Scientists unveil one-step, flexible method to create nanoscale patterns

Washington, July 26 : University of Pennsylvania researchers claim to have devised a flexible method to produce functional nanoscale patterns or motifs that will have adjustable features, size, and shape.

They say that using a single master "plate" may make it possible in just one step.

The researchers have revealed that they take advantage of the elastic instability of a widely used, flexible polymer membrane called polydimethylsiloxane (PDMS).

According to them, 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.

When the researchers laced the solvent with iron nanoparticles, they found that evaporation of the solvent drives the assembly of the nanoparticles onto the membrane surface along the distorted pores.

They said that the process resulted in two-dimensional patterns with sub-100 nanometre features.

While the traditional fabrication process takes about a month and cost 50,000 dollars per print, the new process may help create a master for a fraction of the cost, and it can be reused many times.

Instead of having to depend upon delicate surface preparation or the complex chemistry of standard lithographic processes, the new process relies on patterns that form spontaneously in equilibrium.

The researchers say that the resulting, "diamond-plate" pattern persists over the entire sample, as large as a square centimetre, with no imperfections.

They also say that the features of the resultant nanoparticle patterns are up to 10 times sharper than the original membrane.

They insist that 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 School of Engineering and Applied Science at Penn, said.

"Using similar pattern transformation principles, our technique could be extended to pattern a variety of material systems such as polymers and composites, creating a new design mechanism for nanoscale manufacturing," Yang added.

For their study, the researchers modelled the elastic instability of the membrane in terms of elastically interacting "dislocation dipoles", and found complete agreement between the theoretical ground state and the observed pattern.

They said that the model allowed for the manipulation of the structural details of the membrane to tailor the elastic distortions, and generate a variety of nanostructures.

"It is both surprising and serendipitous that the simple theory is corroborated by experiment and by complex numerical simulations by other groups," Randall Kamien, professor in the Department of Physics and Astronomy in the School of Arts and Sciences at Penn, said.

The study has been published in the journal Nano Letters.

ANI