Refractory Metals and Oxides for High-Temperature Structural Color Filters

Abstract

Refractory metals have recently garnered significant interest as options for photonic applications due to their superior high-temperature stability and versatile optical properties. However, most previous studies only consider their room-temperature optical properties when analyzing these materials’ behavior as optical components. Here, we demonstrate structural color pixels based on three refractory metals (Ru, Ta, and W) for high-temperature applications. We quantify their optical behavior in an oxygenated environment and determine their dielectric functions after heating up to 600 °C. We use in situ oxidation, a fundamental chemical reaction, to form nanometer-scale metal oxide thin-film bilayers on each refractory metal. We fully characterize the behavior of the newly formed thin-film interference structures, which exhibit vibrant color changes upon high-temperature treatment. Finally, we present optical simulations showing the full range of hues achievable with a simple two-layer metal oxide/metal reflector structure. All of these materials have melting points >1100 °C, with the Ta-based structure offering high-temperature stability, and the Ru- and W-based options providing an alternative for reversible color filters, at high temperatures in inert or vacuum environments. Our approach is uniquely suitable for high-temperature photonics, where the oxides can be used as conformal coatings to produce a wide variety of colors across a large portion of the color gamut.

Plasmonic Titanium Nitride Nanohole Arrays for Refractometric Sensing

“…Group IVB, VB, and VIB metal nitrides are highly doped semiconductors, possess conductivity owing to free electrons from partially overlapping 3d and 2p orbitals, and exhibit plasmonic properties. Especially, group IVB metal nitrides (TiN, zirconium nitride, and hafnium nitride) exhibit a gold color and real part of (ε 1 ) similar to the permittivity of Au with a higher imaginary part (ε 2 ). , The most intriguing property of TMNs is, in fact, highly tunable dielectric permittivity through metal/nitrogen stoichiometry. , TMNs have remarkably high melting temperatures and show exceptional thermal stability; thus, TMN-based plasmonic devices are suitable for hot electron, photonic, and photothermal applications. – These materials also show exceptional mechanical durability , and chemical resistance to oxidation . TMNs display full-visible colors, highly reliant on the nanostructure’s physical shape .…”

“… 4 , 18 TMNs have remarkably high melting temperatures and show exceptional thermal stability; thus, TMN-based plasmonic devices are suitable for hot electron, photonic, and photothermal applications. 18 – 20 These materials also show exceptional mechanical durability 2 , 18 and chemical resistance to oxidation. 19 TMNs display full-visible colors, highly reliant on the nanostructure’s physical shape.…”