Polarization-Dependent Plasmon Coupling in Gold Nanoparticles and Gold Thin-Film Systems

Abstract

The characteristics of gap plasmon formed by nanoparticle-on-mirror (NPOM) structures composed of metal nanoparticles (MNPs) and metal thin films have aroused interest for use in various optoelectronic devices. The resonance enhancement characteristics in the gap region of an NPOM structure composed of gold nanoparticles and gold thin films are simulated theoretically by the finite element method (FEM). The resonant spectrum obtained by the internal coupling effect of the gap can be flexibly controlled by the polarization of incident light and the thickness of the dielectric layer between the MNPs and the metal thin films. We study the resonance spectra of polarization-dependent gold ellipsoidal nanoparticles (GENPs) and gold thin films in the gap region of an NPOM structure. The GENPs and gold thin films are separated by a dielectric layer with a refractive index of 1.36. We observe that the intensity of the resonance electric field in the gap region is inversely proportional to the polarization angle. Similarly, the intensity of the local electric field resonance peak in the gap region is inversely proportional to the thickness of the dielectric layer. When the thickness of the dielectric layer is 0.3 nm and the polarization angle is 0°, the best resonant electric field intensity of 2200 V/m is obtained in the gap region of the NPOM structure (the power of incident light is 1 mW). Finally, the resonant peak wavelength of the electric field in the gap region of the NPOM structure is also controlled by the polarization angle of the incident light and the thickness of the dielectric layer.