  Van der Waals heterostructures formed by stacking different atomically thin
layered materials have emerged as the sought-after device platform for
electronic and optoelectronic applications. Determining the spatial extent of
all the encapsulated components in such vertical stacks is key to optimal
fabrication methods and improved device performance. Here we employ
electrostatic force microscopy as a fast and non-invasive microscopic probe
that provides compelling images of two dimensional layers buried over 30 nm
below the sample surface. We demonstrate the versatility of the technique by
studying heterojunctions comprising graphene, hexagonal boron nitride and
transition metal dichalcogenides. Work function of each constituent layer acts
as a unique fingerprint during imaging, thereby providing important insights
into the charge environment, disorder, structural imperfections and doping
profile. The technique holds great potential for gaining a comprehensive
understanding of the quality, flatness as well as local electrical properties
of buried layers in a large class of nanoscale materials and vertical
heterostructures.
