  We report the implementation of energy dispersive X-ray spectroscopy for
layered semiconductors in the form of atomically thin transition metal
dichalcogenides. The technique is based on a scanning electron microscope
equipped with a silicon drift detector for energy dispersive X-ray analysis. By
optimizing operational parameters in numerical simulations and experiments, we
achieve layer-resolving sensitivity for few-layer crystals down to the
monolayer limit and demonstrate elemental composition profiling in vertical and
lateral heterobilayers of transition metal dichalcogenides. The technique can
be straight-forwardly applied to other layered two-dimensional materials and
van der Waals heterostructures, thus expanding the experimental toolbox for
quantitative characterization of layer number, atomic composition, or alloy
gradients for atomically thin materials and devices.
