New 'super-black' material absorbs light across multiple wavelength bands

Nov 09, 2011 by Lori Keesey
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. (Credit: Stephanie Getty, NASA Goddard)

(PhysOrg.com) -- NASA engineers have produced a material that absorbs on average more than 99 percent of the ultraviolet, visible, infrared, and far-infrared light that hits it -- a development that promises to open new frontiers in space technology.

The team of engineers at NASA's Goddard Space Flight Center in Greenbelt, Md., reported their findings recently at the SPIE Optics and conference, the largest interdisciplinary technical meeting in this discipline. The team has since reconfirmed the material's capabilities in additional testing, said John Hagopian, who is leading the effort involving 10 Goddard technologists.

"The reflectance tests showed that our team had extended by 50 times the range of the material’s absorption capabilities. Though other researchers are reporting near-perfect absorption levels mainly in the ultraviolet and visible, our material is darn near perfect across multiple wavelength bands, from the ultraviolet to the far infrared," Hagopian said. "No one else has achieved this milestone yet."

The nanotech-based coating is a thin layer of multi-walled carbon nanotubes, tiny hollow tubes made of pure carbon about 10,000 times thinner than a strand of human hair. They are positioned vertically on various substrate materials much like a shag rug. The team has grown the nanotubes on silicon, silicon nitride, titanium, and stainless steel, materials commonly used in space-based scientific instruments. (To grow carbon nanotubes, Goddard technologist Stephanie Getty applies a catalyst layer of iron to an underlayer on silicon, titanium, and other materials. She then heats the material in an oven to about 1,382 degrees Fahrenheit. While heating, the material is bathed in carbon-containing feedstock gas.)

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. (Credit: Stephanie Getty, NASA Goddard)

The tests indicate that the nanotube material is especially useful for a variety of spaceflight applications where observing in multiple wavelength bands is important to scientific discovery. One such application is 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.

In particular, the team found that the material absorbs 99.5 percent of the light in the ultraviolet and visible, dipping to 98 percent in the longer or far-infrared bands. "The advantage over other materials is that our material is from 10 to 100 times more absorbent, depending on the specific wavelength band," Hagopian said.

"We were a little surprised by the results," said Goddard engineer Manuel Quijada, who co-authored the SPIE paper and carried out the reflectance tests. "We knew it was absorbent. We just didn't think it would be this absorbent from the ultraviolet to the far infrared."

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.

Currently, instrument developers apply black paint to baffles and other components to help prevent stray light from ricocheting off surfaces. However, black paints absorb only 90 percent of the light that strikes it. The effect of multiple bounces makes the coating’s overall advantage even larger, potentially resulting in hundreds of times less stray light.

In addition, black paints do not remain black when exposed to cryogenic temperatures. They take on a shiny, slightly silver quality, said Goddard scientist Ed Wollack, who is evaluating the carbon-nanotube material for use as a calibrator on far-infrared-sensing instruments that must operate in super-cold conditions to gather faint far-infrared signals emanating from objects in the very distant universe. If these instruments are not cold, thermal heat generated by the instrument and observatory, will swamp the faint infrared they are designed to collect.

Black materials also serve another important function on spacecraft instruments, particularly infrared-sensing instruments, added Goddard engineer Jim Tuttle. The blacker the material, the more heat it radiates away. In other words, super-black , like the carbon nanotube coating, can be used on devices that remove heat from instruments and radiate it away to deep space. This cools the instruments to lower temperatures, where they are more sensitive to faint signals.

To prevent the black paints from losing their absorption and radiative properties at long wavelengths, instrument developers currently use epoxies loaded with conductive metals to create a black coating. However, the mixture adds weight, always a concern for instrument developers. With the carbon-nanotube coating, however, the material is less dense and remains black without additives, and therefore is effective at absorbing and removing heat. "This is a very promising material," Wollack said. "It's robust, lightweight, and extremely black. It is better than black paint by a long shot."


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User comments : 32

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Isaacsname
not rated yet Nov 09, 2011
Neat, I've often wondered if a material like this could eventually be engineered/modified/manufactured for thermoelectric applications ?
CapitalismPrevails
1.5 / 5 (8) Nov 09, 2011
If it efficiently absorbs all the light wavelengths, why can't it be used for solar power applications?
Mitchell
1 / 5 (4) Nov 09, 2011
If it efficiently absorbs all the light wavelengths, why can't it be used for solar power applications?


