Plasmonic Oligomers With Tunable Conductive Nanojunctions

Plasmonic particles can be welded together, but controlling the metallurgy of the hotspots is a challenge in colloidal chemistry. In this paper, we demonstrate an original method that connects gold particles to their neighbors by another metal of choice. To achieve this goal, we first assemble gold bipyramids in a tip-to-tip configuration, yielding short chains of variable length. The good colloidal stability and surface accessibility make the nanochains suitable seeds to grow metallic junctions in a second step. We follow the oligomer formation and the deposition of the second metal (i.e. silver or palladium) via UV/Vis spectroscopy and we map the plasmonic properties of the nanostructures at nanometer scale using electron energy loss spectroscopy. The formation of silver bridges leads to a huge redshift of the longitudinal plasmon modes into the mid-infrared region, while the addition of palladium results in a redshift accompanied by significant plasmon damping.