Nanotech yields darkest material ever measured

Nanotech yields darkest material ever measured
Rice, RPI researchers file world-record claim for nanotube material

BY JADE BOYD
Rice News Staff

Researchers from Rice University and Rensselaer Polytechnic Institute have created the darkest material ever measured — a thin carpet of carbon nanotubes that’s four times darker than the previous record-holder.

JEFF FITLOW

Rice’s Lijie Ci (left) and Pulickel Ajayan and researchers from Rensselaer Polytechnic Institute have created the darkest material ever measured — a thin carpet of carbon nanotubes that’s four times darker than the previous record-holder.

The researchers who developed the material have applied for a Guinness World Record. They say the material could find use in super-efficient solar converters, telescopes and special coatings. The team’s results appeared this month in the journal Nano Letters.

“The low-density arrangement of the nanotubes is the key,” said study co-author Pulickel Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science. “We engineered the super-dark optical properties by tightly controlling the dimensions and spacing of the nanotubes.”

The carpet, which looks like a thin sheet of black paper, is made of billions of tiny hollow tubes of pure carbon that are vertically aligned like packaged spaghetti. The material’s darkness lies in the loose packing of the tubes. Because the tips of each nanotube measure just one-billionth of meter across, most light striking the surface is absorbed. As a result, the material reflects only 0.045 percent of the light that strikes it.

“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, the lead co-author on 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.”

By comparison, the darkest conventional black paint reflects about 100 times more light than the nanotube carpet. The previous record holder for darkest manmade material was a nickel-phophorus alloy whose surface was pitted with tiny, light-trapping craters.