Twisted MoSe₂/WSe₂ Heterostructure: Spatially-Resolved Moiré Superlattice Analysis via Advanced Transmission Electron Microscopy

Van der Waals heterostructures, when twisted, present unique opportunities for nanoscale electronic property modulation. One notable manifestation is the Moiré pattern, resulting from lattice mismatch or rotational misalignment. This pattern can adjust the electronic band structure, leading to phenomena like Moiré excitons, attributed to rapid interlayer charge transfers in Transition Metal Dichalcogenide, and band gap modulation. Analysing these nanoscale events demands techniques blending spatial and energy resolution. In this work, we probe MoSe₂/WSe₂ heterostructures using cutting-edge Transmission Electron Microscopy techniques to achieve atomic-level structural insights resolution into the Moiré superlattice. Electron Energy Loss Spectroscopy is employed to chart the electronic characteristics. employing our inhouse developed open-source tool, EELSFitter, we quantitatively delineate the band gap’s local variations within the Moiré superlattice, and map Moire-induced exciton shifts. We observe that the value of the band gap follows the Moiré periodicity varying between 1.22 eV at the edges of the Moiré unit cells, where there is a lattice mismatch between the MoSe₂ and WSe₂, to 1.36 eV within the Moiré unit cells.