Nav: Home

A new technique for structural color, inspired by birds

November 28, 2016

A peacock's bright teal and brilliant blue feathers are not the result of pigments but rather nanoscale networks that reflect specific wavelengths of light. This so-called structural coloration has long interested researchers and engineers because of its durability and potential for application in solar arrays, biomimetic tissues and adaptive camouflage. But today's techniques to integrate structural color into materials are time-consuming and costly.

Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in collaboration with King Abdullah University of Science and Technology, have developed a new, more robust and cost effective system to build large-scale metamaterials with structural color. The research is described in the journal Nature Light: Science and Applications.

A peacock's feather or butterfly's wing rely on photonic crystals or highly ordered arrays of nanofibers to produce colors. Reproducing those structures in a lab requires precision and expensive fabrication. SEAS researchers were inspired by a very different kind of feather.

Contingas are one of the most flamboyant bird families on the planet. In a sea of Amazon green, their feathers pop with electric blues, bright oranges and vibrant purples.

Unlike a peacock's ordered array of nanostructures, contingas get their vibrant hues from a disordered and porous nanonetwork of keratin that looks like a sponge or piece of coral. When light strikes the feather, the porous keratin pattern causes red and yellow wavelengths to cancel each other out, while blue wavelengths of light amplify one another.

"Usually, we associate the idea of disorder with the notion that something is uncontrollable," said Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior of author of the paper. "Here disorder can be put to our advantage and used as a design parameter to create a new class of metamaterials with a wide range of funcitionalities and applications."

Inspired by the cotinga feather, the researchers used a simple etching process to create a complex but random porous nanonetwork in a metallic alloy. The structure was then coated with an ultra-thin transparent alumina layer.

You may be thinking, what kinds of colors can a metallic alloy produce other than gray? As it turns out, lots. Ever since 19th century English scientist Michael Faraday, scientists have known that metals contain a plethora of colors but light doesn't penetrate deep enough to reveal them. A gold particle, for example, depending on its size and shape, can be red, pink or even blue.

The porous nanostructure creates localized hotspots of different colors in the alloy. The color that is reflected by the localized states depends on the thickness of the transparent coating.

With no alumina overlayer the material looks dark . With a coating 33-nanometers thick, the material reflects blue light. At 45 nanometers, the material turns red and with a coating 53 nanometers thick, the material is yellow. By changing the thickness of the coating, the researchers could create a gradient of colors.

"This situation is equivalent to a material with an extremely large number of microscopic and colorful sources of light," said Andrea Fratalocchi, corresponding author of the paper and Professor of Electrical Engineering; Applied Mathematics and Computational Science at the King Abdullah University of Science and Technology. "The presence of a thin layer of oxide can control the intensity of these sources, collectively switching them on and off according to the thickness of the oxide layer. This research shows of how disordered materials can be turned into an extremely powerful technology, which can enable large scale applications that would be impossible with conventional media."

The metasurface is extremely lightweight and scratch-proof and could be used in large-scale commercial applications such as lightweight coatings for the automotive sector, biomimetic tissues and camouflage.

"This is a completely new way to control optical responses in metamaterials," said Henning Galinski, co-first author of the paper and former postdoctoral fellow in the Capasso group. "We now have a way to engineer metamaterials in very small regions, which previously were too small for conventional lithography. This system paves the way for large-scale and extremely robust metamaterials that interact with light in really interesting ways."
This research is supported by the Airforce Office of Scientific Research.

Harvard John A. Paulson School of Engineering and Applied Sciences

Related Metamaterials Articles:

Researchers use metamaterials to create two-part optical security features
Researchers have developed advanced optical security features that use a two-piece metamaterial system to create a difficult-to-replicate optical phenomenon.
Artificial intelligence (AI) designs metamaterials used in the invisibility cloak
The research group of Prof. Junsuk Rho, Sunae So and Jungho Mun of Department of Mechanical Engineering and Department of Chemical Engineering at POSTECH developed a design with a higher degree of freedom which allows to choose materials and to design photonic structures arbitrarily by using Deep Learning.
Scientists take a 'metamaterials' approach to earthquake damage
At the SSA 2019 Annual Meeting, seismologists from around the world will discuss how metamaterial theory might be applied to everything from developing deflective barriers to manipulating the layout of buildings within a city as a way to minimize the impact of damaging surface seismic waves.
Fast and selective optical heating for functional nanomagnetic metamaterials
In a recent article published in Nanoscale, researchers from the Nanomagnetism group at nanoGUNE demonstrate the use of hybrid magnetic-plasmonic elements to facilitate contactless and selective temperature control in magnetic functional metamaterials.
Researchers 3D print metamaterials with novel optical properties
A team of engineers has developed a series of 3D printed metamaterials with unique microwave or optical properties that go beyond what is possible using conventional optical or electronic materials.
Intelligent metamaterials behave like electrostatic chameleons
Chinese physicists have developed so-called metashells made of smart, adaptable metamaterials.
Hyperbolic metamaterials enable nanoscale 'fingerprinting'
Hyperbolic metamaterials are artificially made structures that can be formed by depositing alternating thin layers of a conductor such as silver or graphene onto a substrate.
New concept for tractor beam from Star Wars developed
Physicists from ITMO University developed a model of an optical tractor beam to capture particles based on new artificial materials.
Physicists name and codify new field in nanotechnology: 'electron quantum metamaterials'
New materials are being synthesized by twisting and stacking atomically thin layers.
Where deep learning meets metamaterials
A new Tel Aviv University study uses 'deep-learning' computer networks inspired by the layered and hierarchical architecture of the human brain to design basic nanophotonic, metamaterial elements for energy harvesting and medical diagnostics.
More Metamaterials News and Metamaterials Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at