Coupled 2D Semiconductor–Molecular Excitons with Enhanced Raman Scattering

Two-dimensional (2D) material–organic interfaces offer a platform to realize hybrid materials with tunable optical properties that are determined by the interactions between the disparate materials. This is particularly attractive for tailoring the optoelectronic properties of semiconducting monolayer transition metal dichalcogenides (TMDs). Here, we demonstrate evidence of coupled 2D semiconductor–molecular excitons with enhanced optical properties, which results from the atomically thin heterojunction. Specifically, we investigate the hybridization of the 2.16 eV WSe2 B exciton with the 2.20 eV transition of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), observed by enhanced resonant Raman scattering by the PTCDA vibrational modes, with enhancements by a factor of nearly 20. The effect can be understood from a coupled oscillator model in which the strong absorption resonance of the WSe2 monolayer increases the Raman scattering efficiency of the PTCDA. The Raman enhancement diminishes with increasing WSe2 thickness, which is attributed to a reflectivity effect that reduces the intensity at the surface. The proposed hybridization effect may lead to new investigations into the nature of coupled excitons in atomically thin junctions.