Combined SPR and SERS: Otto and Kretschmann configurations

Combined surface enhanced Raman spectroscopy (SERS) and surface plasmon resonance (SPR) setup was proposed recently. The experimental setup requires a gold layer deposited on a glass substrate. However, due to the poor ability of sticking gold material on glass, a nanometric adhesion layer is used. In this paper we compare numerically both the SERS gain, and the SPR signal, for metallic and dielectric adhesion layers, for two substrates. We show that even if the dielectric materials can be considered as equivalent for the SPR signal, this is not the case for the SERS gain. In particular the dielectric adhesion layer reduces the sensitivity of the SERS gain to this parameter and therefore their use could be more suitable for the fabrication of the sensor. Moreover the higher the refractive index of substrate with regards to the adhesion layer is, the higher efficiency of setup is obtained, and therefore the Otto configuration seems to be more efficient than the Kretschmann one. Optimization of the thicknesses of the adhesion layer and of the gold layer can lead to a SERS gain greater than 10(3) without nanostructuring.