The key to the technology is atom-thick nanotubes. The tubes are arranged vertically on the surface, widely-spaced and standing on end, like the bristles of a paint brush. The key is the spacing. By widely spacing the tubes, light is able to enter the material, but then ends up trapped within the collection of thin tubes.
Project leader and Rensselaer physics professor Shawn-Yu Lin explains, “The loosely packed forest of carbon nanotubes, which is full of nanoscale gaps and holes to collect and trap light, is what gives this material its unique properties. Such a nanotube array not only reflects light weakly, but also absorbs light strongly. These combined features make it an ideal candidate for one day realizing a super black object.”
To give an idea of exactly how black the result is, black paint reflects approximately 5 percent of the visible light that strikes it. The previous darkest material was a nickel-phosphorous compound, which only reflected 0.35 percent of visible light. The new nanotube compound blows away these previous competitors, reflecting a bare 0.045 percent of the visible light that hits it. This is almost nine times less than the previous record holder and over a hundred times less than black paint.