Darkest manmade material developed

Washington, January 23 : A team of researchers from Rensselaer Polytechnic Institute and Rice University has created the darkest material ever made by man-a thin coating comprised of low-density arrays of loosely vertically-aligned carbon nanotubes.

The researchers say that the material absorbs more than 99.9 per cent of light, and may one day be used for boosting the effectiveness and efficiency of solar energy conversion, infrared sensors, and other devices.

They have even applied for a Guinness World Record for developing this material.

"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," said Shawn-Yu Lin, professor of physics at Rensselaer and a member of the university'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," he added.

Every material, be it water, air, or plastic, reflects some amount of light. All efforts to make an ideal black material that absorbs all the colours of light while reflecting no light have so far proved futile.

The darkest manmade material, prior to the discovery by Lin's group, boasted a total reflectance of 0.16 percent to 0.18 percent. It was created with a film deposition of nickel-phosphorous alloy.

Lin's team created a coating of low-density, vertically aligned carbon nanotube arrays engineered to have an extremely low index of refraction and the appropriate surface randomness, further reducing its reflectivity. This enabled them to create a material with a total reflective index of 0.045 percent, more than three times darker than the previous record.

"The loosely-packed forest of carbon nanotubes, which is full of nanoscale gaps and holes to collect and trap light, is what gives this material its unique properties. Such a nanotube array not only reflects light weakly, but also absorbs light strongly. These combined features make it an ideal candidate for one day realizing a super black object," Lin said.

Upon testing the array over a broad range of visible wavelengths of light, the researchers found that its total reflectance remains constant.

"It's also interesting to note that the reflectance of our nanotube array is two orders of magnitude lower than that of the glassy carbon, which is remarkable because both samples are made up of the same element - carbon," said Lin.

This discovery, reported in the journal Nano Letters, may lead to applications in areas like solar energy conversion, thermalphotovoltaic electricity generation, infrared detection, and astronomical observation.

ANI