The smaller components become, the more difficult it is to create patterns in an economical and reproducible way, according to an interdisciplinary team of Penn State researchers who, using sound waves, can place nanowires in repeatable patterns for potential use in a variety of sensors, optoelectronics and nanoscale circuits.
"There are ways to create these devices with lithography, but it is very hard to create patterns below 50 nanometers using lithography," said Tony Jun Huang, associate professor of engineering science and mechanics, Penn State. "It is rather simple now to make metal nanomaterials using synthetic chemistry. Our process allows pattern transfer of arrays of these nanomaterials onto substrates that might not be compatible with conventional lithography. For example, we could make networks of wires and then pattern them to arrays of living cells."
The researchers 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.
In this case, the researchers applied an alternating current to the substrate so that the material's movement creates a standing surface acoustic wave in the solution. A standing wave has node locations that do not move, so the nanowires arrive at these nodes and remain there.
If the researchers apply only one current, then the nanowires 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 forms and the nanowires move to those grid-point nodes and form a three-dimensional spark-like pattern.
"Because the pitch of both the one-dimensional and two-dimensional structures is sensitive to the frequency of the standing surface acoustic wave field, this technique allows for the patterning of nanowires with tunable spacing and density," the researchers report in a recent issue of ACS Nano.
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