Carbon nanotube forest camouflages 3-D objects

November 21, 2011
Scanning electron microscope images show a tank etched out of silicon, with and without a carbon nanotube coating (top row). When the same structures are viewed under white light with an optical microscope (bottom row), the nanotube coating camouflages the tank structure against a black background. Credit: L. J. Guo et al, University of Michigan/Applied Physics Letters

Carbon nanotubes, tiny cylinders composed of one-atom-thick carbon lattices, have gained fame as one of the strongest materials known to science. Now a group of researchers from the University of Michigan is taking advantage of another one of carbon nanotubes' unique properties, the low refractive index of low-density aligned nanotubes, to demonstrate a new application: making 3-D objects appear as nothing more than a flat, black sheet.

The of a material is a measure of how much that material slows down light, and "forests" have a low very close to that of air. Since the two materials affect the passage of light in similar ways, there is little reflection and scattering of light as it passes from air into a layer of nanotubes.

The Michigan team realized they could use this property to visually hide the structure of objects. As described in the AIP's journal , the scientists manufactured a 3-D image of a tank out of silicon. When the image was illuminated with white light, reflections revealed the tank's contours, but after the researchers grew a forest of carbon nanotubes on top of the tank, the light was soaked up by the tank's coating, revealing nothing more than a black sheet.

By absorbing instead of scattering light, carbon nanotube coatings could cloak an object against a black background, such as that of deep space, the researchers note. In such cases the carbon nanotube forest "acts as a perfect magic black cloth that can completely conceal the 3-D structure of the object," the researchers write.

Explore further: Carbon nanotubes show the ability to amplify light, could lead to new photonic applications

More information: "Low density carbon nanotube forest as an index-matched and near perfect absorption coating" is accepted for publication in Applied Physics Letters.

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not rated yet Nov 21, 2011
wouldn't a layer of CNT's be black, so wouldn't a coating of it obviously appear black under an optical microscope? its kinda like they painted it very black.
not rated yet Nov 21, 2011
I don't see a connection with tiny silicon tanks except maybe to appeal to DOD. Practically speaking, coating tanks would make them absorb heat.
not rated yet Nov 21, 2011
Mention deep space. If others know, and why would they not, of this, then we could be under surveillance from space by our stellar neighbors and we may never know it. Just have lots of 'hairy space ships'! No friction in space anyway.
not rated yet Nov 21, 2011
Well if they can make refractive index continuously variable, and not just low it could be possible to make some super low reflective coatings on optics. We don't want them absorbing though either.
not rated yet Nov 22, 2011
If others know, and why would they not, of this, then we could be under surveillance from space by our stellar neighbors and we may never know it.

Don't have to go that far. You can bet that the next generation of military spy sattelites will have this kind of coating.

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