The material is made from vertically aligned carbon nanotubes (CNTs) - microscopic filaments of carbon - grown on a surface of chlorine-etched aluminum foil. The foil, say the researchers, captures at least 99.995% of any incoming light, making it the blackest material on record.
The material is showcased as part of an art exhibit featuring a 16.78-carat natural yellow diamond - estimated to be worth $2 million - coated with the new, ultrablack CNT material (see image). Practical applications, say the researchers, could include use as optical blinders that reduce unwanted glare, such as to help space telescopes spot orbiting exoplanets.
"There are optical and space science applications for very black materials," says Brian Wardle, professor of aeronautics and astronautics at MIT, "and of course, artists have been interested in black, going back well before the Renaissance. Our material is ten times blacker than anything that’s ever been reported, but I think the blackest black is a constantly moving target. Someone will find a blacker material, and eventually we'll understand all the underlying mechanisms, and will be able to properly engineer the ultimate black.”
The material was found by accident while the researchers were experimenting with ways to grow carbon nanotubes on electrically conducting materials, such as etched aluminum, to boost their electrical and thermal properties. While the combination of CNTs on aluminum significantly enhanced the material's thermal and electrical properties as expected, the researchers say they were surprised by the material's color.
"I remember noticing how black it was before growing carbon nanotubes on it, and then after growth, it looked even darker," says former MIT postdoc Kehang Cui and co-author of a paper on the research. "So I thought I should measure the optical reflectance of the sample."
Cui measured the amount of light reflected by the material - not just from directly overhead, but also from every other possible angle. The results showed that the material absorbed