Superblack Material Absorbs Multiwavelengths of Light

A thin layer of multiwalled carbon nanotubes constitutes a new superblack material that absorbs 99 percent of multiple wavelengths of light — an achievement that promises to open new frontiers in space technology.

"Our material is darn near perfect across multiple wavelength bands, from the ultraviolet to the far-infrared,” said John Hagopian, who is leading the effort at NASA's Goddard Space Flight Center. “No one else has achieved this milestone yet.”

The nanotubes are positioned vertically on various substrate materials, and reflectance tests showed that the team had extended the range of each material's absorption capabilities by 50 times. They discovered that their superblack material absorbs 99.5 percent of the light in the ultraviolet (UV) and visible, dipping to 98 percent in the longer or far-infrared bands.

This close-up view (only about 0.03 inches wide) shows the internal structure of a carbon-nanotube coating that absorbs about 99 percent of the ultraviolet, visible, infrared and far-infrared light that strikes it. A section of the coating, which was grown on smooth silicon, was purposely removed to show the tubes’ vertical alignment. (Images: Stephanie Getty, NASA Goddard)

Hagopian noted that other researchers have reported near-perfect absorption levels mainly mainly in the UV and visible (See: Superblack Material Created).

“The advantage over other materials is that our material is 10 to 100 times more absorbent, depending on the specific wavelength band,” Hagopian said.

“We knew it was absorbent,” said Manuel Quijada, Goddard engineer. “We just didn't think it would be this absorbent from the ultraviolet to the far-infrared.”

The Goddard engineers originally reported their finding in August at SPIE’s Optics & Photonics 2011 conference in San Diego and have since reconfirmed the material’s absorption capabilities in additional testing.

This high-magnification image, taken with an electron microscope, shows an even closer view of the hollow carbon nanotubes. A coating made of this material is seen as black by the human eye and sensitive detectors because the tiny gaps between the tubes collect and trap light, preventing reflection.

The tests indicate that the carbon nanotubes are especially useful for a variety of spaceflight applications where observing in multiple-wavelength bands is important, such as in stray-light suppression. The tiny gaps between the tubes collect and trap background light to prevent it from reflecting off surfaces and interfering with the light that scientists actually want to measure. Because only a small fraction of light reflects off the coating, the human eye and sensitive detectors see the material as black.

If used in detectors and other instrument components, the technology would allow scientists to gather hard-to-obtain measurements of objects so distant in the universe that astronomers no longer can see them in visible light, or those in high-contrast areas, including planets in orbit around other stars, Hagopian said. Earth scientists studying the oceans and atmosphere also would benefit. More than 90 percent of the light Earth-monitoring instruments gather comes from the atmosphere, overwhelming the faint signal they are trying to retrieve.

Instrument developers currently use black paint to prevent stray light from ricocheting off surfaces, but the paint has only a 90 percent absorption rate and does not remain black in cryogenic temperatures, which are required for far-infrared-sensing instruments that gather faint signals from the distant universe. NASA is currently evaluating the carbon nanotube material for use on such instruments.

For more information, visit: www.nasa.gov/goddard