Estimating Near Electric Field of Polyhedral Gold Nanoparticles for Plasmon-Enhanced Spectroscopies

Technological application of polyhedral plasmonic nanoparticles (NP) is closely associated with their strong ability of localizing electric field at and near the surface. In this study, we calculate the optical properties of most common regular polyhedral Au nanoparticles such as the cube, rhombic dodecahedron, pentagonal bipyramid, and octahedron and compare with the optical properties of spherical particles to investigate the plasmonic behavior of metallic nanoparticles due to the breakdown of spherical symmetry. We demonstrate that the highest electric field enhancement (1 order magnitude higher than the spherical NP) occurs in octahedral Au NPs as the consequence of strong localization of incident electromagnetic field, decreasing the diffraction limit of the optical microscopies, which depends both on their size and orientation with respect to the polarization of incident light, increasing the system resolution. Higher order modes (quadrupole, hexapole, octupole, etc.) appear along the dipole mode as the shape of the NPs deviates from their regular spherical shape, even though their size remains much smaller than the incident wavelength. Irrespective of their shape, the major contribution of small NPs comes from the light absorption. Although the scattering efficiency of Au NPs becomes significant with the increase of their size, the NPs with sharper borders and vertices scatter higher fraction of light than the NPs of spherical shape.