Apex-Enhanced Raman Spectroscopy Using Double-Hole Arrays in a Gold Film

Periodic arrays of subwavelength double-hole apertures in a 100 nm gold film were used for surface-enhanced Raman scattering (SERS). The periodicity of the arrays and the double-hole overlap were varied to measure their effect on the Raman enhancement. The experiments were realized in two geometries:  forward-scattering (transmission through the holes) and back-scattering. Significant enhancement in the SERS signal was observed in both geometries for the optimized substrates. Electromagnetic calculations verified that the local electromagnetic field intensity was indeed maximized for the arrays that produced the largest SERS effect. The double-hole structure was shown to produce controlled and predictable SERS due to the enhanced field localized at the apexes formed by the overlap between the holes.