Noninvasive Subsurface Electrical Probe for Encapsulated Layers in van der Waals Heterostructures

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. Determination of 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 noninvasive 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 hetero-junctions comprising graphene, hexagonal boron nitride, and transition-metal dichalcogenides. The 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 and flatness as well as local electrical properties of buried layers in a large class of nanoscale materials and vertical heterostructures.