Charge transfer plasmon resonances of conductively linked asymmetric gold nanoparticle dimers

Understanding a direct transfer of charges in bridged conductive nanodimers is a central research problem relevant for numerous applications including nanomotors, sensing and other optoelectronic devices. Here we investigate theoretically the tunability of charge transfer plasmon resonances (CTPRs) of bridged symmetric and shape-asymmetric gold nanodimers through varying the geometries of the bridging nanowire and refractive index of the surrounding medium. Unbridged symmetric dimer supports a single dipolar bonding plasmon mode, whereas two new resonance modes emerge in bridged shape-asymmetric dimers. In particular, due to the broken symmetry bridged shape-asymmetric dimer supports a sharp Fano-like resonance in the visible region. Varying the junction diameter and length of the bridging nanowire controls the resonance wavelengths and the scattering spectra of CTP modes. Increasing the diameter (length) of nanowire shifts CTP modes to considerably shorter (longer) wavelengths in the near and mid-infrared regions of the spectrum. Furthermore, the position of these resonance modes mainly depends on the refractive index of the environment, which will be useful for applications in molecular sensing. Similarly, the intensity of CTP modes can be modified by varying the aforementioned parameters. Furthermore, it was found that the CTP mode is extremely influenced by the geometries of bridged shape-asymmetric dimer. Finally, we explored the sensing applications of CTP with optimized geometries to evaluate the ability of CTP in the detection of refractive index. Hence, our designs provide extremely tunable CTP mode in the near and mid-infrared region, which are suitable for molecular sensing.