Simulation of surface enhanced vibrational spectroscopy

T. Colleu-Banse1, A. Fekete1, L. Henrard1

1 Department of Physics and NISM Institute, University of Namur

Surface Enhance Infrared Absorption (SEIRA) is an experimental method where trace amounts of a compound are detected by enhancing their absorption in the infrared spectrum1. This enhancement is a result of the interaction of the molecules with a localized plasmon, usually from a metallic nano-particle. A common hypothesis is that the molecule is mainly affected by the high local electric-field resulting from the plasmonic resonance, with some sources suggesting that the enhancement is proportional to the square of the electric-field intensity2,3. However, the exact nature of this interaction Has not been analysed into details.

Here we simulate this electromagnetic interaction within a Discrete Dipole Approximation. Those simulations yield similar behaviour to what can be found in experimental studies with a decrease of the overall cross-section absorption at the molecule resonance when it coincides with the plasmonic resonance. This decrease is tied to the effect of the molecule on the polarization of the nano-particle according to our results. This is unexpected as the molecular polarizability is very small compared to the plasmonic response of the metallic nano-particle. This work sheds a brighter light on the mechanism of SEIRA.

  1. Dong, L., Yang, X., Zhang, C., Cerjan, B., Zhou, L., Tseng, M.L., Zhang, Y., Alabastri, A., Nordlander, P., Halas, N.J., Nano Lett. 2017, 17, 5768–5774.
  2. Neubrech, F., Beck, S., Glaser, T., Hentschel, M., Giessen, H., Pucci, A., ACS Nano. 2014, 8, 6250–6258.
  3. Neuman, T., Huck, C., Vogt, J., Neubrech, F., Hillenbrand, R., Aizpurua, J., Pucci, A., J. Phys. Chem. C 2015, 119, 26652–26662.