A molecular optomechanics approach to Surface-Enhanced Raman Scattering - Javier Aizpurua

Surface-Enhanced Raman Scattering (SERS) exploits the strong interaction between molecules and plasmonic resonances in metallic nanostructures enabling the characterization of vibrational modes of a very small amount of molecules. A classical description of SERS in plasmonic nanoantennas properly addresses the strong enhancement of the Raman lines in the emission spectrum, with the properties of molecular vibrations assumed to be fixed. A recently introduced quantum description of SERS, based on molecular optomechanics [1,2,3] shows how the width and frequency of the Raman lines can change for very intense laser powers, corresponding to a significant modification of the effective losses and energy of the molecular vibrations, respectively. These changes come together with a strong non-linear dependence of the emitted Raman signal on the intensity of the incident laser [4-6].
In this talk, a description of the molecular optomechanics approach to SERS will be given, together with an analysis of specific aspects relevant to molecular vibrations and to plasmonic modes in this context. The molecular optomechanics approach often considers a single plasmonic cavity mode, and we revise the importance of considering the full plasmonic response in the interaction [7,8]. We further consider a situation where multiple molecules are placed in the plasmonic nanocavity, giving rise to the formation of collective vibrational modes [9]. We show all these results in the context of recent experimental observations in SERS[10].
[1] Roelli, P., Galland, S. et al., 2016. Nat. Nanotech. 11, 164.[2] Schmidt, M. K., Esteban, R. et al., 2016, ACS Nano 10, 6291.[3] Esteban, R., Baumberg, J.J., Aizpurua,J., 2022. Acc. Chem. Res. 6291 [4] Schmidt, M. K. , Esteban, R. et al., 2017, Faraday Discuss. 205, 31.[5] Le Ru, E. C. and Etchegoin. 2006, P. G. Faraday Discuss. 132, 63.[6] Benz, F., et al., 2016, Science. 354, 6313.[7] Dezfouli M. K. and Hughes, S., 2017, ACS Photonics, 4, 1245.[8] Zhang, Y., Esteban. R. et al., 2021, Nanoscale 13, 1938.[9] Zhang, Y., Aizpurua. J. and Esteban, R., 2020, ACS Photonics 7, 1676.[10] Deacon, W. M., Zhang, Y. et al., submitted.