Low-index metamaterials comprised of plasmonic dimers of aluminum-doped zinc oxide

摘要

Transparent conducting oxides (TCO) are an interesting class of plasmonic materials, which are under intensive study for their use in low-loss metamaterials and a range of applications such as sensing, imaging and transformation optics. Here, using both full-wave simulations and an equivalent circuit model for pairs of nanoparticles of aluminum doped zinc oxide (AZO), we study the plasmonic effects for low loss low index metamaterials for infrared applications. The behavior of localized surface plasmon resonances (LSPR) of AZO nanoparticle dimers embedded in a host polymer medium is investigated for different dimer orientations with respect to the indicent electromagnetic wave. In doing this, the role of dressed polarizability to enhance and quench the plasmonic effects is also considered. The effects of the nanoparticles relative size and the spacing between them are studied. Understanding these resonances and their dependence on dimer orientations, provides a means to design meta-material structures for use in the near infrared (NIR) region with epsilon-near-zero properties leading also to low index metamaterials. In our studies, we demonstrate how nanospheres with radii less than 100 nm that are distributed with an average spacing less than their diameter, can result in an effective medium with refractive index less than one. We utilize a full-wave frequency domain finite element method in conjunction with an equivalent-circuit model for the nanoscale dimers in order to describe the spectral response of the bulk low index properties. We also present a statistical analysis to obtain the effective refractive index for incident light having different polarizations.