You know how washing detergents can make your whites whiter than white? Well, now NASA’s Goddard Space Flight Center has made a black that’s blacker than black. Dubbed super-black, the material is fashioned out of carbon nanotubes and absorbs more than 99% of ultraviolet, visible, infrared, and far-infrared light, making it the perfect lining for telescopes and other incredibly sensitive instruments that are tasked with picking out a handful of photons from an entire universe of light pollution. Super-black could massively improve our ability to peer deep into the cosmos — and, perhaps more chillingly, enable the creation of stealth vehicles that are very, very good at evading detection.
Carbon nanotubes, as you may know, are hollow tubes of carbon. If you took a flat sheet of graphene and rolled it up, you’d have a carbon nanotube. In super-black’s case, we’re talking about multi-walled carbon nanotubes (MWNTs), which are essentially a bunch of nanotubes slotted concentrically inside each other, like a Russian Doll. Unlike single-walled carbon nanotubes (SWNTs), which have exciting electrical properties, MWNTs are of scientific interest due to their mechanical properties and their ability to absorb electromagnetic radiation. In essence, the gaps between each of the concentric tubes absorb and baffle any incoming photons. Almost no light is reflected, so no light hits your retina — and thus the material appears to be super-black. (See: Stanford builds first complex computer chip out of carbon nanotubes.
As an aside, MWNTs also absorb microwaves — and radar uses microwaves. It is for this reason that MWNTs are also being studied as an ideal coating for stealth vehicles. NASA is developing super-black for use in space exploration (of course), but being a governmental agency, it wouldn’t be surprising if super-black finds its way to the US military.
NASA had previously succeeded in growing super-black on flat pieces of silicon, but this wasn’t massively useful as most instruments consist of complex, rounded shapes such as tubes and baffles. To grow super-black on arbitrary shapes, NASA turned to atomic layer deposition (ALD), the same process being used by the chipmaking industry to progress to 22nm and beyond. Basically, to grow nanotubes on a surface, you first need to build up a catalyst layer of iron oxide — and ALD can be used to deposit an ultra-thin layer of iron oxide on objects of any shape or size. Then, in a process known as chemical vapor deposition (CVD), the oxide-coated object is baked it in an oven at 750 degrees Celsius (1,382F) in an atmosphere containing carbon (such as methane or acetylene). The oxide particles break apart the gas molecules, and the carbon atoms are ferried to the edges of the oxide particle, creating a nanotube. Control the conditions just right and you end up with an object covered in super-black.
NASA has now successfully coated intricately shaped objects with super-black, such as an occulter, which could be used in a new instrument for observing planets around other stars. Unfortunately, in the photo above, the occulter is pictured before its super-black coating has been applied. In the image at the top of the story, though, you can see that super-black is indeed very black.
Moving forward, the ALD/CVD process now needs to be refined so that it produces higher-quality super-black, and then NASA will probably push ahead with actually creating super-black-coated parts for future spacecraft. The most obvious candidate is the James Web Space Telescope (JWST), the Hubble successor that is planned to launch in 2018. When you’re peering deep into space, trying to pick up the weakest of signals from far away stars or alien civilizations, super-black could be a huge boon to science. For more information, watch the video embedded below.