  We report on the optical and physical characterization of metallic nanowire
(NW) metamaterials fabricated by electrodeposition of ~30 nm diameter gold
nanowires in nano-porous anodic aluminum oxide. We observe a uniaxial
anisotropic dielectric response for the NW metamaterials that displays both
epsilon-near-zero (ENZ) and epsilon-near-pole (ENP) resonances. We show that a
fundamental difference in the behavior of NW-metamaterials from
metal-dielectric multilayer (ML) metamaterials is the differing directions of
the epsilon-near-zero (ENZ) and epsilon-near-pole (ENP) dielectric responses
relative to the optical axis of the effective dielectric tensor. In contrast to
multilayer metamaterials, nanowire metamaterials exhibit an omnidirectional ENP
and an angularly dependent ENZ. Also in contrast to ML metamaterials, the NW
metamaterials exhibit ENP and ENZ resonances that are highly absorptive and can
be effectively excited from free space. Our fabrication allows a large
tunability of the epsilon-near-zero resonance in the visible and near IR
spectrum from 583 nm to 805 nm as the gold nanorod fill fraction changes from
26% to 10.5%. We support our fabrication process flow at each step with
rigorous physical and optical characterization. Energy dispersive X-ray (EDX)
and X-ray diffraction (XRD) analyses are used to ascertain the quality of
electrochemically deposited Au nanowires prior to and after annealing. Our
experimental results are in agreement with simulations of the periodic
plasmonic crystal and also analytical calculations in the effective medium
metamaterial limit. We also experimentally characterize the role of spatial
dispersion at the ENZ resonance and show that the effect does not occur for the
ENP resonance. The application of these materials to the fields of biosensing,
quantum optics and thermal devices shows considerable promise.
