Microstructure and plasmonic behavior of self-assembled silver nanoparticles and nanorings

Self-assembled nanoparticles were formed after annealing ultrathin Ag films, which were grown on glass and quartz by direct current magnetron sputtering, in a furnace in air at 420 °C, 500 °C, or 600 °C. Intense localized surface plasmon resonances were observed for these samples in the entire range of visible light spectrum depending on the annealing time and nanoparticle size. Prolonged annealing resulted in the formation of nanorings and the change of the position and shape of resonances. The nanoring formation is attributed to partial evaporation of silver due to trapping of electromagnetic field by the larger nanoparticles despite the relatively low annealing temperature. Finally, in order to gain a further physical insight, the experimental results are compared with respect to rigorous theoretical calculations.