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Posted: January 18, 2010

Nanoparticle coating can suppress light reflection on glasses

(Nanowerk News) Stuttgart physicists develop a new metallic coating. Whether eyewear or camera lenses: most optical components are anti-glare. Soon nanotechnology could be applied to the coating of optical glasses: Researchers of the University of Stuttgart’s 1st Physical Institute have come to know that coating with metallic nano particles can suppress light reflection almost entirely.
This allows for extremely thin coatings that could be of use particularly for integrated optics or solar cells. The renowned Physical Review B journal reports on this in its current issue ("Dielectric properties of ultrathin metal films around the percolation threshold").
A sufficiently thick metal film on a glass panel makes these opaque, as we can see in our bath room mirror each morning: all the light is being reflected. When this film is thinner than one one-thousandth millimeter, it becomes semi-transparent, which is used for spy mirrors for example.
However, if only few millionth millimeters of the metal are evaporated onto the glass, something unexpected happens: suddenly more light passes through the glass than without the metal. As Prof. Martin Dressel’s and Dr. Bruno Gompf’s research group has found out based on those pilot studys, the metal nano particles function as an anti-reflex-coating, whilst being a thousandth times thinner than with conventional methods.
Optical properties of ultra-thin metal coatings differ drastically from their volume characteristics. Films with a thickness of few nano meters are not united any longer, they constitute tiny islands. The so-called dielectric properties are characterized by an enormously large refraction index, right before a continuous metal film develops. This allows for producing structures with deliberately adjustable optical characteristics, which could be applied, for instance, in the future realization of photon integrated circuitries. This is what a team of physicists and engineers is working on within the new Stuttgart University’s Research Center for Photonic Engineering (SCoPE).
Source: University of Stuttgart
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