Atomic Reconstruction of Large-Lattice-Mismatched Transition Metal Dichalcogenides Heterobilayers into Strained-Commensurate Structures

Moiré superlattices between vertically stacked van der Waals (vdW) layers with twist angle or lattice mismatch generate periodic moiré potentials, which induce renormalization of electronic band structures and corresponding modulation of electrical and optical properties of moiré crystals. In addition, lots of attentions have been paid for spontaneous atomic reconstruction of small-mismatched vdW layers into periodic commensurate domains separated by incommensurate boundaries because of unprecedented physical properties of these unique vdW layers. Unlike small-mismatched vdW layers, the spontaneous reconstruction has not been observed in large-mismatched vdW layers owing to their large formation energy of commensurate structures. Here, we report thermally induced atomic reconstruction of a large-mismatched MoS₂/MoSe₂ heterobilayer (lattice mismatch = 3.88%) into a strained-commensurate (SC) heterostructure that has angle- and lattice-matched commensurate domains separated by saddle point (SP) structures through hBN-encapsulation annealing. We verified that the SP structure has large dilatational and shear strains of 4% and the SC structure exhibited splitting of the intralayer excitons owing to the inhomogeneous strain distribution. Our work verifies that even hetero-bilayers with large lattice mismatches can transform into lattice-aligned heterostructures regardless of twist angle and expands our understanding for electrical and optical properties of vdW heterostructures with new stacking sequences.