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The RPI researchers made such a porous structure by depositing materials on a surface to create nanoscale rods. Tilting the surface makes it possible to grow the nanorods at an angle. The researchers found that by changing the angle of the nanorods, they can control the way the nanorods bend light--the index of refraction. Air has an index of refraction of very nearly one. The researchers were able to make a top layer of nanorods with what Schubert says is an unprecedented index of 1.05. (For comparison, glass has an index of refraction of 1.45, and a light-emitting semiconductor, aluminum nitride, has an index of about 2.05.) Each successive layer has a higher index of refraction until the last layer nearly matches the substrate. The top two layers incorporate glass nanorods. The bottom three are made of titania. The researchers tested the coating on aluminum nitride, but it should work on a variety of substrates, Schubert says.
"We have developed a new class of materials that has a refractive index that is lower than anything else--any other viable optical thin-film material that has been available in the past," Schubert says. Since "everything in optics depends upon the refractive index," he says it could have applications other than antireflective coatings. Indeed, the nanorods could be used to do the opposite, creating very highly reflective mirrors by pairing layers of nanorods that bend light very differently, rather than by creating a gradual transition.
Schubert is working with a spinoff company to commercialize the technology, and he anticipates that products could be available in three to five years. The technology will face competition with inexpensive conventional coatings as well as with other new nanostructured materials. "This is very elegant, beautiful work," says Michael Rubner, a professor of materials science and engineering at MIT. "They've been able to get some exceptionally low refractive-index values for a coating. The key question is always going to be cost versus performance."
Currently, solar cells loose efficiency when their surface is not normal to the direction of light. This new technique might eliminate the need to mechanically vary the angle of solar collectors throughout the day.
Re: Importance for Solar Cells
but the solar cells using this moth eye structure will cause the surface recombination. so account for all, this antireflection structure will not enhance the output efficiency though enhance the absorption.
Index tuned metamaterial (using moth eye effect)
Here is the info:
http://www.umass.edu/chm/tech_transfer/UMA0715.html
Today was finally the day that our solar panels were installed on our roof. We were very excited until our neighbors became up set at the reflection that they were getting through their kitchen window and they were worried about the reflections they would get in their yard in the summer. They are ready to go to the city to complain, we are very unhappy. They have always been great neighbors and we are just trying to do the best we can for ourselves as far as being able to afford to live in our home and pay the utility bills. If there is a coating that can give us more energy and give our neighbor less reflection, we really need it. Our installers say they have never had a problem like this. I've never seen our neighbors react like this. Has anyone else had to deal with this issue?? In the afternoon, the sun reflects off the panel into their kitchen window, bounces off the mirror and is extremely 'blinding'. Of course it only lasts for a few minutes, but they sound like they are ready to take us to court, which would probably cause us to move to somewhere with acreage where we can have panels and not neighbors. HELP!
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BiomimeticsRegistry.Net
4 Comments
Similar to Moth Eye Surfaces
Using nanostructures on surfaces to create anti-reflection and anti-glare is an approach that has long been used by night-flying moths. (See: http://www.engineeringtalk.com/news/aue/aue124.html ) For moths, every quanta of light carries information that may relate to its natural predators or may indicate a food source. It can't afford to lose this information so the nano surface features of their eyes insures that this light is not reflected away, but directed inward. What other optical engineering and material science inspirations might biological design paradigms provide?
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aaronm
1 Comment
Re: Similar to Moth Eye Surfaces
ummmm....right.....so when do we get to paint our cars with this stuff and bypass those pesky laser speed detectors?
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