I am no expert, but I do know that there is only one type of Carbon that conducts electricity and that is Graphite, I don't think this is a Graphite.
antialias_physorg
5 / 5 (5) Nov 09, 2011
Solar power (PV) requires that an electron be pumped from a ground state into a free state where it can move about.

Absorption doesn't necessarily do that (only if the material has a band gap and then only for photons that have exactly that energy)

Other absorption is simply the elevation of electrons around an atom from a ground state into a higher state (for high energy radiation) or vibrations of bonds (for low energy radiation like infrared). Neither of these can be used in solar power applications (yet).
JRDarby
not rated yet Nov 09, 2011
If it efficiently absorbs all the light wavelengths, why can't it be used for solar power applications?


I am no expert, but I do know that there is only one type of Carbon that conducts electricity and that is Graphite, I don't think this is a Graphite.


I freely admit I could be wrong, but I think you mean "graphene," which is substantially different than graphite.
ArtflDgr
1 / 5 (4) Nov 09, 2011
so they created nano velvet...
has the same properties of regular velvet but more so...

antialias_physorg
5 / 5 (7) Nov 09, 2011
Both graphite and graphene conduct electricity very well. So do carbon nanotubes (though whether they behave as a semiconductor or more like a metallic material depends on the exact geometry of the tube)
BenjaminButton
5 / 5 (1) Nov 09, 2011
If you were to line the walls, floor and ceiling of a room with this material and hang a single buld from the ceiling...would you only see the bulb itself with a slight aura of light around it as the material would absorb all the rest?
Jeddy_Mctedder
1 / 5 (4) Nov 09, 2011
so this is basically science replicating the structure of polar bear fur/skin.
its about time.

next step, finding a way to grow it fast like polar bears do.
maybe even faster!
Nerdyguy
1.2 / 5 (5) Nov 09, 2011
If you were to line the walls, floor and ceiling of a room with this material and hang a single buld from the ceiling...would you only see the bulb itself with a slight aura of light around it as the material would absorb all the rest?


Presumably, though black paint would provide about the same effect(90% absorbent) vs. this coating (99%). Not a huge difference to the naked eye in a dark room. Big difference for instrument sensitivity though.
barakn
5 / 5 (4) Nov 09, 2011
With 9x times greater light bouncing off the painted walls vs. nanotube walls, "about the same effect" is not the phrase I would use.
Callippo
2.4 / 5 (12) Nov 09, 2011
"Super-black" sounds too racist for me. This material is not responsible for its color.
Ricochet
5 / 5 (1) Nov 09, 2011
so they created nano velvet...
has the same properties of regular velvet but more so...

The NEW favoured fabric of goths everywhere!
Nerdyguy
3 / 5 (8) Nov 09, 2011
"Super-black" sounds too racist for me. This material is not responsible for its color.


A) That was funny as hell!

B) What, no mention of cold fusion?
Nerdyguy
2.3 / 5 (6) Nov 09, 2011
With 9x times greater light bouncing off the painted walls vs. nanotube walls, "about the same effect" is not the phrase I would use.


At the age of 15 or so, a friend of mine with more liberal parents than I was used to was allowed to paint his entire room black. Ugly as sin. And, when there was only the one light on, you couldn't see diddly squat. Diddly squat being the technical term for 90% absorbent.
blackwater
not rated yet Nov 09, 2011
It should however have some applications in solar water and air heating. I wonder what the true % increase in efficiency might be with the 10% higher absorption....maybe that 10% would be from a hotter wavelength of light, i wouldn't know.
BlackRock_Shooter
1 / 5 (2) Nov 09, 2011
Material that's darker than black?

Now I've lost it.
QQBoss
5 / 5 (3) Nov 09, 2011
Time to update the old joke:

Quest: Why do New Yorkers only wear black?

Answ: Because they haven't found a darker color yet.

So when are the scientists going to try growing these nanotubes on a wearable substrate? The fashionistas will go wild!
Ethelred
1 / 5 (2) Nov 09, 2011
And that is four posts for the porn site spammer so that should be the end. Caught all within minutes of posting.

Report these guys. Its easy. Just hit REPORT ABUSE and give it a one so you know you did it.

Material that's darker than black?
fuligin.

http://en.wikiped..._New_Sun

Ethelred
ZachB
5 / 5 (1) Nov 09, 2011
Improved regulation of heat might make for a better space suit.

Is a skin tight space suit to much to ask for?
210
1 / 5 (4) Nov 09, 2011
"Super-black" sounds too racist for me. This material is not responsible for its color.

