Hyperbolic Metamaterials Fabricated Using 3D Assembled Nanorod Arrays and Enhanced Photocatalytic Performance

Abstract It is significant but challenging to develop a 3D colloidal assembly method for optical metamaterials. Hyperbolic metamaterials (HMMs) with 3D porous periodic morphologies are suitable for loading functional components for energy harvesting and biosensing and for providing a tunable range of indefinite permittivity. In this study, porous HMMs with 3D periodicities are constructed from directionally assembled silica nanorods with conformal coating of metal. The indefinite dielectric ranges around visible wavelength are formed from the anisotropic geometry induced anisotropic effective permittivity along different directions and are tunable according to the rod length, rod diameter, and thickness of metal coating. The negative refraction of rod array based metamaterials is verified using the transmission ratio between the part beam and full beam in microscope–spectrum system with incident light beam. The rod‐based metamaterials show a higher optical absorption in near‐ultraviolet and visible wavelengths than the compared colloidal sphere assembled structures. The porous HMMs loaded with TiO₂ can provide enhanced optical absorption and photocatalytic performances. The structures coated with 180–190 atomic‐layer‐deposition cycles of TiO₂ and 8–9 min deposition of silver provide the best performance.