Graphite edge controlled registration of monolayer MoS₂ crystal orientation

Transition metal dichalcogenides such as the semiconductor MoS₂ are a class of two-dimensional crystals. The surface morphology and quality of MoS₂ grown by chemical vapor deposition are examined using atomic force and scanning tunneling microscopy techniques. By analyzing the moiré patterns from several triangular MoS₂ islands, we find that there exist at least five different superstructures and that the relative rotational angles between the MoS₂ adlayer and graphite substrate lattices are typically less than 3°. We conclude that since MoS₂ grows at graphite step-edges, it is the edge structure which controls the orientation of the islands, with those growing from zig-zag (or armchair) edges tending to orient with one lattice vector parallel (perpendicular) to the step-edge.