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Science Technology

Reflectivity Reaches a New Low 166

sporkme writes "A new nanocoating material developed by a team of researchers from Rensselaer Polytechnic Institute has the lowest level of reflectivity ever seen ... or not seen in this case. The amount of light reflected by the composite of silica nanorods and aluminum nitride is almost the same amount reflected by air. From the article: 'Schubert and his coworkers have created a material with a refractive index of 1.05, which is extremely close to the refractive index of air and the lowest ever reported. Window glass, for comparison, has a refractive index of about 1.45. Using a technique called oblique angle deposition, the researchers deposited silica nanorods at an angle of precisely 45 degrees on top of a thin film of aluminum nitride, which is a semiconducting material used in advanced light-emitting diodes (LEDs). From the side, the films look much like the cross section of a piece of lawn turf with the blades slightly flattened.' Suggested applications include increased efficiency in solar cells, more energy-efficient lighting and advances in quantum mechanics."
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Reflectivity Reaches a New Low

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  • by Anonymous Coward on Friday March 02, 2007 @06:27PM (#18212680)
    oh crap where did it go?
  • by Anonymous Coward on Friday March 02, 2007 @06:28PM (#18212692)
    Even more birds hitting windows!
  • by messerman ( 446251 ) on Friday March 02, 2007 @06:29PM (#18212710)
    ...move along.
    • Re: (Score:2, Funny)

      by StarfishOne ( 756076 )
      It must have taken a long time of reflecting to write that post ;)
    • by numbski ( 515011 ) *
      It's odd no one seems to have picked up on the posibility of invisibility (or near-invisibility as it were). When light doesn't get refected back, our eyes can't see things. Am I right? In the dark it would be nearly impossible to tell an item of this material is there, other than by context (ie, light reflects from surrounding items, but not the item in question...)
      • Re: (Score:3, Informative)

        by PitaBred ( 632671 )
        "The sky reflects back blue, but there's this strangely dark spot moving against it... shoot it!" Just because it doesn't reflect light doesn't mean that it also doesn't block light. In the dark, it'd be very hard to see an object, but it would be the strange completely black spot against the backlight if you ever saw it silhouetted against a light source. It'd be awesome if they could use this as an anti-glare coating on binoculars or something, though.
        • I didn't see where they were talking about different kinds of light. A lot of time when they talk about reflectivity, they are also concerned with ifrared and other part of the light spectrum like radar waves and all.

          And yes, I agree, not reflecting light is only part of the invisibility problem. The other part is getting light to pass through or around an object making it apear as if the object isn't there. However, In the case of search lights in the night sky or maybe infra red heat vision and maybe rada
      • "It's odd no one seems to have picked up on the posibility of invisibility (or near-invisibility as it were)... In the dark it would be nearly impossible to tell an item of this material is there, other than by context (ie, light reflects from surrounding items, but not the item in question...)"

        We picked up on the possibility, but got way ahead of you before we posted.
  • They made several layers with increasing refractive indices, so the RI of the outermost coating is close to air while that of the innermost coating is close to the material it coats. What's cool about this is that it cuts reflexion across the EM spectrum, it doesn't just trade off reflectivity in one part of the spectrum for that in another, like previous anti-reflective coatings have done. Unfortunately, it isn't transparent so it won't work as a coating for glass.
  • by Archangel Michael ( 180766 ) on Friday March 02, 2007 @06:31PM (#18212744) Journal
    Would this constitute "Transparent Aluminum?

    typed on "Keyboard, how quaint"
    • by Tackhead ( 54550 ) on Friday March 02, 2007 @06:41PM (#18212906)
      > Would this constitute "Transparent Aluminum?
      >typed on "Keyboard, how quaint"

      Naw, that ship was at least visible. How about something like that ship over there. I mean that... is really bad for the eyes... I mean you can hardly make out its shape... light just seems to fall into it!

      And the UI... I mean, it's the wild color scheme that freaks me. Every time you try to operate on of these weird black controls that are labelled in black on a black background, a little black light lights up black to let you know you've done it. And then it crashes into the sun! What kind of UI is this, Windows Aero?

    • by xrayspx ( 13127 )
      I think you gotta think more Hotblack Desiato (from Disaster Area). Just because it doesn't reflect light doesn't mean you can see through it, that's why in the picture it looks black. Imagine a ship made all of this stuff, the instruments, guages, everything.
  • So where did I put that new "low reflectivity" bottle of vodka? I can't seem to find it.
  • A substance the matches the deep cold black hearts of the Vista activation process designers.
  • by drinkypoo ( 153816 ) <martin.espinoza@gmail.com> on Friday March 02, 2007 @06:34PM (#18212788) Homepage Journal
    How does reducing reflection increase the efficiency of LEDs? This stuff absorbs light. It seems to me like it would only be able to make things darker, not lighter. I'm willing to accept I just don't get it... but what is it that I don't get?
    • by 140Mandak262Jamuna ( 970587 ) on Friday March 02, 2007 @06:54PM (#18213038) Journal
      I did not read either the summary or the fine article, from what I heard on NPR, this coating improves the signal to noise ratio of communications. Sort of like talking in an anechoic chamber versus a room with highly sound reflective walls with booming echos.

