Sound Waves Precisely Position Nanowires: The Future of Tiny Technology

Technology is getting smaller and smaller. Televisions are becoming flatter, batteries becoming miniscule and devices are getting more and more upgrades. Yet the smaller components become, the more difficult it is to create patterns in an economical and reproducible way. Now, though, scientists have developed a new technique that involves using sound waves to place nanowires in repeatable patterns for potential use in a variety of nanoscale circuits.

There are actually ways to create these devices with lithography, a type of printing. Yet it's extremely difficult to use this technique to create patterns that are smaller than 50 nanometers. In contrast, it's relatively simple to make metal nanomaterials using synthetic chemistry. With the new technique, scientists could transfer arrays of nanomaterials onto substrates that might not be compatible with conventional lithography.

In order to develop this new technique, scientists looked at the placement of metallic nanowires in solution on a piezoelectric substrate. Piezoelectric materials move when an electric voltage is applied to them and create an electric voltage when compressed. The researchers then applied an alternating current to the substrate so that the material's movement created a standing surface acoustic wave in the solution. This standing wave had node locations that do not move, so that the nanowires arrive at these nodes and then remain there.

The technique itself involves applying only one current, causing the nanowires to form a one-dimensional array with the nanowires lined up head to tail in parallel rows. If perpendicular currents are used, a two-dimensional grid of standing waves form and the nanowires move to those grid-point nodes to form a three-dimensional spark-like pattern. The nanowires in the solution will eventually settle in place onto the substrate when the solution evaporates, preserving the pattern.

"We really think our technique can be extremely powerful," said Tony Jun Huang, associate professor of engineering science and mechanics at Penn State, in a news release. "We can tune the pattern to the configuration we want and then transfer the nanowires using a polymer stamp."

The findings could allow scientists to save a lot of time when compared to lithography. In addition, the technique could be used to create a variety of sensors and optoelectronics.