Crossover between rigid and reconstructed moiré lattice in <i>h</i>-BN-encapsulated twisted bilayer WSe₂ with different twist angles

A moiré lattice in a twisted-bilayer transition metal dichalcogenide (tBL-TMD) exhibits a complex atomic reconstruction effect when its twist angle is less than a few degrees. The influence of the atomic reconstruction on material properties of the tBL-TMD has been of particular interest. In this study, we performed scanning transmission electron microscopy (STEM) imaging of a moiré lattice in <i>h</i>-BN-encapsulated twisted bilayer WSe₂ with various twist angles. Atomic-resolution imaging of the moiré lattice revealed a reconstructed moiré lattice below a crossover twist angle of ∼4° and a rigid moiré lattice above this angle. Our findings indicate that <i>h</i>-BN encapsulation has a considerable influence on lattice reconstruction, as the crossover twist angle was larger in <i>h</i>-BN-encapsulated devices compared to non-encapsulated devices. We believe that this difference is due to the improved flatness and uniformity of the twisted bilayers with <i>h</i>-BN encapsulation. Our results provide a foundation for a deeper understanding of the lattice reconstruction in twisted TMD materials with <i>h</i>-BN encapsulation.