Orientation dependent interlayer stacking structure in bilayer MoS₂ domains

We have studied the atomic structure of small secondary domains that nucleate on monolayer MoS₂ grown by chemical vapour deposition (CVD), which form the basis of bilayer MoS₂. The small secondary bilayer domains have a faceted geometry with three-fold symmetry and adopt two distinct orientations with 60° rotation relative to an underlying monolayer MoS₂ single crystal sheet. The two distinct orientations are associated with the 2H and 3R stacking configuration for bilayer MoS₂. Atomic resolution images have been recorded using annular dark field scanning transmission electron microscopy (ADF-STEM) that show the edge termination, lattice orientation and stacking sequence of the bilayer domains relative to the underlying monolayer MoS₂. These results provide important insights that bilayer MoS₂ growth from 60° rotated small nuclei on the surface of monolayer MoS₂ could lead to defective boundaries when merged to form larger continuous bilayer regions and that pure AA' or AB bilayer stacking may be challenging unless from a single seed.