(CM-SEM and SEM-CL) to investigate these phenomena. As a model system,
we use a monolayer WSe2(1L-WSe2) encapsulated
in hexagonal boron nitride (hBN). CM-SEM allows for quantification
of the flow of electrons during the SEM measurements. During electron
irradiation at 5 keV, up to 70% of beam electrons are deposited into
the vdW-HS and can subsequently migrate to the 1L-WSe2.
This accumulation of charge leads to dynamic doping of 1L-WSe2, reducing its CL efficiency by up to 30% over 30 s. By providing
a path for excess electrons to leave the sample, near full restoration
of the initial CL signal can be achieved. These results indicate that
the trapping of charges in vdW-HSs during electron irradiation must
be considered, in order to obtain and maintain optimal performance
of vdW-HS devices during processes such as e-beam lithography or SEM.
Thus, CM-SEM and SEM-CL form a toolkit through which nanoscale characterization
of vdW-HS devices can be performed, allowing electrical and optical
properties to be correlated.