Scalable, Angle-Insensitive Structural Color Printing Using Refractory Metals for High-Temperature Applications

Structural color systems are growing in popularity due to their myriad of applications ranging from sensing to selective absorption. However, typical structural color devices require nanopatterning, which is difficult to scale up and can have negative environmental effects, or complicated many-layer geometries, which require multiple fabrication steps to achieve their vivid coloration. We utilize the oxidation of several sputtered refractory metal thin films at high temperatures (600°C) to produce four unique three-layer Fabry-Perot-type resonators which each offer vibrant colors with only two fabrication steps: MoO₃/Mo/Si (Purple), RuO₂/Ru/Si (Pink), Ta₂O₅/Ta/Si (Yellow), and WO₃/W/Si (Teal). These optical devices have the added benefit of being thermodynamically stable up to 700°C in an inert environment, making them ideal for high-temperature structural color applications. We heat these samples utilizing <i>in situ</i> ellipsometry, allowing very precise control over the thickness of the oxide layers <i>via</i> real-time sample characterization during high-temperature oxidation. In addition, we simulate the expected absorption spectra for different thicknesses of the two thin-film layers to determine the full range of colors each material combination can produce, showing that a wide area of the color gamut is accessible for these samples utilizing layer thicknesses of 10 – 100 nm. A detailed and quantitative analysis of the optical response of all refractory metals and their respective oxides will be presented. Our approach of using metals and dielectrics based on refractory metals offers a promising new avenue for structural color fabrication, requiring a single sputtering fabrication step that enable vibrant colors across a large portion of the color gamut.