One-dimensional Moiré Landscape in Transition Metal Dichalcogenide Heterostructures Uncovered with Electron Spectromicroscopy

Unique properties can be tailored from the moiré periodicity of TMD heterobilayers, however, only minor focus has been put on deviations from the two-dimensional periodic moiré potentials. An ideal technique to correlate directly structural variations to local excitonic behavior is aberration-corrected scanning transmission electron microscopy (AC-STEM) capable of resolving the sub-nanometer scale periodicities combined with multimodal signals. Here, cryogenic monochromated (5–10 meV) electron energy-loss spectroscopy (EELS) and four-dimensional (4D)-STEM in an AC-STEM are used to investigate the excitonic response and strain relaxation at one-directional structural discontinuities in rotationally aligned MoSe₂/WSe₂ heterobilayers with h-BN encapsulation. The ~0.2% heterobilayer lattice mismatch is accommodated at localized domain boundaries of various densities (singles, pairs, arrays of multiple) that separate domains of commensurate H-stacking of 10¹–10² nm in size. The nature of the boundaries and how they modify the local excitonic response of the lowest energy intralayer excitons will be discussed.