Cascade Electric Field Enhancement in the Orthogonal-Nanorod Structures

The transverse mode electron oscillations contribute to most of the surface-enhanced Raman scattering (SERS) intensity from the nanorod array substrates. To enhance the transverse mode electron oscillation and improve the SERS enhancements, the local electric field distribution of the orthogonal-nanorod structures, composed of two parallel horizontal nanorods in between two parallel vertical nanorods, has been studied. The local electric fields of the longitudinal mode along the horizontal nanorods act as the excitation for the transverse mode electron oscillations in vertical nanorods, leading to the cascade enhancements of the electric fields around the vertical nanorods. In addition, the plasmon peaks of the longitudinal modes can be tuned by changing the lengths and the widths of the horizontal nanorods and the separations between horizontal and vertical nanorods. These results would be much helpful to engineer SERS substrates to obtain larger SERS enhancements.