Imaging lattice reconstruction in homobilayers and heterobilayers of transition metal dichalcogenides

Abstract

Moiré interference effects influence profoundly the optoelectronic properties of vertical van der Waals structures. Here we systematically establish secondary electron imaging in a scanning electron microscope as a powerful technique for visualizing reconstruction of moiré lattices into registry-contrasting domains in vertical homobilayers and heteorbilayers of transition metal dichalcogenides (TMDs) with parallel and antiparallel alignment. With optimal parameters for contrast-maximizing imaging of high-symmetry registries, we identify distinct crystal realizations of WSe2 homobilayers and MoSe2-WSe2 heterostructures synthesized by chemical vapor deposition. In particular, we find evidence for a mutually exclusive competition between R h X and R h M registries, manifesting in complete reconstruction of bilayer crystals into one distinct registry or alternating large-area domains in R h X and R h M stacking. Our results have immediate implications for the optical properties of registry-specific excitons in layered stacks of TMDs, and demonstrate the general potential of secondary electron imaging for van der Waals twistronics.