Single particle dark-field spectroscopy of spherical dimers with down to sub-10 nm gaps fabricated by the annealing of nano-pillars

Abstract

In this paper we present a method for the fabrication of plasmonic spherical dimers and oligomers with narrow gaps and tunable distances. High-aspect-ratio nano-pillars are created by the two-step evaporation of gold on structured substrates. By using electron beam lithography, it is possible to control the close spacing of the pillars. Rapid thermal annealing causes the pillars to adopt a spherical shape. Since by melting the spheres gain in diameter compared to the initial nano-pillars, the distance between two adjacent spheres can be reduced to below 10 nm. Dimers with different distances were fabricated and optically characterized by single particle dark-field spectroscopy. The characteristic red-shift of the longitudinal mode due to stronger coupling for smaller distances could be clearly observed and follows a general scaling behavior.