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Devices made from two-dimensional (2D) materials such as graphene ortransition metal dichalcogenides possess interesting electronic properties thatcan become accessible to experimental probes when the samples are protectedfrom deleterious environmental effects by encapsulating them between hexagonalboron nitride (hBN) layers. While the encapsulated flakes can be detectedthrough post-processing of optical images or confocal Raman mapping, thesetechniques lack the sub-micrometer scale resolution to identify tears,structural defects or impurities, which is crucial for the fabrication ofhigh-quality devices. Here we demonstrate a simple method to visualize suchburied flakes with sub-micrometer resolution, by combining Kelvin force probemicroscopy (KPFM) with electrostatic force microscopy (EFM). KPFM, whichmeasures surface potential fluctuations, is extremely effective in spottingcharged contaminants within and on top of the heterostructure, making itpossible to distinguish contaminated regions in the buried flake. When applyinga tip bias larger than the surface potential fluctuations, EFM becomesextremely efficient in highlighting encapsulated flakes and their sub-micronstructural defects. We show that these imaging modes, which are standardextensions of atomic force microscopy (AFM), are perfectly suited for locatingencapsulated conductors, for visualizing nanometer scale defects and bubbles,and for characterizing their local charge environment.

Visualizing Encapsulated Graphene, its Defects and its Charge Environment by Sub-Micrometer Resolution Electrical Imaging