Nanoengineering of conductively coupled metallic nanoparticles towards selective resonance modes within the near-infrared regime.

In this work, the mode transition effect of different plasmonic resonances in linked dimers by a conductive junction is numerically investigated.Without the junction, the dimer supports a single dipolar bonding plasmon mode, while two new resonance modes, a screened bonding dipolar mode and a low energy charge transfer plasmon mode, emerge when two nanoparticles are linked via a bridge. Such effect is proved to be unrelated to the shape of the nanoparticles, whether sphere, core-shell or nanoegg. However, it was found that the status of each specific resonance mode is profoundly influenced by the shape of nanoparticles. Furthermore, a detailed discussion of mechanisms of controlling plasmon modes, specially charge transfer mode, and tuning their corresponding spectra in bridged nanoparticles as functions of nanoparticle parameters and junction conductance is presented. These results show that the optical response of the dimer is highly sensitive to changes in the inter-particle gap. While the capacitive dimer provides a strong hotstop, the conductive dimer leads to highly controllable low energy plasmon mode at the mid-infrared region appropriate for novel applications. These findings may serve as an important guide for optical properties of linked nanoparticles as well as understanding the transition between the capacitive and conductive coupling.