Nav: Home

Thermally-painted metasurfaces yield perfect light absorbers for high-tech applications

February 20, 2019

20 February 2019

WASHINGTON -- Researchers have discovered that the ancient technique of heating metal to create vibrant colors creates a nanostructured surface that acts as a perfect light absorber. Perfect light absorbers -- materials that absorb more than 99% of a certain color -- can be used for sensing, solar panels, anti-counterfeiting and stealth technologies.

In the journal Optical Materials Express, researchers from Case Western Reserve University in Ohio report their insights into how colors are generated on heated metal surfaces and apply those findings to create a nickel thin-film that perfectly absorbs red light.

"We found that a 3,000-year-old metallurgy technique is actually one of the simplest examples of a metasurface -- artificial surfaces with subwavelength features that impart unique electromagnetic properties," said Giuseppe Strangi, a member of the Case Western Reserve University research team. "Creating color changes by depositing a single metal layer opens up new aesthetic possibilities in metalworking, as well as applications such as shielding devices from electromagnetic signals that cause noise and interference."

Unlike the iridescent colors of water bubbles and butterfly wings, which change depending on the viewing angle, the thin oxide films produced by heating metal maintain their colors at all angles. This could make the heat-induced color useful for making holograms to protect currency and metal products from counterfeiting.

A simple approach

Scientists have previously demonstrated perfect light absorption using ultrathin absorptive materials on metals or with highly-engineered nanostructures. However, these materials require at least two material depositions using nanolithography fabrication methods that are expensive, time consuming and hard to reproduce.

"We showed that perfect light absorption could be realized using a simple thin-film with the right combination of oxide and metallic substrate," said Strangi. "This combination naturally occurs with certain metals like the nickel and titanium we used in this study."

To demonstrate their technique, the researchers deposited 150 nanometers of nickel or titanium on silicon and then heated the films for 20 to 40 minutes at 400 ?C to form an oxide layer. Analysis of the samples' absorption properties showed that the nickel films baked for 40 minutes absorbed approximately 99.94% of red light. The researchers also demonstrated that the light absorption could be tuned across visible and near-infrared wavelengths by modifying the heating duration, which changes the thickness of the oxide layer.

How it works

Perfect light absorption occurs in the heated metal because light rays emerging from the oxide layer and the metal substrate come together in such a way that they cancel each other out - a phenomenon known as total destructive interference. Any remaining light is absorbed inside the metal substrate.

"This method of creating perfect absorption is very practical due to its simplicity and reproducibility," said Strangi. "The oxide layer makes the surface scratch resistant and protects it from further oxidation."

The researchers plan to perform additional experiments to determine if high-resolution patterns can be formed by growing metal oxide layers. They are also working to develop gas sensors using the perfect light absorbers.
-end-
Paper: T. Letsou, M. ElKabbash, S. Iram, M. Hinczewski, G. Strangi. "Heat-induced perfect light absorption in thin-film metasurfaces for structural coloring," Opt. Mater. Express 9, 3, 1386-1393 (2019).

DOI: https://doi.org/10.1364/OME.9.001386.

About Optical Materials Express

Optical Materials Express (OMEx) is an open-access journal focusing on the synthesis, processing and characterization of materials for applications in optics and photonics. OMEx, which launched in April 2011, primarily emphasizes advances in novel optical materials, their properties, modeling, synthesis and fabrication techniques; how such materials contribute to novel optical behavior; and how they enable new or improved optical devices. The editor-in-chief for OMEx is Alexandra Boltasseva from Purdue University. For more information, visit: OSA Publishing.

About The Optical Society

Founded in 1916, The Optical Society (OSA) is the leading professional organization for scientists, engineers, students and business leaders who fuel discoveries, shape real-life applications and accelerate achievements in the science of light. Through world-renowned publications, meetings and membership initiatives, OSA provides quality research, inspired interactions and dedicated resources for its extensive global network of optics and photonics experts. For more information, visit osa.org.

Media Contact:

mediarelations@osa.org

The Optical Society

Related Color Articles:

Recovering color images from scattered light
Engineers at Duke University have developed a method for extracting a color image from a single exposure of light scattered through a mostly opaque material.
Deciphering how the brain encodes color and shape
There are hundreds of thousands of distinct colors and shapes that a person can distinguish visually, but how does the brain process all of this information?
Fish-inspired material changes color using nanocolumns
Inspired by the flashing colors of the neon tetra fish, researchers have developed a technique for changing the color of a material by manipulating the orientation of nanostructured columns in the material.
Iridescent color from clear droplets
Under the right conditions, ordinary clear water droplets on a transparent surface can produce brilliant colors, without the addition of inks or dyes.
Comparing antioxidants levels in tomatoes of different color
Greater levels of specific antioxidants were associated with particular colorations of tomato fruit.
More Color News and Color Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...