Morphology and Property Tuning in ZnO-Ni Hybrid Metamaterials in Vertically Aligned Nanocomposite (VAN) Form

ZnO thin films have attracted significant interests in the past decades owing to their unique wide band gap properties, piezoelectric properties, non-linearity and plasmonic properties. Recent efforts have been made in coupling ZnO with secondary phases to enhance its functionalities, such as Au-ZnO nanocomposite thin films with tunable optical and plasmonic properties. In this work, magnetic nanostructures of Ni are incorporated in ZnO thin films in vertically aligned nanocomposite form to couple magnetic and plasmonic response in one complex hybrid metamaterial system. Nickel (Ni) is of interest due to its ferromagnetic and plasmonic properties along with gold (Au) which is also plasmonic. Therefore, two approaches, namely, tuning of the vacuum pressure and use of a ZnO-Au seeding layer were attempted to achieve unique Ni nanostructures in addition to tuning of the microstructure. Together, both approaches demonstrated a range of microstructures such as core-shell, nanocup, and nanocube-like morphologies not previously attempted. Additionally, there was effective tuning of properties. Specifically, it was seen that the seeding layer thickness caused hyperbolic behavior as well as redshift in the surface plasmon resonance (SPR) wavelength. The addition of the ZnO-Au seeding layer directly influenced the optical properties. Plus, regardless of approach, the films demonstrated magnetic anisotropy based on the composition and microstructure of the film which impacted the saturation magnetization and coercivity. This study demonstrates the potential of ZnO-based complex hybrid metamaterials with coupled electro-magneto-optical properties for integrated photonic devices.