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Carbon nanotube carpet darkest thing ever made

Scientists from Rice University and Rensselaer Polytechnic Institute figured out a way to trap light efficiently with nanotubes; 99.955 percent of the light that hits gets absorbed.

Michael Kanellos Staff Writer, CNET News.com
Michael Kanellos is editor at large at CNET News.com, where he covers hardware, research and development, start-ups and the tech industry overseas.
Michael Kanellos
2 min read

A loosely packed "carpet" of carbon nanotubes is the darkest material ever made, according to researchers from Rice University and Rensselaer Polytechnic Institute.

The carpet consists of nanotubes--hollow, honeycombed tubes made from carbon atoms-- standing vertically. Instead of being tightly packed together, the researchers went for a low density arrangement, complete with spaces and gaps, sort of like a box of dried spaghetti. Light striking the nanotubes as well as the gaps gets absorbed. When light gets absorbed, black (the absence of light) results. The nanotubes were also specially manufactured to have a more random arrangement of atoms, further reducing reflectivity. (Again, think of trying to look into a box of spaghetti. Not easy.)

The nanocarpet is in the middle. Former record holder to the left. RPI

This resulted in a material that reflects only 0.045 percent of the light that strikes it. (Put another way, 99.955 percent of the light that hits it gets absorbed.)

Conventional black paint reflects 100 times more light. The previous record holder for darkness, a nickel-phophorus alloy pitted with light-trapping craters, reflected four times as much light.

So what good is this? Will goths use it for Halloween costumes? The material could help in advancing solar cells, which trap sunlight and convert it to energy. It could also one day be used by astronomers.

Side shot of the nanocarpet RPI

Chalk another one up for carbon nanotubes, the reigning celebrity in the advanced materials world. Many believe the tubes will be used to deliver medicine in humans, build bridges, and conduct electricity inside of semiconductors someday.

"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 Rensselaer physicist Shawn-Yu Lin in a prepared statement. He's the lead co-author of the study. "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."