  Raman scattering is a ubiquitous phenomenon in light-matter interactions
which reveals a material's electronic, structural and thermal properties.
Controlling this process would enable new ways of studying and manipulating
fundamental material properties. Here, we report a novel Raman scattering
process at the interface between different van der Waals (vdW) materials as
well as between a monolayer semiconductor and 3D crystalline substrates. We
find that interfacing a WSe2 monolayer with materials such as SiO2, sapphire,
and hexagonal boron nitride (hBN) enables Raman transitions with phonons which
are either traditionally inactive or weak. This Raman scattering can be
amplified by nearly two orders of magnitude when a foreign phonon mode is
resonantly coupled to the A exciton in WSe2 directly, or via an A'1 optical
phonon from WSe2. We further showed that the interfacial Raman scattering is
distinct between hBN-encapsulated and hBN-sandwiched WSe2 sample geometries.
This cross-platform electron-phonon coupling, as well as the sensitivity of 2D
excitons to their phononic environments, will prove important in the
understanding and engineering of optoelectronic devices based on vdW
heterostructures.
