The blackest material ever made

The blackest material ever made is a carpet of vertically oriented carbon nanotubes. The darkness or lightness of any object depends on the amount of light that gets reflected from it; as the object’s index of refraction n approaches unity, less light gets reflected. An ideal black object, having n = 1, absorbs all colors of light and reflects none of them. Developed by physicists at Rensselaer Polytechnic Institute (RPI) in Troy, New York, the vertically aligned carbon nanotube array has n less than 1.02 and a reflectivity of only 0.045%. As seen in the flash photograph, the VA-CNT’s reflectivity is 1/30 of the 1.4% NIST reflectance standard, three orders of magnitude lower than glassy carbon (a conventional black standard), and 1/3 of the previously darkest object (not shown). Shawn Lin and his colleagues grow the nanotubes on a prepared silicon wafer. The resulting mat, 10–800 microns thick, is light weight (0.01–0.02 g/cm³) and can be peeled off to become a freestanding film. The spaces between the nanotubes act like long pores that trap incident light, and the rough surface provides diffuse scattering. Both effects combine to produce the strong absorption. Possible applications of the film include a revised darkness standard and soaking up stray radiation in astronomical detectors or in photovoltaic cells. (Z.-P. Yang et al., Nano Lett. 8, 446, 2008.http://dx.doi.org/10.1103/PhysRevLett.8.446 )