Coupled subwavelength gratings for surface-enhanced Raman spectroscopy.

Dual subwavelength Ag gratings with a small gap of about 15 nm are demonstrated to provide a huge additional SERS enhancement, more than 10(3) fold in scattering efficiency over normal SERS on an Ag film due to the strong plasmon coupling, which is simulated by theoretical calculation. The simulation also shows the advantages of the coupled two-layer gratings over the one-layer grating for SERS measurement. Our study provides a promising and feasible way of structure design for extremely sensitive substrates of SERS.