Neither are the people who are Black! Saying the material is black is scientifically consistent. Calling black people Black is high praise considering they are proud of being such and fought/fight hard for acceptance and relevance.
Now, I am not trying to put you down just do not want you to spend any time comparing science and fact with a civil issue. Peace, and...
word-to-ya-muthas
despinos
2 / 5 (4) Nov 10, 2011
It would be quite interesting to know where the absorbed radiation "goes" to. Is it all converted to heat in the CNTs layer and this heat emited? Do the CNTs go to excited states? Is there any kind of electromagnetic radiation emission (infrarred, UV, or other)?

A very nice application would be, for example, as a cover layer in non Photovoltaic sun pannels for water heating.

And something the reporter has probably missed: is this not a good anti-radar cover? :-) I can imagine setting up a company that applies a treatment (consisting of aligned CNTS layer) to cars that will render them "radar invisible".

I wonder if USA militars are already using this in their radar invisible airplanes...
ggrabowich
1 / 5 (1) Nov 10, 2011
Sounds like a perfect coating for a solar sail. 100% absorption sounds like it harvests the full energy of light and I imagine it might provide a reasonable amount of thrust in the vacuum of space at cryogenic temps if you have enough surface area.
Nerdyguy
1 / 5 (4) Nov 12, 2011
And something the reporter has probably missed: is this not a good anti-radar cover? :-) I can imagine setting up a company that applies a treatment (consisting of aligned CNTS layer) to cars that will render them "radar invisible".

I wonder if USA militars are already using this in their radar invisible airplanes...


Popular Science reported back in 2008 that the U.S. military was pursuing this for just such uses. The article below references it and the PopSci article.

Military Goes For Stealthy Kills With Ultra-Black Nanotubes
http://www.dailyt...id=10813
antialias_physorg
2 / 5 (1) Nov 12, 2011
Sounds like a perfect coating for a solar sail.

You'll want full reflectivity for a solar sail. Gives you double the impulse as compared to a perfectly absorbing one.
dglenn
not rated yet Nov 13, 2011
"Presumably, though black paint would provide about the same effect(90% absorbent) vs. this coating (99%). Not a huge difference to the naked eye in a dark room. Big difference for instrument sensitivity though."

If I've done the arithmetic right, 90% means about three and a half f-stops, and 99.5% means eight f-stops. Even though my eyes have much more dynamic range than any of my cameras, I'd still count that as a big difference to the naked eye. (But I'll concede that it's an even bigger difference to instruments, yes.)

I can't help wondering how durable this material is, and whether it would simplify some of my macro photography, for the times when I want the subject floating in a black background.
Yahp
not rated yet Nov 13, 2011
I can't help wondering how durable this material is


I don't know but I am afraid that this will be the most fragile surface imagninable. No scratch resistance whats-o-ever.
Dummy
1 / 5 (4) Nov 13, 2011
A very nice application would be, for example, as a cover layer in non Photovoltaic sun pannels for water heating.

And something the reporter has probably missed: is this not a good anti-radar cover? :-) I can imagine setting up a company that applies a treatment (consisting of aligned CNTS layer) to cars that will render them "radar invisible".

I wonder if USA militars are already using this in their radar invisible airplanes...

Brilliant deduction!
DigitalFreak
not rated yet Jan 02, 2012
I am not technically savvy as well almost any one here but isn't Radar detect by Radio Waves, Lidar uses Light, might be wrong, if I am let the slamming begin.
Callippo
1 / 5 (4) Jan 02, 2012
Popular Science reported back in 2008 that the U.S. military was pursuing this for just such uses.
How many time we will read about super black nanotubes?

http://en.wikiped...er_black

Apparently the physicists are wasting the money of tax payers in repetitive research, whereas the cold fusion research is waiting for decades.
despinos
3 / 5 (2) Jan 03, 2012
"I am not technically savvy as well almost any one here but isn't Radar detect by Radio Waves, Lidar uses Light, might be wrong, if I am let the slamming begin."

It's all electromagnetic waves of different lenght
DigitalFreak
not rated yet Jan 03, 2012
"I am not technically savvy as well almost any one here but isn't Radar detect by Radio Waves, Lidar uses Light, might be wrong, if I am let the slamming begin."

It's all electromagnetic waves of different lenght


Okay cool, I was not sure, the article did not mention anything about electromagnetic waves, just different wavelengths of light, was not sure if that applied to radio waves.