Tunable index metamaterials made by bottom-up approaches

Despite the exciting optical properties metamaterials exhibit, their implementation in nowadays technology is being hampered by the inherent losses of their metal constituents and the expensive and low-throughput used procedures. As an alternative, we present a new design of double fishnet metamaterials that can be easily realized combining two inexpensive and up scalable techniques: nanosphere lithography and metallic electrodeposition. A monolayer of polystyrene spheres is used as template for the infiltration of two symmetric gold layers separated by an air gap. The effective refractive index of the metamaterial can be easily tuned by the proper choice of the diameter of the spheres and the gap width between the metallic layers, varying its value from positive to negative. The good agreement between optical measurements and finite-difference time-domain simulations confirms the success of our process. Fishnet metamaterials with refractive index going from 1.5 until -1.0 in the near infrared range are demonstrated and the key parameters for these architectures provided.