Natural minerals for making cost-effective structural colors

Structural color coatings offer exceptional vibrancy and durability but remain limited in many applications due to high material costs and fabrication complexity. A new study demonstrates the fabrication of multilayer optical coatings using unprocessed natural mineral powders via electron beam evaporation to address the former limit. Published in Optics and Photonics Research, this research highlights a cost-effective pathway for producing optical coatings using minimally refined raw materials, with potential applications in photonics, optoelectronics, and sustainable color technologies.

Structural color coatings have drawn significant attention in the field of photonics due to their unparalleled vibrancy, outstanding durability, and environmental resistance. Unlike traditional organic pigments, these coatings produce color through light interference in stacked thin films, allowing them to withstand UV radiation, humidity, temperature fluctuations and chemical exposure. However, the widespread adoption of structural color coatings is currently limited by the high cost of refined starting materials and the vacuum-based deposition processes typically intended for electronic devices.

To address these economic and technical barriers, Professor L. Jay Guo from the University of Michigan has adopted a way demonstrating that natural minerals can be used directly to produce interference-based structural colors without prior refinement. The study explores the use of raw mineral powders, such as SiO₂, TiO₂, and iron/copper oxides (Fe₂O₃ and CuO) to deposit thin films that achieve the optical properties required for structural color coating. The researchers focused on the High-Low-Absorber (HLA) structure, which uses dielectric layers with distinct refractive indices to produce vibrant colors ranging from yellow to purple to green.

A key finding of the research is that electron beam evaporation encourages the distillation and purification of these natural materials during the deposition process. For example, the study notes that materials like scoria and blue topaz, despite containing impurities, produced SiO₂-like films due to the specific vapor pressure properties of silica.

To enable the coatings to be applied to arbitrary substrates like glass and plastic, the team developed a specific mixture of CuO and Fe₂O₃ powders. While these minerals were unstable individually, the mixture formed a stable film with metallic-like absorption and electrical conductivity. This innovation allows the structural color platform to expand beyond silicon wafers to more practical surfaces.

The research utilized advanced characterization techniques, including ellipsometry, X-ray photoelectron spectroscopy (XPS), and optical reflectance simulations, to validate the performance of the mineral-derived films. The results showed strong agreement between the simulated and measured structural colors, confirming that ceramic powders can yield optical-quality coatings with reproducible properties.

By combining the distillation effects of e-beam evaporation with the HLA design, this method establishes a scalable and sustainable route for producing structural color coatings with significantly reduced material costs and environmental impact.

This paper “Use of natural minerals toward cost-effective fabrication of layered structural colors by physical vapor deposition” was published in Optics and Photonics Research.
 

Rorem BA, Cheng Y, Guo L.J. Use of natural minerals toward cost-effective fabrication of layered structural colors by physical vapor deposition. Opt. Photonics Res. 2025(1):0002, https://doi.org/10.55092/opr20250002.