ZnO-AuxCu1-x Alloy and ZnO-AuxAl1-x Alloy Vertically Aligned Nanocomposites for Low-Loss Plasmonic Metamaterials.

Hyperbolic metamaterials are a class of materials exhibiting anisotropic dielectric function owing to the morphology of the nanostructures. In these structures, one direction behaves as a metal, and the orthogonal direction behaves as a dielectric material. Applications include subdiffraction imaging and hyperlenses. However, key limiting factors include energy losses of noble metals and challenging fabrication methods. In this work, self-assembled plasmonic metamaterials consisting of anisotropic nanoalloy pillars embedded into the ZnO matrix are developed using a seed-layer approach. Alloys of AuxAl1-x or AuxCu1-x are explored due to their lower losses and higher stability. Optical and microstructural properties were explored. The ZnO-AuxCu1-x system demonstrated excellent epitaxial quality and optical properties compared with the ZnO-AuxAl1-x system. Both nanocomposite systems demonstrate plasmonic resonance, hyperbolic dispersion, low losses, and epsilon-near-zero permittivity, making them promising candidates towards direct photonic integration.

ZnO-ferromagnetic metal vertically aligned nanocomposite thin films for magnetic, optical and acoustic metamaterials.

Magnetoacoustic waves generated in piezoelectric and ferromagnetic coupled nanocomposite films through magnetically driven surface acoustic waves present great promise of loss-less data transmission. In this work, ferromagnetic metals of Ni, Co and Co x Ni1-x are coupled with a piezoelectric ZnO matrix in a vertically-aligned nanocomposite (VAN) thin film platform. Oxidation was found to occur in the cases of ZnO-Co, forming a ZnO-CoO VAN, while only very minor oxidation was found in the case of ZnO-Ni VAN. An alloy approach of Co x Ni1-x has been explored to overcome the oxidation during growth. Detailed microstructural analysis reveals limited oxidation of both metals and distinct phase separation between the ZnO and the metallic phases. Highly anisotropic properties including anisotropic ferromagnetic properties and hyperbolic dielectric functions are found in the ZnO-Ni and ZnO-Co x Ni1-x systems. The magnetic metal-ZnO-based hybrid metamaterials in this report present great potential in coupling of optical, magnetic, and piezoelectric properties towards future magnetoacoustic wave devices.