The dazzling colors of peacock feathers arise from the physical interaction of light with biological nanostructures. In a new paper in Light: Science & Applications, researchers report exploiting this natural trickery, known as structural coloration, to develop a large-scale printing technology that produces lightweight and ultra-resistant coatings in any desired color.

Scientists routinely produce photonic structures to influence the behavior of light for applications such as fiber-optic communications. Many groups have used photonic technology to generate artificial structures that can take advantage of the entire spectrum of visible light. Moving this technology out of the lab has proved challenging, however, because photonic nanostructures are often fragile and difficult to produce in practical quantities.

Now, Andrea Fratalocchi from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, together with colleagues from Harvard University in the US and ETH Zurich in Switzerland, have used wet chemical techniques to help overcome the difficulties of scaling-up photonic colors. Inspired by the nanoporous feathers of the plum-throated cotinga bird, the team's approach begins by sputtering a platinum-aluminum based alloy onto a target surface. They then utilize a process called dealloying to dissolve most of the aluminum and induce the remaining metal to reorganize into a bumpy network featuring open nanopores.

"Controlling these colors is experimentally very simple and uses coating technologies that are cheap and easily implemented. However, understanding how the complex light-matter interactions generate colors took months of work."Andrea Fratalocchi, KAUST

Next, the researchers deposit an ultra-thin layer of protective sapphire onto the metal network to both protect the surface and modify the way in which light interacts with the photonic nanopores. Surprisingly, they found that slight changes in the thickness of the sapphire layer, varying from 7nm to 53nm, yielded remarkable color changes – the initially transparent film underwent stepwise transitions to yellow, orange, red and blue tones.

"Controlling these colors is experimentally very simple and uses coating technologies that are cheap and easily implemented," said Fratalocchi. "However, understanding how the complex light-matter interactions generate colors took months of work."

Using high-level simulations, the team determined that color generation begins when light strikes the metal and generates wave-like entities known as surface plasmons, which are then trapped by the randomly-distributed pores. This is a result of modulations in the coating's refractive index producing epsilon-near-zero regions in the nanopores that cause the waves to propagate extremely slowly. Adding the sapphire film causes additional reflections of the trapped waves, creating a flow of saturated color through resonance effects.

Fratalocchi noted that the way colors are produced by this structure opens the way for ‘programmable’ nanomaterials for many applications. "Imagine a scratch on a car that can be repainted with an extremely thin material without other expensive procedures, or as a lightweight, maintenance-free way to coat airplanes," he said. "This technology could be a real revolution."

This story is adapted from material from KAUST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.