Momentum Microscopy Investigation of the Local Band Structure of Monolayer WSe ₂ Flakes: Toward Optoelectronic Device in Quantum Size

Single-flake monolayer WSe₂ holds significant promise for advanced optoelectronic applications at the quantum scale, leveraging its direct band gap electronic properties that are distinct from those of the bulk material. Probing momentum-resolved electronic structure at the single-flake level remains a key challenge in two-dimensional (2D) materials research due to the spatial mismatch between micron-scale flakes and conventional photoemission techniques. Here, we use momentum microscopy (MM) to investigate the local band structure of monolayer WSe₂ flakes grown by metal-organic chemical vapor deposition (MOCVD) on bilayer graphene (BLG) using Helium-I radiation. Despite differing crystallographic orientations, all flakes exhibit identical energy-momentum (E-k) dispersions, confirming a uniform growth. However, we observe substantial variations, up to 0.16 eV, in their absolute energy alignment relative to the Fermi level, reflecting strong local electrostatic potential fluctuations. These effects are attributed to charge inhomogeneities at the WSe₂/BLG interface, likely induced by hydrogen intercalation during BLG preparation. Our results demonstrate the unique capability of MM to disentangle the intrinsic band structure from extrinsic potential variations in individual 2D flakes, which strongly influence their electronic and transport properties.