Orientation domain dispersions in wafer scale epitaxial monolayer WSe₂ on sapphire

Monolayer WSe₂, a 2D transition metal dichalcogenide (TMDCs), has been demonstrated as a good candidate for potential applications in optoelectronics. It is imperative to know the crystalline quality of WSe₂ over the wafer scale prior to its applications. Azimuthal reflection high-energy electron diffraction (ARHEED) is demonstrated to be a powerful technique to measure the symmetry, lattice constants, and in-plane orientation domain dispersion in wafer-scale, continuous monolayer WSe₂ epitaxially grown by metal organic chemical vapor deposition on c-plane sapphire substrate. The constructed 2D reciprocal map from ARHEED reveals few degrees’ dispersion in WSe₂ orientation domains due to the step meandering/bunching/mosaic of sapphire substrate. Minor 30° orientation domains are also observed. The methodology can be applied to study other TMDCs epitaxial monolayers, graphene, and confined atomically thin hetero-epitaxial metals.