Symmetry-Dependent Plasmonic Properties of Three-Dimensional Hybrid Metallic Nanostructure Arrays

We demonstrate the successful fabrication of various well-ordered 3D gold nanostructure arrays using nanosphere lithography method, and further reveal the strong dependence of the optical responses on their in-plane symmetry. For the concentrically stacked ring-cap array, its optical absorption behavior is similar to that of a ring array with the same dimension because they have the same in-plane symmetry. However, for the nonconcentrically stacked hole-cap array, the broken in-plane symmetry results in the appearance of crescent-shaped nanogaps at the interfaces and thus leads to a novel strong plasmon resonance mode. The finite-difference time-domain simulation shows that charge mainly assembles to the sharp edges of the nanogaps at the resonant wavelength and remarkable electric field enhancement is achieved around the sharp edges. Furthermore, the strongest resonance modes of the ring-cap array and hole-cap array show large red shift as the nanostructure size increases. The presented 3D nanostructure ...