UC Davis

Controlling light-matter interactions at the nanoscale is driving the next technological revolution. The deep subwavelength confinement of electromagnetic fields heavily depends on the optical response of the metallic materials, e.g., how light is transmitted, reflected, and absorbed. To meet the increasing demands for photonic devices with superior optical performance, we focuse on researching alternative materials ― AgAuPd alloys, Magnesium (Mg), and transition metal nitrides (TMNs) ― from fundamentals to applications with advanced nanoscale design, aiming at overcoming the limitations of conventional noble metals. Firstly, we overcome the pre-defined constraints for the optical properties in the monoatomic metal system by forming AgAuPd alloy nanostructures through a scalable solid-state dewetting process. In-depth analysis via in situ optical and ex situ surface characterizations reveals the dynamic interplay between optical responses and the material's chemical inter-diffusion, alongside localized surface plasmon resonance (LSPR) effects driven by morphological changes. This approach paves the way for engineered optical properties in material design for photonics. Secondly, to address the scarcity of noble metals and the growing issue of electronic waste, we explore Mg, an earth-abundant material with low optical loss in the UV-VIS range, for sustainable photonics. Its unique degradability in water via a green chemistry reaction enables the realizations of two transient photonic devices using Mg-based thin films: (i) broadband reflective color filters achieving vivid hues and angular-insensitivities up to 50 degrees, which vanish within ~40 seconds after immersion in water, thus protecting optical information, and (ii) superabsorbers incorporating absorbing a-Si and lossless SiO2 layers to exhibit a spectrally selective and tunable near-unity resonant absorption, covering the primary RGB and CMY color spaces. We also propose the on-demand tuning of visible wavelengths by etching Mg nanostructures to attain a smooth transition of hues in color display devices for dynamic color displays. Thirdly, we challenge the optical behavior of TMNs, such as hafnium nitride (HfN), titanium nitride (TiN), and zirconium nitride (ZrN), at extreme environments for high-temperature applications. Our results show that TMNs exhibit gradual color changes through the controlled oxidation of 20-40 nm surface material at 600 °C, enabling their use in thermal color printing. Additionally, protective coatings with AlN and Al2O3 help to minimize unwanted oxidation, enhancing durability and maintaining optical performance at temperatures up to 800 °C. Overall, we foresee our results expanding the current library of optical materials and contributing to the design of photonic devices with improved optical and functional properties.