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 the critical importance of the interparticle gap on the enhancement factor, which was confirmed experimentally using surface-enhanced Raman scattering (SERS). The extended plasmon wave excited in the Kretschmann−Raether configuration propagates on the silver film surface and couples with the gold nanoparticles dispersed on top through excitation of the localized plasmons. A monomolecular layer of 4-aminothiophenol sandwiched between the metal film and the nanoparticles showed an SERS enhancement factor of the order of 1010 per molecule in the hot spots. The configuration was optimized, both by simulations and experiments, with respect to the size of the nanoparticles and the interparticle distances. It is demonstrated that the ultrahigh SERS enhancement does occur only when the extended surface plasmon is coupled to the localized surface plasmon at an optimized interparticle gap. Further, highly sensitive detection of glycerol in ethanol is demonstrated using the optimum structure with a detection limit on the order of 10−12 to the weight percentage of ethanol, which is equivalent to detection of a few molecules. 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.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Energy (all)
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films