UC San Diego

Two-dimensional transition metal dichalcogenides (TMDs) provide an exciting platform to study indirect excitons and excitonic devices due to their high exciton binding energy and highly tunable electronic and optical properties. This high binding energy allows for indirect excitons in TMDs to exist at temperatures well above room temperature opening the door for excitonic devices suitable for real-world application. The key to fabricating these multilayer devices is a quick and reliable method for determining the thickness or more appropriately the layer number of TMD flakes used in the fabrication process. While atomic force microscopy (AFM) is a highly accurate method of layer determination, it can only be carried out after transfer, allocating it to a verification not determination role. Previous works have utilized optical microscopy color contrast for layer determination, but this method is highly substrate dependent and has primarily been investigated on Si/SiO2, a post transfer substrate. This work establishes dark field microscopy as a suitable fabrication process-integrated method for layer determination in few-layer exfoliated MoSe2 and WSe2 by correlating dark field microscope images to AFM and photoluminescence measurements.