Michał P. Nowak¹, Tomasz Wojciechowski², Tomasz Stefaniuk³, Bartosz Bartosewicz¹, Przemysław Wachulak¹, Piotr Nyga^1
1Military University of Technology, Warsaw, Poland
²Institute of Physics of the Polish Academy of Sciences, Warsaw, Poland
³University of Warsaw, Warsaw, Poland
Structural color is a phenomenon commonly observed in nature, for example, the vivid hues of butterfly wings, and bird feathers. It originates from the interference of optical waves interacting with micro- and nanostructures on a surface. Unlike dyes and pigments, structural color is inherently durable and does not fade over time. It has found applications in the fabrication of artistic elements, document security features, camouflage, and optical filters.
Structural color can be generated through various mechanisms, including Fabry–Pérot (F-P) resonances in metal–insulator–metal (MIM) structures. In MIM structures, the perceived color depends on the spectral position and bandwidth of interference extrema, which can be precisely controlled by adjusting parameters of each layer, such as thickness and dielectric permittivity. An intriguing approach involves the use of a phase change material to achieve tunable structural color. Vanadium dioxide (VO₂) is especially well suited for this purpose. The refractive index of this material changes due to an isolator-metal phase transition triggered by temperature changes. The phase transition temperature of VO₂ is approximately 70 °C. Changes in the refractive index cause modification of the reflectance spectrum, which alters the perceived color.
In this work, we demonstrate two configurations of the Fabry–Pérot structure generating structural color based on (1) aluminum – silicon dioxide – aluminum and (2) VO₂ – silicon dioxide – aluminum. We report the influence of aluminum and vanadium dioxide layers' fabrication parameters on their optical properties and the resulting structural color. By employing aluminum layers with different dielectric permittivities, we were able to control the absorption level of the structures as well as the width of the reflection peaks in the F-P structures, thereby tuning the saturation of the observed colors. We also design a structure with VO₂ to achieve a wide range of actively controlled structure colors by temperature variations.
The fabricated structures exhibit high temporal stability, maintaining unchanged reflectance for over two years.