January 17, 2008
Darkest Material Known To Man Created
On Tuesday, U.S. researchers announced that they have made the darkest material on Earth, a substance so black it absorbs more than 99.9 percent of light.
The material, made from carbon nanotubes standing on end, is almost 30 times darker than a carbon substance used by the U.S. National Institute of Standards and Technology as the current benchmark of blackness. The material is close to the long-sought ideal black, which could absorb all colors of light and reflect none.
The team led by Dr Pulickel Ajayan, who is presently at Rice University in Houston, Texas, built an array of vertically aligned, low-density carbon nanotubes. Dr Shawn Lin measured the optical properties.
The roughness of the material's surface was tuned to minimize its optical reflectance.
"All the light that goes in is basically absorbed," Ajayan told Reuters in a telephone interview. "It is almost pushing the limit of how much light can be absorbed into one material."
Reporting their findings in the journal Nano Letters, Dr Ajayan, Dr Lin and colleagues say the reflectance of the material is three times lower than previously achieved. Basic black paint, by comparison, has a reflective index of 5 percent to 10 percent.
The researchers are seeking a world's darkest material designation by Guinness World Records. But their work will likely yield more than just bragging rights.
Ajayan said the material could be used in solar energy conversion. "You could think of a material that basically collects all the light that falls into it," he added. It could also be used in infrared detection or astronomical observation.00
Ajayan, who worked with a team at Rensselaer Polytechnic Institute in Troy, New York, said the material gets its blackness from three things. It is composed of carbon nano-tubes, tiny tubes of tightly rolled carbon that are 400 hundred times smaller than the diameter of a strand of hair. The carbon helps absorb some of the light.
These tubes are standing on end, much like a patch of grass. This arrangement traps light in the tiny gaps between the "blades."
The researchers have also made the surface of this carbon nano-tube carpet irregular and rough to cut down on reflectivity.
"Such a nano-tube array not only reflects light weakly, but also absorbs light strongly," said Shawn-Yu Lin told Reuters. Lin is a professor of physics at Rensselaer and helped make the substance. The researchers have tested the material on visible light only. Now they want to see how it fares against infrared and ultraviolet light, and other wavelengths such as radiation used in communications systems.
"If you could make materials that would block these radiations, it could have serious applications for stealth and defense," Ajayan added. The Indian-born Ajayan holds the 2006 Guinness World Record as co-inventor of the smallest brush in the world.
Commenting on the study, Professor Sir John Pendry, who first predicted that such a discovery might be possible, said the results were promising.
"They've made the blackest material known to science," the theoretical physicist from Imperial College, London, told BBC News. "The application will be to things like more efficient solar cells, more efficient solar panels and any application where you need to harvest light," he added.