Heterostructure devices with specific and extraordinary properties can be fabricated by stacking two-dimensional crystals. Cleanliness at the inter-crystal interfaces within a heterostructure is crucial for maximizing device performance. However, because these interfaces are buried, characterizing their impact on device function is challenging. Here, we show that electron-beam induced current (EBIC) mapping can be used to image interfacial contamination and to characterize the quality of buried heterostructure interfaces with nanometer-scale spatial resolution. We applied EBIC and photocurrent imaging to map photo-sensitive graphene-MoS 2 heterostructures. The EBIC maps, together with concurrently acquired scanning transmission electron microscopy images, reveal how a device's photocurrent collection efficiency is adversely affected by nanoscale debris invisible to optical-resolution photocurrent mapping. V C 2015 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4936763] Two-dimensional (2D) crystals can be stacked to form layered heterostructures with the potential to show a tremendous variety of extraordinary properties, ranging from itinerant magnetism to superconductivity. 1 The performance of a layered heterostructure depends crucially on the layer interfaces, the quality of which is determined by the constituent materials 2,3 and any impurities introduced during fabrication. 4 Layered heterostructures are usually fabricated using some combination of the traditional wet process, 3,5,6 the "dry" method, 2,7-11 or the "dry peel" method. 3,12,13 Though efforts to improve device cleanliness are ongoing, contaminants are invariably introduced into the critical inter-layer spaces by the currently available transfer techniques. 4 Most interface-characterization techniques can either locate impurities and adsorbates or evaluate their effect on an interface's electronic properties. Global device transport measurements of, for example, resistance or charge mobility provide a crude, blind metric; they serve as an indirect gauge for interface quality but alone they give no specific information about the location and composition of impurities. In this category, capacitance spectroscopy has proved particularly powerful. 3 Coupling such transport measurements with spatially resolved characterization techniques has enabled convincing demonstrations of importance of interface cleanliness. 3,4 However, the standard mapping techniquesoptical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and cross sectional transmission electron microscopy (TEM) 3,4 -do not probe the interfacial electronic properties directly. Thus, the causal relationship between contamination or transfer residue and poor transport characteristics must be inferred from their correlated appearance.An ideal technique for characterizing the interface quality in layered heterostructures would combine local transport measurements with high-resolution, plan-view imaging of the geometry. Here, we describe scanning TEM imaging of elect...