With an ability to soak up 99.96 percent of the light that hits it, the material known as Vantablack has earned plenty of attention as the world’s blackest material, with scientists testing it in space and BMW using it to give its X6 SUV an eye-catching paint job. But MIT engineers are now claiming to have produced a material 10 times blacker than anything before it, an advance that could have useful benefits for space exploration in particular.
The new material actually came about by accident in a way, as MIT engineers led by professor of aeronautics and astronautics Brian Wardle were experimenting with the electrical conductivity of carbon nanotubes (CNTs) grown on materials such as aluminum. But in finding a solution to a problem they encountered along the way, the team may have inadvertently discovered a way to take ultra-black materials into even darker territory.
When attempting to grow CNTs on alumnium, which is actually how Vantablack and other ultra-black materials are produced together with chemical vapor deposition, the team kept finding layers of oxide forming as the aluminum was exposed to air. But by soaking the aluminum foil in saltwater before placing it in the oven to grow their CNTs, the team was able to avoid the oxide layer altogether.
Without the oxide layer to contend with, the team was then able to grow the carbon nanotubes on the aluminum at far lower temperatures than was possible before, at around 100° C cooler (180° F), to be precise. This brought about significant gains to the material’s thermal and electrical properties, which didn’t come as a surprise to the scientists. What did catch them off guard, however, was how dark the material seemed to be.
“I remember noticing how black it was before growing carbon nanotubes on it, and then after growth, it looked even darker,” says former MIT postdoc and study co-author Kehang Cui. “So I thought I should measure the optical reflectance of the sample.”
The team’s analysis looked at not just what the material was able to reflect when subjected to light from directly overhead, but from every possible angle. This revealed the material absorbed at least 99.995 percent of all light that hit it, significantly outperforming the light-absorbing capabilities of similar materials, including the much celebrated Vantablack.
“The published reflectivity of all the other superblack materials in the visible spectrum, and near IR and IR, are summarized in our paper, and our material can be seen to reflect 10 times less light across the visible spectrum at any given wavelength than the next least reflective material, and at least 10 times less than Vantablack based on their data,” Wardle tells New Atlas.
Understanding the exact mechanisms behind this new ultra-black material still requires more work, though the scientists suspect it is to do with the way these forests of carbon nanotubes trap light and convert it to heat. While it will take further investigation to pin down the exact reasons why, this new blackest of black materials is already generating a bit of interest in certain scientific communities.
For now, the team has demonstrated the material as a coating for a a US$2-million diamond, replacing its many facets and intricate detail with a lifeless black void. The clearest potential applications for these kinds of materials, however, lie in the realm of space exploration.
When telescopes and imaging instruments are turned toward distant celestial bodies for study, blocking out other light sources so they don’t pollute the field of view is an important part of the process. In 2016 we saw a version of Vantablack launched into space for testing aboard a satellite, and the new material developed at MIT could follow a similar path. Astrophysicist and Nobel laureate John Mather is one who is exploring using this new material in the construction of advanced shades that guard space telescopes from extraneous light.
“Optical properties of materials are not my group’s specialty, but I’ve spoken with numerous scientists about light trapping applications of black materials in optical instruments and lasers, in particular for improved effectiveness of star shades which aid in exoplanet identification and characterization,” says Wardle.
A paper describing the team’s research was published in the journal ACS-Applied Materials and Interfaces.
Source: MIT
