Rice researchers make a dark discovery A dark discovery — no, really, this stuff is dark

Professor Pulickel Ajayan, left, and Ligie Ci have created the darkest substance on Earth. The material could be used for collecting solar energy or improving telescopes, Ajayan said. Professor Pulickel Ajayan, left, and Ligie Ci have created the darkest substance on Earth. The material could be used for collecting solar energy or improving telescopes, Ajayan said. Photo: BILL OLIVE, FOR THE CHRONICLE Photo: BILL OLIVE, FOR THE CHRONICLE Image 1 of / 1 Caption Close Rice researchers make a dark discovery 1 / 1 Back to Gallery

In the iconic movie This is Spinal Tap, lead guitarist Nigel Tufnel said of his band's black album cover, "It's like, how much more black could this be? And the answer is none. None more black."

He was wrong.

A scientist at Rice University has created the darkest material known to man, a carpet of carbon nanotubes that reflects only 0.045 percent of all light shined upon it. That's four times darker than the previously darkest known substance, and more than 100 times darker than the paint on a black Corvette.

"The final numbers, when we measured how dark this material was, were more dramatic than we thought," said Pulickel M. Ajayan, a professor of engineering at Rice University who led the team that developed the substance.

The work was published last week in the journal Nano Letters.

Pure carbon is one of nature's darkest materials, as is clear to anyone who has seen charred organic materials such as wood.

But to further darken their material the scientists had to make the surface even rougher, to enhance the scattering of light. They struck upon a carpet-like arrangement of nanotubes standing on their ends.

The nanotubes, so named because they are tiny, are made solely of carbon atoms. Hollow cylinders with thin walls, the nanotubes used by Ajayan measure about one-hundredth of an inch long. They are very narrow, however, as their length is about 300,000 times their width.

It took more than a year of careful experimentation to determine that such a small fraction of light is reflected by this carpet-like forest of nanotubes, Ajayan said.

The previous record-holder was an alloy of nickel and phosphorus pitted with tiny craters developed in 2003 by researchers at the National Physical Laboratory in London. The material reflected about 0.16 percent of light shined upon it.

A dark spot in history

Ajayan said his team has applied to Guiness World Records . Developing a dark material is an easier way to gain admittance to the book than, say, eating 36 cockroaches in a minute, which Ken Edwards of England did in the year 2001.

"For me, yes," Ajayan said. "But I can't speak for every person."

The new material has some potential applications.

As it absorbs nearly all light, Ajayan said it could be useful in the collection and storage of solar energy.

Also, as it minimizes the scatter of stray light, it could improve optical instruments such as telescopes.

But for Ajayan, the aim is purely one of scientific discovery.

"There's a fundamental joy in such a fascinating study," he said.

eric.berger@chron.com