A team of scientists led by Duke University has designed a new material that produces tunable plasmonic properties while being able to withstand incredibly high temperatures.
Plasmon technology is a technique that essentially traps light energy in groups of electrons that oscillate together on a metal surface. This creates a powerful electromagnetic field that interacts with incoming light, enabling the device to absorb, emit or otherwise control specific frequencies across much of the electromagnetic spectrum.
The new material is hard enough to stir molten steel and can withstand temperatures in excess of 7,000 degrees Fahrenheit—roughly the same temperature as hundreds of miles above the surface of the sun. Combined with their newfound plasma capabilities, carbides could enable improved communications and thermal regulation in technologies including satellites and hypersonic aircraft.
The study was published online Oct. 11 in an open-access journal Nature Communications.
“Standard metals used in plasma research, such as gold, silver and copper, melt at relatively low temperatures and need to be protected from the elements,” says Arrigo Calzolari, a researcher at the Institute of Nanosciences at the Consiglio Nazionale delle Ricerche in Modena, Italy. This means they cannot be used in rockets, satellites or other aerospace applications. But these new materials we are developing open up a whole new field of work because they can generate plasmonic effects at extremely high temperatures.
These capabilities come from a class of disordered ceramics, called “high-entropy” carbides, discovered in 2018 by Duke University mechanical engineering and materials science professor Stefano Curtarolo. These high-entropy carbides do away with the reliance on the crystal structure and bonds that hold traditional materials together, relying on a combination of disordered elements of many different sizes to improve stability. While a pile of baseballs cannot stand on its own, a pile of baseballs, shoes, bats, hats, and gloves might support a resting baseball player.
The original group of high-entropy materials consisted of carbon and five different metallic elements, which are technically a class of carbides. Since then, Curtarolo has received a $7.5 million grant through the U.S. Department of Defense’s Multidisciplinary University Research Initiative (MURI) competition to develop a suite of artificial intelligence materials tools capable of designing similar materials with customized properties on demand.
Calzolari is aware of the material and the project that Curtarolo is leading. He also knew that tantalum carbide, a parent but simpler system, was very durable and exhibited plasmonic capabilities in the visible spectrum. But the material cannot be tuned to different frequencies of light outside its natural range, which limits its usefulness in practical applications. Putting two and two together, Calzolari and Curtarolo teamed up to have a hunch that certain formulations of high-entropy carbides—especially those containing tantalum—could exhibit tunable plasmonic properties over a wide range .
Less than six months later, they were proven correct.
“Arrigo came to me to make sure that these carbide mixtures would work and that they would have plasmonic properties,” Curtarolo said. “After running the recipe ideas through the disorder models and computations we’ve been developing, we found that they do have plasmonic properties, and we can tune them by tweaking the recipe.”
In the paper, the researchers’ model shows that 14 different high-entropy formulations exhibit plasmonic properties in the near-infrared and visible light spectra, making them good candidates for optics and telecommunications applications. They also collaborated with Douglas Wolfe, professor of materials science and engineering and head of the Metals, Ceramics, and Coatings Processing Division at Penn State’s Applied Research Laboratory, to demonstrate their theory experimentally.
As a member of the MURI project led by Curtarolo, Wolfe is already familiar with high-entropy carbides. He happened to have a sample of the relevant recipe, which helped the group quickly demonstrate the plasmonic properties of HfTa4C5 and show that they matched their computational model well.
The paper lists different compositions that work better or worse in different frequency ranges. The researchers plan to continue creating new formulations and testing their potential use in a wide range of applications, such as antennas, light and thermal manipulation, and more on any device that is subjected to ultra-high temperatures.
“These materials combine plasma, hardness, stability and high temperature into one material,” Curtarolo said. “And they can be tailored for specific applications, which is not possible with standard materials because you can’t change naturally defined properties.”
This work was supported by the Office of Naval Research (N00014-21-1-2132, N00014-20-1-2525, N00014-20-1-2299).
Materials provided Duke University. Originally written by Ken Kingery. Note: Content may be edited for style and length.