Nanogap Plasmon Resonator: An Analytical Model

Generic, analytical equations are suggested for the localized plasmon excited in a narrow gap formed between a metal/dielectric cylinder and a metal surface. The local distribution of the electric field was found by employing the quasi-static approximation. A strong electric field can be achieved in the nanogap in the optical and infrared frequency regimes. The maximum electric field was reached when the incident light was in resonance with the mode of the plasmon gap and can be expressed in terms of the incident field E0 as Emax/E0 proportional to epsilon m delta-2 with delta=I epsilon m/R epsilon m. This aspect of the maximum field achievable in the nanogap can be enhanced by many orders of magnitude. The results of the analytical model were in relatively good agreement with a known theoretical model and the experimental results of surface-enhanced Raman scattering (SERS). The narrow gap resonator seems to be a powerful and flexible tool for different spectroscopies such as SERS and infrared absorption.