Graphite edge controlled registration of monolayer MoS2 crystal orientation

Abstract

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.