Two-Scale Structure for Giant Field Enhancement: Combination of Rayleigh Anomaly and Colloidal Plasmonic Resonance

Abstract

We propose a two-scale architecture by simultaneously exploiting both the Rayleigh anomaly and localized surface plasmon resonance in colloidal directly assembled oligomers to achieve giant field enhancement, overcoming limitations by losses and the intrinsic nonlocality of the dielectric response of metal nanoparticles. We show that the total field enhancement in the nanogap hot-spots of this two-scale structure is the product of the enhancements of each individual geometrical scale. Under this scheme, chemically assembled metallic oligomers enable strong enhancement of the near-field in resultant few-nanometer gaps at their plasmonic resonance. An extra enhancement factor results by combining the plasmonic resonance enhancement of these oligomers (nanometer scale) with a Rayleigh anomaly caused by a 1-D periodic set of nanorods (micrometer scale) fabricated using a lithographic method. This extra field enhancement cannot be obtained by further reducing the nanoantennas gaps, since they are already in the few nm ranges thanks to direct chemical assembly of oligomers. Experimental results verify that surface-enhanced Raman spectroscopy (SERS) signal is enhanced by more than one order of magnitude due to the Rayleigh anomaly as compared to the signal taken by using only metallic oligomers without periodic nanorods. The proposed two-scale structure could serve as a substrate for different spectroscopy techniques including SERS and can improve the sensitivity of spectroscopy for ultrasensitive biomolecule detection and single molecule spectroscopy studies.

Large-area flexible nanostripe electrodes featuring plasmon hybridization engineering

“…Additionally, thanks to the highly periodic lateral arrangement of the plasmonic nanostripes, it is possible to engineer coherent light scattering from the array into sharp optical modes (Rayleigh anomalies) peaked at wavelengths related with the pattern periodicity. The spectral overlap of such dispersive propagating modes with the LSP resonances of the NS monomers or dimers strongly amplifies the local electromagnetic field [42] and qualifies the transparent electrodes also as multifunctional templates featuring enhanced photon harvesting in the NIR spectral range with possible applications ranging from nanospectroscopy and biosensing to photovoltaics. In these experiments we employed Au as the active plasmonic element due to its chemical stability towards oxidation and tarnishing, as well as, to its excellent electrical conductivity.…”