Team accidentally creates the darkest material yetSiobhan Treacy | September 19, 2019
Researchers from MIT have accidentally created the darkest black material yet. This material is 10 times darker than any previous black, capturing 99.995% of incoming light. It is made of vertically aligned carbon nanotubes (CNTs). CNTs are microscopic filaments of carbon grown on the surface of chlorine etched aluminum foil.
The team accidentally created the material while experimenting with ways to grow carbon nanotubes on electrically conducting materials. The goal of the project was to boost the electrical and thermal properties of the material. While attempting to grow CNTs on aluminum, the team ran into issues. They found that a layer of oxide will always coat the aluminum when it is exposed to air. This coating acts as an insulator, blocking heat and electricity. After trying multiple substances to eliminate the problem, the team landed on table salt, sodium chloride. The MIT team was already using other pantry products, like baking soda, to grow carbon nanotubes. When combining salt and aluminum, chlorine ions ate away at the aluminum surface, dissolving the oxide layer.
After the oxide layer was removed, carbon nanotubes could grow on aluminum at lower temperatures by 100° C. After being placed in a salt bath, the foil is transferred to an oxygen-free environment to prevent oxidization and placed in an oven. Once in the oven, nanotubes are grown through chemical vapor deposition. The combination of CNTs with the aluminum substrate enhances the material’s thermal and electrical properties, resulting in a material that is the darkest black created so far. The team believes the deep black is due to the combination of etched aluminum and carbon nanotubes.
Once they saw how dark this material was, the team had to test it to see exactly how dark it was. They measured the light that reflects off the material at every possible angle. They found that the material absorbed 99.995% of light, confirming that it was blackest material yet.
The team collaborated with Brian Wardle, professor of aeronautics and astronauts at MIT and artist-in-residence Diemut Strebe to create artwork using the black material. The artwork, called The Redemption of Vanity, is a 16.78-carat natural yellow diamond, worth $2 million, coated in the CNT material. This typically bright gem appears to be a flat black void.
There are many potential uses for the new material. It could be applied to optical blinds to reduce glare. Telescopes could use the material to help spot exoplanets. A paper on the material was published in ACS-Applies Materials and Interfaces.