Combining micron-size glass spheres with silver nanoparticles to produce extraordinary field enhancements for surface-enhanced raman scattering applications

Using Mie theory and a T-matrix method, we have studied the interaction of light with a micron-size glass sphere and a dimer of silver nanoparticles in order to assess the feasibility of surface-enhanced Raman scattering (SERS) that combined dielectric hot spots with plasmon excitation. We show that when light interacts with glass spheres, there is a robust hot spot on the surface in the forward direction with dimensions of a few hundred nanometers both parallel and perpendicular to the surface. For a glass sphere in vacuum with a refractive index of 1.9 and a radius of 4 μm, we find that the electric field enhancement at this hot spot is |E|² = 500. If a dimer of silver particles (spheres of radius 30 nm placed 2 nm apart) is placed at this hot spot, the peak near-field between the nanoparticles is found to be |E| ² = 7×10⁶. This enhancement factor, which is approximately the product of the dimer-only enhancement factor (~10⁴) and the hot spot enhancement, is comparable to the largest field enhancements that we have obtained with other nanoparticle structures. It is large enough that the observation of single molecule SERS might be possible with this structure.