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NIST Takes Carbon Nanotubes to the Really ‘Dark’ Side

by Editor1 last modified August 23, 2010 - 20:23

National Institute of Standards and Technology (NIST) researchers may have succeeded in using carbon nanotubes to create the world’s darkest material – one that will be key to a new generation of high-performance optics, lasers, communications and solar energy.

NIST Takes Carbon Nanotubes to the Really ‘Dark’ Side

NIST’s sparse "forest" of fine carbon nanotubes that coat a laser power detector.

The NIST team used a sparse array of fine nanotubes as a coating for a thermal detector, a device used to measure laser power. The CNTs reflect practically no light across the visible and part of the infrared spectrum.

In specific, the NIST detector uniformly reflects less than 0.1 percent of light at wavelengths from deep violet at 400 nanometers (nm) to near infrared at 4 micrometers and less than 1 percent of light in the infrared spectrum from 4 to 14 nm.  The coating absorbs laser light and converts it to heat, which is registered in pyroelectric material (lithium tantalate in this case). The rise in temperature generates a current, which is measured to determine the power of the laser. The blacker the coating, the more efficiently it absorbs light instead of reflecting it, and the more accurate the measurements.

NIST’s work is unique in that the nanotubes were grown on pyroelectric material, whereas other groups working on similar CNT projects grew them on silicon. Thanks to the use of pyroelectric medium, NIST researchers plan to extend the calibrated operating range of their device to 50 or even 100 micrometer wavelengths, to perhaps provide a standard for terahertz radiation power.

The configuration resembles a ‘forest,’ according to reports and uses vertically aligned multi-walled nanotubes rather than flat nanotube mats. The new orientation creates ‘deep hollows,’ reports said, which may help trap light, and the random pattern diffuses any reflected light in various directions.

NIST researchers were inspired by a 2008 paper by Rensselaer Polytechnic Institute (RPI) on "the darkest man-made material ever."