Mapping Graphene Grain Orientation by the Growth of WS2 Films with Oriented Cracks

We map the lattice orientation of graphene grains (domains) larger than a centimeter by measuring the orientation of cracks in a WS2 film grown on graphene that had been previously grown by chemical vapor deposition (CVD) on Cu foils. A WO3 film was first deposited on the graphene film and then converted to a WS2 film by CVD sulfurization. The WS2 film was found to contain cracks that, as found by electron diffraction and optical birefringence, are always aligned along the armchair direction of the graphene lattice. We find that this method is significantly advanced compared to any published methods for the analysis of the grain structure, as it provides simultaneous and high-contrast mapping of grain orientation without needing further analysis.