Highly anisotropic multi-phase nanocomposite thin film for multifunctionality and tunability

Over the past few decades, metamaterials have attracted great research interest due to their extraordinary properties which cannot be easily achieved by natural materials. For example, anisotropic metamaterials that exhibit different properties along different directions, are valuable in different fields of optics. To achieve such anisotropic performance, nanocomposite designs by coupling different materials and functionalities have been demonstrated as an effective approach.

The goal of this dissertation is to design and fabricate anisotropic multiphase nanocomposite thin films with multifunctionality and tunability. Both transition metal oxides and transition metal nitrides are selected to study due to their high thermal stability, good crystallinity, and unique electromagnetic properties. In addition, different metals, especially plasmonic Au and magnetic Co, are selected as the metallic phase to fabricate nanocomposites. The designs also extend beyond the traditional two-phase nanocomposites to multiphase nanocomposites containing metal, oxide, and nitride, with more metamaterial design possibilities and more functionalities.

The dissertation consists of the introduction of multiphase nanocomposite thin film and experimental techniques, followed by four research chapters. In the first research chapter, hyperbolic HfO₂-Au with tunable optical properties is fabricated and studied. In the second research chapter, the magnetic Co is introduced into the nanocomposite thin film for multifunctionality design, and the obtained ZrO₂-Co thin film exhibits both hyperbolic optical property and magnetic anisotropy. In the third research chapter, vertically aligned nanocomposite (VAN) design and multilayer design are combined to achieve a complete three-phase HfO₂-Au/TiN-Au multilayer nanocomposite. Such a complete structure can exhibit tunable optical response. In the fourth research chapter, the magnetic Co is combined with the superconducting NbN to explore more applications of such VAN design. Overall, the dissertation work demonstrates various approaches of anisotropic metamaterials designs using oxides, nitrides, and metals. Enhanced functionality and multifunctionalities are demonstrated. Future research is needed for incorporating these new metamaterials designs in optical devices and sensors.