Nano-gap plasmonics: a bridge to the quantum realm
Metals support surface plasmons at optical wavelengths and have the ability to localize light to sub-wavelength regions. Nano-gap
plasmonic systems-in which two or more metallic nanoparticles are separated only few nanometer from each other by an insulating
spacer-have unique properties that make it useful for a variety of processes depending on the nanoparticle shape. Nanospheres that are
coupled to a film, for example, have been predicted to produce enormous field enhancements-as much as thousands of times that of the
incident radiation-in the separating region between nanoparticle and film. For the narrowest (<1 nm) gaps, light can be so tightly
confined that the nonlocality associated with the dielectric response of the metal and quantum effects can have a strong impact on the
scattering properties of the system, placing strict bounds on the ultimate field enhancement.