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Posted: January 15, 2008
Dark, dark nanotechnology
(Nanowerk News) An ideal black object absorbs all of the colors of light and reflects none of them. Researchers at Rice University have demonstrated a new concept based on a low-density nanotube array material that can be engineered to dramatically change an objectís index of refraction and nanoscale roughness, hence, its optical reflection.
An article in the Houston Chronicle puts it like this: "A scientist at Rice University has created the darkest material known to man, a carpet of carbon nanotubes that reflects only 0.045 percent of all light shined upon it. That's four times darker than the previously darkest known substance, and more than 100 times darker than the paint on a black Corvette."
A photograph of a 1.4% NIST reflectance standard, a CNT sample, and a piece of glassy carbon, taken under a flash light illumination. (Image: Nano Letters, American Chemical Society)
Arrays of vertically aligned carbon nanotubes are shown to achieve this goal by offering a mechanism for minimizing reflection that is fundamentally different from a traditional antireflection coating or surface roughening. The new degrees of freedom afforded by a nanotube array, such as independent control of tube diameter and tube-to-tube spacing in the 10-50 nanometer range, allow the creation of an extremely low reflectance material. The observed reflectance from the nanotube arrays is the lowest-ever reported reflectance from any material and could have applications ranging from solar energy conversion to pyroelectric detectors.