Optimal Interparticle Gap for Ultra-High Field Enhancement by LSP Excitation via ESPs and Confirmation using SERS Academic Article uri icon


  • We have predicted extremely high electromagnetic hot-spots using the extended-localized coupled surface plasmon resonance configuration, With this unique configuration, we found that an array of particles shows a critical importance of the inter-particle gap on the enhancement factor, which was confirmed experimentally using surface-enhanced Raman scattering (SERS). The extended plasmon wave excited in Kretschmann-Raether configuration propagates on the silver film surface and couples with the gold nanoparticles dispersed on top through the excitation of the localized plasmons. A monomolecular layer of 4-Aminothiophenol sandwiched in between the metal film and the nanoparticles showed SERS enhancement factor of the order of 1010 per molecule in the hotspots. The configuration was optimized, both by simulations and experiments, with respect to the size of the nanoparticles and the inter-particle distances. It is demonstrated that the ultra-high SERS enhancement does occur only when the ESP is coupled to the LSP at an optimized inter-particle gap. Further, highly sensitive detection of glycerol in ethanol is demonstrated using the optimum structure with detection limit of the order of 10-12 to the weight percentage of ethanol, which is equivalent to a few molecules detection. This ultrahigh enhancement is useful in realizing various highly sensitive biosensors when strong enhancement is required as well as in highly efficient optoelectronic and energy devices.

publication date

  • January 1, 2016