Scalable, cost-effective plasmonic-interference coupling design

Typical excitations in metal nanostructures are localized surface plasmon resonances (LSPR) and propagating surface plasmon polaritons (SPPs) at metal-dielectric interfaces. If the metal film is prepared with holes or periodic corrugation, then diffracted light can be coupled to both LSPR and SPPs. Controlled engineering of the geometric parameters like height and periodicity of corrugation affect the strength and spectral position of LSPR, changing the metal film thickness changes the height of the extraordinary transmission (EOT) peak, and light-SPP coupling can be changed by altering the dimensionality and refractive index contrast in the attached photonic layer. In this study, we report for plasmonic interference coupling (PIC) where the plasmonic electromagnetic (EM) enhancement is critically dependent to the optical interference in the metal-insulator-metal (MIM) structure. The basic structure consists of the top metal with nanopores as a plasmonic layer and the bottom metal as an optical mirror. By controlling the thickness of the dielectric insulator at the middle, the optical interference patterns (i.e. constructive or deconstructive interference) were alternated at the top nanopore layer, thus resulting in great effects on surface-enhanced Raman scattering (SERS) responses. Therefore, we could clearly understand that such a MIM structure should be well designed by considering PIC characteristics to effectively utilize a plasmonic EM enhancement. We used nonporous anodic aluminum oxide (AAO) and titanium dioxide templates for accomplishing such a PIC structure. Furthermore, low-cost aluminum was applied to create non-uniform nanopore AAO and compared their optical properties with those of uniform AAO-based PIC structures (i.e. high-cost template). Finally, we could confirm scalable cost-effective PIC structures. Our results might provide the suitable design way for the applications of enhanced EM on plasmonic-integrated devices.