Future Chips Constellation

Researchers at Rensselaer have created the darkest material ever made. Able to absorb more than 99.9 percent of lighting, the discovery could one day be used to boost the effectiveness and efficiency of solar energy conversion, infrared sensors, and other devices.

“It is a fascinating technology, and this discovery will allow us to increase the absorption efficiency of light as well as the overall radiation-to-electricity efficiency of solar energy conservation,” says Shawn-Yu Lin, professor of physics and a member of Rensselaer’s Future Chips Constellation, who led the research project. “The key to this discovery was finding how to create a long, extremely porous vertically aligned carbon nanotube array with certain surface randomness, therefore minimizing reflection and maximizing absorption simultaneously.”

The Washington Post called the material, which is a thin coating comprised of low-density arrays of loosely vertically aligned carbon nanotubes, “a Roach Motel for photons—light checks in, but it never checks out.” The newspaper covered the research in a front-page story titled “Their Deepest, Darkest Discovery.”

All materials reflect some amount of light. Scientists have long envisioned an ideal black material that absorbs all the colors of light while reflecting no light. So far they have been unsuccessful in engineering a material with a total reflectance of zero.

The total reflectance of conventional black paint, for example, is between 5 and 10 percent. The darkest man-made material, prior to the discovery by Lin’s group, boasted a total reflectance of 0.16 percent to 0.18 percent.

Lin’s team created a coating of low-density, vertically aligned carbon nanotube arrays that are engineered to have an extremely low index of refraction and the appropriate surface randomness, further reducing its reflectivity. The end result was a material with a total reflective index of 0.045 percent—more than three times darker than the previous record, which used a film deposition of nickel-phosphorous alloy. The research has been accepted by the Guinness Book of World Records.