Small-angle lattice rotations in graphene on Ru(0001)

Lattice rotations in graphene on Ru(0001) are investigated with low-energy electron microscopy and micro-low-energy electron diffraction. The measurements place an upper limit, 250 nm, on the racemic length scale of the recently reported chirality in this system, arising from rotated features within the unit cell. On a longer length scale, small rotations from orientational coincidence with the substrate lattice are found to be present in the vast majority of the graphene layer. The resulting proliferation of small-angle grain boundaries may influence the properties of the graphene layer that is otherwise free of large-angle rotational variants and oriented uniformly with the substrate.