      This is how I would explain it. All these reflections are really echos of light. And when a pulse of light is fired along the fiber, it gets reflected at many interfaces, travel backward, gets reflected again and travels forward etc. Thus the single transmitted pulse arrives as multiple pulses of varying strengths and varying time differences. When a series of pulses are fired, at somepoint the echos completely overwhelm the signal. The anechoic coating will help communication, stealth aircraft etc. It might find applications in improving solar cell efficiency. But might not make your light bulb any brighter.

      • The anechoic coating will help communication, stealth aircraft etc.

        Being stealthy involves reflecting back just enough to not be suspicious. Too much or too little and it's obvious that something of interest is there.

        Military contractors came up against this problem when designing stealth missiles that were supposed to skim the waves. Radar reflects off the waves & creates a certain amount of noise, but the first batch of missiles reflected nothing... which showed up as a moving black spot on the radar.

        • Being stealthy involves reflecting back just enough to not be suspicious. Too much or too little and it's obvious that something of interest is there.

          That wouldn't apply to aircraft though. There isn't something blocked by the airplane that reflects a radar signal. You wouldn't be able to identify the difference between the non-reflective air vs. the non-reflective aircraft using a normal radar.

          In theory, you could set up something where the radar emitter is on the opposite side of the aircraft from

    • From what I understand this coating doesn't absorb light; it's a transparent material that simply reflects less, and therefore transmits more.
    • Re: (Score:3, Insightful)

      by XenoRyet ( 824514 )
      I think the trick is that it's transparent, and non-reflective in the sense that nearly all the light goes through it unimpeded. As opposed to it being opaque, and non-reflective in the sense that all light gets absorbed.
    • by shawnce ( 146129 )
      Reducing reflection doesn't mean that the material absorbs more light... it just reflects less. Glass for example reflects some amount of the light (visible) that hits it while allow a majority of the rest pass thru it.
    • by K-Man ( 4117 )
      The efficiency of an LED die is limited by how many photons actually get out of the material and into the open air (if they don't, they reflect internally and turn into heat). Many of the recent improvements in LED efficiency have come about through better light transmission, which requires a careful transition from the high-index-of-refraction die to low-index-of-refraction air.

    • by njh ( 24312 )
      Every time light moves from one refractive index to another some light is reflected:
      http://en.wikipedia.org/wiki/Fresnel_equations [wikipedia.org]

      This coating moves the light more smoothly from air's RI (1) to say window glasses (1.45) and avoids the reflections.

      LEDs are made from an optically dense material (plastic) and lose a portion of their light due to internal reflection and reabsorption in the plastic or on the internal structure. I don't think it is the main source of inefficiency of LEDs though.
  • I wonder if they thought about doing this with radar instead of light- even sneakier stealth planes
    • Try painting your car with this stuff, drive past a cop shooting LIDAR, and see if you get pulled over.

      FWIW, police officers are trained to aim the LIDAR at your front license plate for best results, as the retroreflective surface provides the best return. However, this can be tricky with a moving target Of course, anything that provides a sufficient reflection will usually work.

  • Oh my... (Score:3, Funny)

    by keeboo ( 724305 ) on Friday March 02, 2007 @06:40PM (#18212888)
    Reflectivity Reaches a New Low

    Just when you started to think it couldn't get worse...
  • How much would it cost to cover your car with this?
  • Link to abstract (Score:4, Informative)

    by kmac06 ( 608921 ) on Friday March 02, 2007 @06:50PM (#18212968)
    Here's a link to the abstract [nature.com]. Don't think you can get the full article without some sort of subscription.

    Anti-reflection coatings are nothing new. Their used all the time in optics. What's new about this acts as a broadband anti-reflection coating. If this can be transferred to commercial production it would have a huge impact on optical equipment.
  • Probably extremely useful to military purposes. (ie. stealth sort of stuff)
  • Use for this stuff (Score:3, Interesting)

    by ksd1337 ( 1029386 ) on Friday March 02, 2007 @07:05PM (#18213134)
    I think they should coat television and computer monitor screens with this material. This will help to see the image being displayed, since there will not be any glare to obscure the image.
  • How strong is this stuff at greater thicknesses? Could it be used for better windows (less breakable, more transparent)?

    There are plenty of applications for high-strength high-transparency (which I'm assuming is a product of lower reflectivity) materials. Heck, if they're strong enough then depending on the cost there's a decent market for them just in the vehicle-window market (especially planes, jets, submarines, ships, etc).
  • The technique allows the researchers to strongly reduce or even eliminate reflection at all wavelengths and incoming angles of light,
    I'm amazed the article doesn't mention military applications. What do they use on stealth planes now?
    • I'm amazed the article doesn't mention military applications. What do they use on stealth planes now?
      They use a radar absorbing material, and a shape designed to refract radar mostly up and away from the ground.

      this material would do bupkus for Stealth. Radar would pass through, bounce off whatever else they make the plane out of, and then bounce right back to the receiver.

