The technology relies on a physics phenomenon called plasmonics. The researchers first coat a surface with a thin film of gold through a common process like evaporation. They then put down a few-nanometer-thin layer of polymer, followed by a coating of silver cubes, each one about 100 nanometers (billionths of a meter) in size.
When light strikes the new engineered surface, a specific color gets trapped on the surface of the nanocubes in packets of energy called plasmons, and eventually dissipates into heat. By controlling the thickness of the polymer film and the size and number of silver nanocubes, the coating can be tuned to absorb different wavelengths of light from the visible spectrum to the near infrared.
"What is so attractive about the film/nanocube system is its remarkable simplicity and flexibility," said David R. Smith, the James B. Duke Professor of Electrical and Computer Engineering at Duke. "The unique absorbing properties of the nanocubes can be predicted with straightforward formulas, making it easy to quickly determine recipes for surface coatings that provide desired spectral properties. The nanocube system eliminates, or at least vastly reduces, cost and manufacturing issues, so that we can focus on impacting exciting application areas such as photovoltaics or thermal coatings."
For an example of the latter, if you can control the colors of light that a material absorbs, then you can also control the wavelengths of light that it emits. By making the nanocubes larger to absorb wavelengths corresponding to thermal radiation, this technology could suppress or mask an object's natural thermal radiation, otherwise known as "black body radiation."
Coating photodetectors to absorb only specific wavelengths of infrared light would allow novel and cheap cameras to be made that could see different infrared colors.
"We haven't made the device that's actually going to take that energy and convert it to an electrical signal yet," said Akselrod. "That's going to be the next step.