Raman scattering enhancement by dielectric spheres

Raman scattering experiments were performed on Si(60nm)/metal/substrate structures with and without silica microspheres (with a diameter between 0.5 and 5 mu m) on top. Raman scattering from the thin Si layer exhibits enhancements (similar to 20) due to the dielectric spheres, where the enhancement factors depend on the diameter of the spheres. The interaction between light and dielectric spheres has been simulated by finite difference time domain calculations (FDTD), wherein particularly the electric energy density (ED) distribution in the thin Si layer was of concern. For microspheres with a diameter less than similar to 3 mu m, the transverse ED distribution (perpendicular to the incident light direction) within the Si layer is characterised by a single peak centered on the optical axis. For larger diameters, a multimodal transverse ED distribution develops where the maximum is not centered on the optical axis. Using an ad-hoc approach for surface enhanced Raman scattering in combination with the FDTD calculations, the experimental Raman observations are well accounted for. Copyright (c) 2013 John Wiley & Sons, Ltd.