Activation of Raman modes in monolayer transition metal dichalcogenides through strong interaction with gold

Raman spectroscopy has become one of the most utilized methods for characterization transition metal dichalcogenides (TMDCs); however, interpretation spectra TMDC-based heterostructures been subject recent debate. Using a comprehensive combination micro-Raman and tip-enhanced spectroscopy, accompanied by ab initio simulations both frequencies intensities, we show that activation otherwise geometry-forbidden $E$ mode symmetry-forbidden ${A}_{1}$ is fingerprint strong interaction between monolayer ${MX}_{2}$ ($M$ Mo/W, $X$ S/Se) gold substrate, in contrast to weakly interacting or freestanding ${MX}_{2}$.