Nonradiative energy transfer enhances Raman intensity in layered heterostructure

Since the discovery of Graphene enhanced Raman scattering, layered materials and their heterostructures are emerging as promising candidates for realizing Raman enhancement on flat surfaces. While most of the Raman enhancement studies on these materials are based on charge transfer interaction, here, we experimentally demonstrate for the first time, a strong enhancement of Raman intensity through nonradiative energy transfer (NRET) in a layered heterostructure. We achieve a ten-fold Raman enhancement of a monolayer transition metal dichalcogenide (1L-TMD, such as 1L-MoS₂ and 1L-WS₂) stacked on a multilayer SnSe₂. Spectral resonance, extreme spatial proximity and in-plane orientation of dipoles result in strong dipole-dipole coupling that enables NRET driven Raman enhancement even when a barrier layer like hBN is introduced between 1L-TMD and SnSe₂. We corroborate the evidence for NRET driven Raman enhancement by decoupling it from other effects and demonstrating its tunability through modulation of spectral overlap between 1L-TMD and SnSe₂ by varying the sample temperature. Observation of such non-local, uniform Raman enhancement over a wide junction area opens new ways to engineer sensing mechanisms using NRET in tandem with other existing enhancement techniques.