Interlayer couplings, Moiré patterns, and 2D electronic superlattices in MoS/WSe hetero-bilayers.

By using direct growth, we create a rotationally aligned MoS/WSe hetero-bilayer as a designer van der Waals heterostructure. With rotational alignment, the lattice mismatch leads to a periodic variation of atomic registry between individual van der Waals layers, exhibiting a Moiré pattern with a well-defined periodicity. By combining scanning tunneling microscopy/spectroscopy, transmission electron microscopy, and first-principles calculations, we investigate interlayer coupling as a function of atomic registry. We quantitatively determine the influence of interlayer coupling on the electronic structure of the hetero-bilayer at different critical points. We show that the direct gap semiconductor concept is retained in the bilayer although the valence and conduction band edges are located at different layers. We further show that the local bandgap is periodically modulated in the - direction with an amplitude of ~0.15 eV, leading to the formation of a two-dimensional electronic superlattice.