Penn researchers demonstrate a flexible, 1-step assembly of nanoscale ...( PHILADELPHIA - Scientists at the Uni...)

PHILADELPHIA - Scientists at the University of Pennsylvania have created a one-step, repeatable method for the production of functional nanoscale patterns or motifs with adjustable features, size and shape using a single master "plate."

Researchers took advantage of the elastic instability of a widely used, flexible polymer membrane, polydimethylsiloxane, or PDMS. When exposed to a solvent, circular pores in the membrane elliptically deform, and elastic interactions between them generate long-range orientational order of their axes into a "diamond plate" pattern. By lacing the solvent with iron nanoparticles, the team found that evaporation of the solvent drives the assembly of the nanoparticles onto the membrane surface along these distorted pores.

This results in two-dimensional patterns with sub-100 nanometer features. The traditional fabrication process can take as long as a month and cost $50,000 per print. In this new process, a master can be made for a fraction of the cost and can be reused many times. The Penn team's technique does not require delicate surface preparation or the complex chemistry of standard lithographic processes. Instead, the new process relies on patterns that form spontaneously in equilibrium. The resulting, "diamond-plate" pattern persists over the entire sample, as large as a square centimeter, with no imperfections.

The features of the resultant nanoparticle patterns are up to 10 times sharper than the original membrane. The resulting symmetry of the film can be transferred onto a substrate, both flat or curved, where it can be used to generate similar anisotropic magnetic, photonic, phononic and plasmonic properties.

"These functional nano-motifs could in turn benefit novel technologies that are sensitive to local environment change such as smart clothing, biomarkers and eco-friendly buildings," Shu Yang, assistant professor in the Department of Materials Science and Engineering of the
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