SERS enhancements via periodic arrays of gold nanoparticles on silver film structures.

We discuss surface enhanced Raman spectroscopy (SERS) structures aimed at providing robust and reproducible enhancements. The structures involve periodic arrays of gold nanospheres near silver film structures that may also be patterned. They enable one to excite Bloch wave surface plasmon polaritons (SPPs) that can also couple to local surface plasmons (LSPs) of the nanospheres, leading to the possibility of multiplicative enhancements. If the magnitude of the average electric field, /E/, between the particles is enhanced by g such that /E/ = g/E(0)/, /E(0)/ being the incident field, realistic finite-difference time-domain simulations show that under favorable circumstances g approximately equal 0.6 g(SPP) g(LSP), where g(SPP) and g(LSP) are enhancement factors associated with the individual components. SERS enhancements for the structures can be as high as O(g(4)) = 10(8).