The interplay between excitons and phonons governs the optical and electronic properties of transition metal dichalcogenides (TMDs). Even though a number of linear and nonlinear optical-, electron-, and photoelectron-based approaches have been developed and/or adopted to characterize excitons and phonons in single/few-layer TMDs and their heterostructures, no existing method is capable of directly probing ultralow-frequency and interlayer phonons on the nanoscale. To this end, we developed ultralow-frequency tip-enhanced Raman spectroscopy, which allows spectrally and spatially resolved chemical and structural nanoimaging of WSe2/WS2 heterostructures. In this work, we apply this method to analyze phonons in nanobubbles that are sustained in these heterobilayers. Our method is capable of directly probing interlayer (de)coupling using our novel structurally sensitive nano-optical probe and the interplay between excitons and interlayer/intralayer phonons through correlation analysis of the recorded spectral images.

Horiba Instruments Inc 359 Bel Marin Keys Boulevard Suite 18 Novato California 94949 United States

J Heyrovský Institute of Physical Chemistry Czech Academy of Sciences Dolejškova 2155 3 182 23 Prague Czech Republic

Physical Sciences Division Pacific Northwest National Laboratory P O Box 999 Richland Washington 99352 United States

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Roadmap for Photonics with 2D Materials