Building Conventional Metasurfaces with Unconventional Interband Plasmonics: A Versatile Route for Sustainable Structural Color Generation Based on Bismuth

Plasmonic metasurfaces for structural color generation are typically built using the archetypal noble metals, gold, and silver. These possess plasmonic properties in the visible spectrum due to their inherent high free carrier densities. However, they are much more expensive compared to many other metals and exhibit several nanofabrication issues such as bad surface adhesion or thermally activated inter-diffusion. In this work, it is shown that interband plasmonic materials -whose optical properties are driven by interband transitions instead of free carriers- are appealing candidates for the fabrication of sustainable and cost-efficient metasurfaces for structural coloring. By using bismuth, an environment-friendly interband plasmonic material cheaper than gold and silver, nanodisks gap-plasmon metasurfaces and planar Fabry-Perot cavities are modeled and fabricated, which both successfully enable pure colors that can be robustly tailored upon suitable design. By direct experimental comparison between both types of design in terms of color efficiency, fabrication complexity, and angular robustness; how bismuth-based gap surface plasmon metasurfaces can be excellent candidates for color microprinting is shown, whereas nanolayered Bi Fabry-Perot cavities are ideal for macroscopic color coatings due to their ease of fabrication and implementation. They show how single-element, non-conventional interband plasmonic materials, such as Bismuth, can be successfully nanostructured toward the realization of both Gap-Plasmon-Metasurfaces and Fabry-Perot cavities for subtractive structural colors. It results demonstrate the potential of Bismuth as a reliable candidate for visible plasmonics, while inspiring the use of p-block materials as suitable plasmonic elements alternative to Au and Ag in the future.image