Plasmonic "Nanowave" Substrates for SERS: Fabrication and Numerical Analysis.

The "Nanowave" substrate, comprising a close-packed array of nanospheres onto which a thin metal shell of silver or gold is deposited, was first fabricated in our laboratory in 1984 and used as a surface-enhanced Raman scattering (SERS)-active substrate for the sensitive and reproducible detection of analytes. More than twenty-five years after the first experimental demonstration of the effectiveness of this substrate, numerical simulations are sufficiently powerful and versatile to mimic this geometry in three dimensional space and confirm the experimentally measured plasmonic behavior at the substrate's surface. The study confirms that an in-plane polarized incident plane wave generates strong enhancements in the interstitial spaces between individual metal-coated nanospheres, thus producing closely packed arrays of hot spots underlining the strong SERS effect of the Nanowave substrate structures. The surface-averaged SERS enhancement exhibited by the Nanowaves was evaluated and compared for different metal thicknesses. The effect of structural confinement on the plasmonic behavior of the Nanowave structure was investigated by varying the structural confinement of the substrate in the plane parallel to the incident excitation. The Nanowave is an inexpensive, reproducible and effective plasmonics-active substrate that has the potential to be used for SERS studies requiring high detection sensitivity.