In the drive to miniaturize electronics, solenoids have become way too big, say Rice University scientists who discovered the essential component can be scaled down to nano-size with macro-scale performance.
The secret is in a spiral form of atom-thin graphene that, remarkably, can be found in nature, according to Rice theoretical physicist Boris Yakobson and his colleagues.
“Usually, we determine the characteristics for materials we think might be possible to make, but this time we’re looking at a configuration that already exists,” Yakobson said. “These spirals, or screw dislocations, form naturally in graphite during its growth, even in common coal.”
The researchers determined that when a voltage is applied, current will flow around the helical path and produce a magnetic field, as it does in macro inductor-solenoids. The discovery is detailed in a new paper in the American Chemical Society journal Nano Letters.
“One can compare the structure to a high-rise parking lot for electrons—but without parking spaces, so the electrons just drive through,” Yakobson said. “Or you can say it resembles Archimedes’ screw—which rotates in order to pump water uphill—but filled with electricity instead.
“Perhaps this might work in reverse here: An electron current, pumped through by the applied voltage, at certain conditions may just cause the graphene spiral to spin, like a fast little electro-turbine,” he said.
Solenoids are wires coiled around a metallic core. They produce a magnetic field when carrying current, turning them into electromagnets. These are widespread in electronic and mechanical devices, from circuit boards to transformers to cars. They also serve as inductors, primary components in electric circuits that regulate current, and in their smallest form are part of integrated circuits. (The lump in power cables that feed electronic devices contains inductors.)
While transistors get steadily smaller, basic inductors in electronics have become relatively bulky, said Fangbo Xu, a Rice alumnus and lead author of the paper. “It’s the same inside the circuits,” he said. “Commercial spiral inductors on silicon occupy excessive area. If realized, graphene nano-solenoids could change that.”