  • I use titanium dioxide enriched paint (white) as a topcoat on my projector screen.
    I wonder if the basecoat were of this material and the topcoat tiny (20 micron?) glass beads, would it give good results?
    I figure since the beads are round and the back of the display has no reflectivity, the light from the projector wouldn't bounce back and blind you like if you were to use a mirror because the back doesn't reflect...
    • Sans the new material, what you've described is a "lambertian" screen. Which despite its name is only approximately lambertian. Still it's quite useful for calibrating optics. (and would be very useful for your projector screen if it weren't so darned expensive.)
  • ... isn't the illusion of water on the road a product of light reflecting off of the air?
    • Sorry, wrong: (Score:5, Informative)

      by Ungrounded Lightning ( 62228 ) on Friday March 02, 2007 @07:54PM (#18213612) Journal
      ... isn't the illusion of water on the road a product of light reflecting off of the air?


      It's caused by the curvature of light refracted by the difference in refractive index between the hot air near the sun-heated surface and the cooler air above it. The light bends back up without "touching" the underlying surface.

      You only get a little bend. This is why you need a very hot surface to get enough of a bend to be visible at all. It's also why you only get it at large distances, where the line of sight is nearly parallel to the ground.

      It looks like water because you look at the ground and see a a region of like of the sky's color, shimmering due to convection current - generated patches of uneven refractive index in the air rather than surface ripples.
  • "Reflectivity Reaches a New Low"

    Those scumbags. Worse than the RIAA and MS combined!
  • I hereby nominate this nanocoating material for 'employee of the month'! (everyone has to win at least once)
    • "I hereby nominate this nanocoating material for 'employee of the month'! (everyone has to win at least once)"

      Then why have I been skipped twice?
  • I've always thought that nanotech was the new black -- now they're gone and proven me right :-)

    Of course, given that it's not descended from West African slaves, is it really black?

    http://www.rawstory.com/news/2007/Colbert_question s_Obamas_blackness_0209.html [rawstory.com] :-)

  • I am a manager at a large company. My employees always compliment me on how much they appreciate my open door policy. They can always walk in and ask me questions. Frankly, they're starting to annoy me! I can hardly get any work done.... I've only been able to play to level 2 of Tetris today and its a Friday!

    What is the possibility of making a transparent door with this new material? My open door policy will still remain in effect. But my door will always remain closed. I think I will like my job again when
  • Well.... (Score:3, Funny)

    by kaizenfury7 ( 322351 ) on Friday March 02, 2007 @07:50PM (#18213570)
    Me at a night club in the corner sipping my Jolt with my penguin shirt has even lower reflectivity. No one even knows I'm there. And that's with a _clean_ shirt even.
  • fun subject (Score:3, Funny)

    by nEoN nOoDlE ( 27594 ) on Friday March 02, 2007 @08:47PM (#18213976) Homepage
    Reflectivity Reaches a New Low

    Eh, until reflectivity wakes up in a dumpster with a dead hooker, not knowing how it got there or what happened the night before, I think it could get lower.
  • 'Cause I love non-visible light photography [naturfotograf.com] - but quartz lenses are a fortune - if you can find one.
  • The Nazis back in WW2 where doing all kinds of obscure military research. On of them being the search for the 'ultimate black' that would not reflect any light whatsoever and enable soldiers to appear as non-dimensional shadows. They didn't get very far iirc.
  • Now when you lose your marbles, they'll stay lost!


  • Aided by the Slashdot Einstein icon next to the story, I thought the title read, "Relativity reaches a new low," --and I eagerly read forth to discover what the heck kind of story could come with a heading like that.

    I was rather disappointed. Though I still like being able to say that it will now be so much harder to recover if you happen to lose your marbles.


  • From the TFA: A material that reflects no light is known as an ideal "black body." No such material has been available to scientists, until now.

    Hotblack Desiato will love this for his new stunt ship! After he's revived from spending a year dead - for tax purposes...

  • Just one question.

    "Black body radiation. The development could also advance fundamental science. A material that reflects no light is known as an ideal 'black body.' No such material has been available to scientists, until now. Researchers could use an ideal black body to shed light on quantum mechanics, the much-touted theory from physics that explains the inherent 'weirdness' of the atomic realm."

  • Great stuff... (Score:2, Interesting)

    by Moe Napoli ( 826364 )
    Now I can finally get around to painting all those faux holes like Wile E. Coyote.
  • This should be used to make bicycles and bicycle clothing in areas with a high population problem.

FORTUNE'S FUN FACTS TO KNOW AND TELL: A black panther is really a leopard that has a solid black coat rather then a spotted one.