Microspheres simplify nanopatterning processes

Commercially available microspheres are being used in numerous applications—from creating white-light sources by coating red and green fluorescent microspheres on blue light-emitting diodes.

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Commercially available microspheres are being used in numerous applications—from creating white-light sources by coating red and green fluorescent microspheres on blue light-emitting diodes (see www.laserfocusworld.com/articles/318539), to acting as dyed biomaterials in laser-removable tattoo inks (see www.laserfocusworld.com/articles/255480). Now, researchers at Northwestern University (Evanston, IL) have extended the range of uses for microspheres by applying them in a self-assembling array for maskless nanopatterning. Basically, microspheres of varying size and material composition are flowed in solution and uniformly self-assemble over the substrate to be patterned. This planar array of spheres acts as a set of tiny lenses to focus light onto the substrate and create the desired pattern—either nanoholes (for negative photoresist substrates) or nanopillars (for positive photoresist substrates).

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Similar work is being performed at Johannes Kepler University (Linz, Austria), but the Northwestern team says it does not use an expensive ultraviolet (UV) laser as the source in a relatively slow rastering mode, but instead can use any broadband UV source in a single-shot, high-throughput exposure to create the desired holes or pillars. Such patterned nanostructures are finding use in solar cells, nanofiltration systems, and fuel cells. Contact Hooman Mohseni at hmohseni@northwestern.edu

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