Plasmonic Enhancement of Local Fields in Ultrafine Metal Nanoparticles

We present an analysis of ultrafine metallic nanoparticles (1-15 nm) with respect to electromagnetic field generation by plasmonic excitations. A number of structures with different symmetries and geometries are studied in order to analyze the distributions of plasmonically generated near-electric fields and the concentration of hot and cold spots around the particles. The study is made possible by the recent development of an extended discrete interaction model (Ex-DIM) where the explicit dependency of the plasmonic spectra on the structure and composition of particles in the range of 1-15 nm is accounted for. With the Ex-DIM, the optical response of the internal crystal structure of the nanoscale particles can be visualized, thereby making it possible to predict the dependence of the generated local fields with respect to the position of the particles relative to the external field polarization. The results indicate rather surprising concentrations of the plasmon fields in very confined hot spots also in cases when the particles retain a high symmetry. The consequence of the findings of this study when using small symmetric nanoparticles for near-field imaging is briefly discussed.