ACS Photon. (2017)

The strong enhancement of electromagnetic fields in small dielectric gaps between metal structures is one of the main attractive characteristics of plasmonics. However, limitations on the size of the enhancement arise due to fabrication capabilities and heat-related damage. Another phenomenon, Landau damping, is usually neglected as a limitation because it is assumed to be weak unless structural features are on the subnanometre scale. Now, Jacob Khurgin and colleagues from the USA and Taiwan, have theoretically considered the case of a metal dimer — two closely spaced metal particles with a dielectric gap — and found that the effect of Landau damping on field enhancement and distribution may be relevant for gaps as large as 2 nm or more, which is a feature size already achieved in experimental situations. For slightly smaller gaps, the effect may be drastic. For example, a dimer formed by two 2.5 nm gold particles spaced by a 0.5 nm gap yields a calculated surface damping rate (resulting from non-local modifications) that is two orders of magnitude larger than for bulk gold. This increased dissipation in turn reduces the maximum electromagnetic field enhancement by a similar order. The authors conclude that Landau damping actually may be the most practically relevant limit to plasmonic enhancement of electromagnetic fields.

Credit: American Chemical Society