Imaging lattice reconstruction in homobilayers and heterobilayers of transition metal dichalcogenides

Moiré interference effects have profound impact on the optoelectronic properties of vertical van der Waals structures. Here we establish secondary electron imaging in a scanning electron microscope as a powerful technique for visualizing registry-specific domains in vertical bilayers of transition metal dichalcogenides with common moiré phenomena. With optimal parameters for contrast-maximizing imaging of high-symmetry registries, we identify distinct crystal realizations of WSe${}_2$ homobilayers and MoSe${}_2$-WSe${}_2$ heterobilayers synthesized by chemical vapor deposition, and demonstrate ubiquitous lattice reconstruction in stacking-assembled bilayers with near parallel and antiparallel alignment. Our results have immediate implications for the optical properties of registry-specific excitons in layered stacks of transition metal dichalcogenides, and demonstrate the general potential of secondary electron imaging for van der Waals twistronics.