Atomically thin dichalcogenide heterostructures and interfaces measured via cathodoluminescence in scanning transmission electron microscope

Atomically thin transition metal dichalcogenides (TMDs) and associated heterostructures have distinct opto-electronic properties including enhanced luminescence and high on-off current ratios. However, optoelectronic properties measured using conventional methods are limited to micro-milimeter scale and with no direct structural correlation, despite the fact that relevant property fluctuations can be caused by significantly smaller structural features. We use cathodoluminescence (CL) in a scanning transmission electron microscope (STEM) as a nanoscale probe that offers direct structure-optical correlation with high spatial resolution.
We present the first, to our knowledge, STEM-CL measurements of monolayer tungsten disulfide (WS₂) encapsulated between hexagonal boron nitride (HBN). We measure spatially inhomogeneous luminescence resulting from variations in the interface quality between layers, and provide a direct way to probe optical properties of TMD heterostructures on the nanoscale. We also discuss role of the electron beam and the ways to minimize it to measure intrinsic properties of TMDs. STEM-CL offers to be a powerful method to directly measure structure-optical correspondence, with applications in measuring lateral or vertical TMD heterostructures and alloys.