Cascaded plasmon resonant field enhancement in nanoparticle dimers in the point dipole limit

Cascaded field enhancement in silver dimer nanostructures is investigated using a dipole-dipole interaction model. Field enhancement spectra are evaluated as a function of the particle size difference and inter-particle spacing. We observe three distinct regimes of cascaded field enhancement: hindered cascading, multiplicative cascading, and the ultimate cascading limit, depending on the dimer interaction strength. Multiplicative cascading at small inter-particle spacing leads to analytic expressions for the ultimate internal and external field enhancement factors. For silver dimers in a host with index 1.5, we obtain a maximum internal field enhancement of 2.9 10, a factor of 75 larger than that of an isolated silver nanoparticle. VC 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4707159]