Electric and Magnetic Field Enhancement with Ultralow Heat Radiation Dielectric Nanoantennas: Considerations for Surface-Enhanced Spectroscopies

Plasmonic structures are known to offer strong local enhancements of the electric field for interaction with molecules and materials in their vicinity. However, they inherently suffer from high losses and absorption, which can occur in both surface plasmon polaritons and localized plasmons in particles, on which we shall focus. An effect of those losses, and an aspect often neglected, is the local heating of the nanoparticle due to the absorption of incident radiation and the transduction into thermal energy. This increase in the nanoparticle temperature, and in turn in the surrounding medium, can directly disrupt the response of the system due to changes in the optical properties of the medium and nanoparticle itself. This is especially a problem in the spectroscopic analysis of matter, where the advantage of field enhancement due to the plasmonic effect can be obstructed (or hampered) by a local temperature increase affecting the pure electromagnetic response of the sample. Here we investigate the use of subwavelength structures made of high refractive index dielectrics with ultralow losses in the optical and near-IR regime, gallium phosphide (GaP) in this case, as a novel way to approach applications that require near- and far-field enhancement, such as surface-enhanced Raman spectroscopy, but with the peculiarity of not perturbing the response of the sample under evaluation due to local heating. In particular, we show a comparison of the near- and far-field enhancing performance of plasmonic dimers with the one obtained from similar structures made of GaP. This study opens new possibilities to overcome losses and heat generation issues associated with plasmonic nanostructures in a range of applications in nanophotonics and metamaterials.