Nanoscale Cathodoluminescence and Conductive Mode Scanning Electron Microscopy of van der Waals Heterostructures

van der Waals heterostructures (vdW-HSs) integrate dissimilarmaterialsto form complex devices. These rely on the manipulation of chargesat multiple interfaces. However, at present, submicrometer variationsin strain, doping, or electrical breakages may exist undetected withina device, adversely affecting macroscale performance. Here, we useconductive 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) encapsulatedin hexagonal boron nitride (hBN). CM-SEM allows for quantificationof the flow of electrons during the SEM measurements. During electronirradiation at 5 keV, up to 70% of beam electrons are deposited intothe 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 providinga path for excess electrons to leave the sample, near full restorationof the initial CL signal can be achieved. These results indicate thatthe trapping of charges in vdW-HSs during electron irradiation mustbe considered, in order to obtain and maintain optimal performanceof vdW-HS devices during processes such as e-beam lithography or SEM.Thus, CM-SEM and SEM-CL form a toolkit through which nanoscale characterizationof vdW-HS devices can be performed, allowing electrical and opticalproperties to be correlated.