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Nanoporous anti-reflection coatings

Inkjet patterned anti-reflection coatings

Porous films are important in many applications ranging from optics to filtration to biomaterials. In optics, nanoporous films are used to eliminate unwanted surface reflections due to the fact that, being filled with air, they have a lower refractive index than typical optical substrates. Nanopores, in turn, are needed to prevent light scattering from the pores. Within the MIT MRSEC,1 we have discovered a very simple, low cost method for making porous thin films with pore sizes controllable from the micro- to nanometer scale. The nanoporous films can also be reversibly converted from a porous to nonporous state by simple water treatments making them useful for drug delivery and pH-controlled filtration applications. The nanoporous films can also be "locked-in" permanently and used as a low cost anti-reflection coating for plastics and glass.

The image below shows a glass slide that was patterned with an ink-jet printer (using water as the ink) to create regions coated with the nanoporous film (no reflection of light) and regions not coated (strong gold reflecting regions). The coated regions transmit more light (at some wavelengths close to 100%) than the uncoated regions. Optical grade glass and plastics typically reflect about 8% of incident light resulting in poor image quality in displays and low efficiencies in solar cells, for example. The ease of producing these nanoporous coatings using only water-based processing makes them ideal teaching vehicles for basic principles of chemistry and physics. MRSEC supported graduate student Jeri-Ann Hiller and RET participant Steve Rhule (Delaware Valley High School) have developed laboratory modules for high school students. Modules based on these materials have also been introduced into undergraduate labs at MIT.

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