Structural Effects in the Electromagnetic Enhancement Mechanism of Surface-Enhanced Raman Scattering: Dipole Reradiation and Rectangular Symmetry Effects for Nanoparticle Arrays

Surface-enhanced Raman scattering (SERS) enhancement factors for Ag and Au sphere array structures are determined by rigorously including dipole reradiation in a T-matrix formalism. Comparisons are made with the more commonly used local field, enhancement due to plane-wave excitation, vertical bar E(r(0);omega)vertical bar(2)vertical bar E(r(0);omega(s))vertical bar(2) which for zero Stokes shift is vertical bar E(r(0);omega)vertical bar(4) to determine the errors associated with this approximation. Substantial errors (factors of 10-100) are found for the peak enhancements at a scattering angle well away from the incident direction, but for backscattering, the errors are negligible. We also present vertical bar E vertical bar(4) enhancement factors using a periodic boundary discrete dipole approximation method for several metal strip array structures, and we show that a certain combination of rectangular array structure and strip properties leads to electromagnetic enhancement factors for mixed photonic-plasmonic resonances that are considerably higher than can be produced with either square arrays or 1-D arrays based on the same particles and spacings.