Nanorod orientation dependence of tunable Fano resonance in plasmonic nanorod heptamers.

We present orientation dependence and tuning of Fano resonances in plasmonic gold nanorod heptamer nanostructures. The heptamer structures were formed by surrounding a central circular nanoparticle by six satellite nanorods in a hexagonal arrangement and the heptamer structures were then embedded in a thin flexible membrane. The Fano resonance was found to depend on the orientation of the nanorods within the heptamer and for a given orientation, the Fano resonance was dynamically tuned and its symmetry lowered by application of uniaxial mechanical stress. The expected spectral features were obtained by simulations and verified by experiments. The spectral features of the heptamer structures were further characterized by using detailed group theoretical analysis. We show that both sub-structural and mechanical tuning could be employed to engineer the Fano resonances in complex plasmonic molecules.