Figure 4. In-plane heterostructure via Coulomb engineering of monolayer WS₂.

(a) First-order derivatives of the reflectance contrast of a 1L WS₂ sample for varying spatial positions across the lateral 1L WS₂/2L graphene boundary. The data are shown in the spectral range of the exciton ground state (n=1) resonance and vertically offset for clarity. (b) For the spectral range of the excited state (n=2) of the exciton with the vertical axis scaled by factor of 100 for direct comparison. Full circles in a,b indicate peak energies of the resonances, corresponding to the points of inflection of the derivatives. (c) Spatially dependent bandgap energy extracted from the exciton peak positions along the profile of the lateral WS₂/graphene heterostructure, as illustrated in the schematic representation and marked by the dashed line in the optical micrograph. The shaded areas indicate the diffraction limit corresponding to the spatial resolution of our measurement and the solid line is a guide to the eye.