Effect of non-alignment on nearfield coupling, charge density and sensitivity to the host medium of a gold nanorod homodimer

The impact of non-alignment on the plasmonic coupling parameters (resonance wavelength, nearfield intensity, charge density and sensitivity factor) between two gold nanorods is investigated by introducing a transverse shift (h) between the two resonators and then compared to the effect of the interparticle separation (g) on the same coupling parameters. FDTD electrodynamics simulation tool was employed to conduct such comparison. From the results of the simulations, it is found that as interparticle spacing increases, the above-monished parameters except charges density decay by second-order exponential function demonstrating the contribution from both multipolar and dipolar modes to the plasmonic coupling meanwhile the latter parameter drops sigmoidally with g following S-curve trend. As the two resonators are shifted transversely away from each other, both the resonance wavelength of the excited coupled mode and its corresponding sensitivity factor decay sigmoidally (S-curve trend) with h. The transverse shift-dependent behavior of the other two coupling parameters (charge density and nearfield enhancement factor) exhibits two-fold dependency on h. When h is less than the rod’s width, the fractional change of both charge density and field factor increases sigmoidally with h. As h exceeds the rod’s width, the fractional field factor drops with h and it follows a trend of a rational function meanwhile the fractional charges density decays exponentially with h. From the above findings, one can conclude that the coupling parameters observed in non-aligned resonators cannot be predicted by the proposed universal scaling (exponential) behavior in metallic homodimers.