"This material will increase the absorption efficiency of light, as well as the overall radiation-to-electricity efficiency of solar-energy conservation," said Shawn-Yu Lin, professor of physics at Rensselaer. He performed the work with Pulickel Ajayan, an engineering professor at Rice University who worked on the project at Rensselaer with Lin. Also contributing to the project were Rensselaer doctoral candidate Zu-Po Yang, Rice postdoctoral research associate Lijie Ci, and Rensselaer senior research scientist James Bur.

The darkest natural materials usually range from 5 to 10 percent reflectance. Many attempts have been made to engineer a material with zero reflectance, using liquids, solids and gases, but even the most successful materials composed of thin films of nickel-phosphorous alloy have from 0.16 to 0.18 percent reflectance. Lin's team, on the other hand, has been able to engineer the carbon nanotube-based material with just 0.045 percent reflectance--more than three times darker than the previous world's record.

The key, according to Lin, was loosely packing long, extremely porous vertically aligned carbon nanotube arrays. Nanotubes permit both low reflectance and high absorption to be achieved simultaneously, according to the researchers, because of the material's unique ability to custom tailor both the dimensions and periodicity of an array. By including a controllable degree of surface randomness with nanoscale gaps and holes that collect and trap light, the group was able to minimize reflection and maximize absorption to a degree never before achieved.

The team tested its material with a broad spectrum of light to show that its reflectance was constant over the entire range of visible wavelengths--resulting in a new material that is more than 100 times darker than standard glassy carbon, which uses the same chemical element as nanotubes.

The team predicts that engineers will be able to harness their discovery in applications such as solar panels, thermalphotovoltaic energy generators, infrared detectors and astronomical observatories.

Lin is a member of Rensselaer's Future Chips Constellation program, which engineers innovations in new materials and devices for solid-state lighting, sensing, communications, and biotechnology, with multidisciplinary teams of experts.

Lin's team has applied for a Guinness World Record as the world's darkest material.

The project was funded by the U.S. Department of Energy's Office of Basic Energy Sciences and the Focus Center New York for Interconnects.