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.
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