What is the darkest shade of black Vantablack took the world by storm for being the blackest black known to humankind. Its carbon nanotube surface—a nano-scale forest of billions of tiny carbon trees—absorbs up to 99.964% of light striking it. To witness such a dark material in person is beyond striking: It literally looks like a hole in reality itself, something so dark it feels like part of your soul is being sucked out through your eyeballs.
But while the rest of the world was being shocked by Vantablack, MIT scientists were discovering a black that bests it, along with every other ultra black discovered to date.
MIT’s new discovery, published in the journal ACS-Applied Materials and Interfaces, is technically 10 times darker than any other known black substance, a full order of magnitude darker than the blackest black we know. To mark the discovery, the authors worked with artist Diemut Strebe to coat a radiant, 16.78-carat yellow diamond in the stuff, titling this work of art Redemption of Vanity. The $2 million diamond is “the most brilliant material on earth, covered with carbon nanotubes, the most light-absorptive material (the blackest black on earth),” they write in a statement. “The literal devaluation of a $2 million diamond can be seen as a challenge to the art market and a statement on the arts by means of an aesthetic asceticism.” The piece is currently on display at the New York Stock Exchange (alongside a security guard, the exhibitors note).
The twist to the discovery is that the scientists responsible for creating the new blackest black weren’t even trying to do so in the first place. “We didn’t set out to create a black material!” says Brian Wardle with a self-effacing laugh. He’s the MIT professor of aeronautics and director at the school’s materials engineering necstlab who led the study. “It’s just a discovery.”
The team had been attempting to grow a layer of carbon nanotubes on a sheet of aluminum foil, in an attempt to increase the material’s thermal and electrical conductivity. (These sorts of qualities are prized in electronics and components like microprocessors.) Generally, growing nanotubes on aluminum is impossible, because an oxide layer on top of the metal, that’s present on most metals, blocks the process. MIT developed a workaround. It involved using saltwater to remove a thin, oxide layer on the aluminum (which prevents conductivity), corroding it away like an old ship sitting in the ocean. Then the foil was placed inside an oxygen-free oven (if oxygen were present, the oxide layer would simply reform on top of the aluminum) and baked at around 1,000 degrees with a source of carbon. Under these conditions, nanotubes grow right on the aluminum.
When the experiment worked, the researchers were left with a sheet of very, very, very black metal. But this wasn’t unusual, as Wardle explains.
“We grow a lot of different carbon nanotubes, and they’re all black,” says Wardle. “But at the time, we were working with an artist in the group [Diemut Strebe] who was interested mostly in the optical properties of the carbon nanotubes, which is not my expertise. When we did this new growth, it looked blacker than the normal black stuff, so we decided to measure it and see what it was.”
The lab tested the sample and learned it had inadvertently broken the ultra black record (which, incidentally, Warble clarifies was not held by Vantablack, but this “cupcake” configuration of carbon nanotubes).
Despite proof his lab’s black is the blackest, Wardle still cannot say why they broke the record. As he explains, nearly every ultra black we know is created by carbon nanotubes already—which can have wildly different configurations. There are 50 billion carbon nanotubes in every square centimeter of these samples. And there could be hundreds of unique shapes of nanotubes within that 50 billion-tube sample.
“The physics of where all the lights goes, and how it’s absorbed—there are several dominant mechanisms people have talked about—but if you dig into the review articles in literature, it’s not known why certain of these carbon nanotubes are blacker blacks than others,” says Wardle. “It’s [just] an empirical fact.”
Notably, this blackest black coating is not a paint; though the process of creating it is both inexpensive and scalable, any object you want shrouded must be able to withstand some pretty high temperatures inside an oven. The lab believes the discovery could have implications in solar-generated steam (energy), sensing near infrared frequencies, and astronomy equipment. But perhaps the best part of the discovery is that it wasn’t just science, or serendipity, that validated the finding.
“It’s pretty interesting that the artist in my group influenced the science,” says Wardle. “Without that collaboration, we wouldn’t have looked.”