Rice University’s coaxial nanocable outperforms previous microcapacitors
Thanks to a little serendipity, researchers at Rice University have created a tiny coaxial cable that is about a thousand times smaller than a human hair and has higher capacitance than previously reported microcapacitors.
The nanocable was produced with techniques pioneered in the nascent graphene research field and could be used to build next-generation energy-storage systems. It could also find use in wiring up components of lab-on-a-chip processors, but its discovery is owed partly to chance.
“We didn’t expect to create this when we started,” said study co-author Jun Lou, associate professor of mechanical engineering and materials science at Rice. “At the outset, we were just curious to see what would happen electrically and mechanically if we took small copper wires known as interconnects and covered them with a thin layer of carbon.”
The tiny coaxial cable is remarkably similar in makeup to the ones that carry cable television signals into millions of homes and offices. The heart of the cable is a solid copper wire that is surrounded by a thin sheath of insulating copper oxide. A third layer, another conductor, surrounds that. In the case of TV cables, the third layer is copper again, but in the nanocable it is a thin layer of carbon measuring just a few atoms thick. The coax nanocable is about 100 nanometers, or 100 billionths of a meter, wide.
While the coaxial cable is a mainstay of broadband telecommunications, the three-layer, metal-insulator-metal structure can also be used to build energy-storage devices called capacitors.
The study reports that the capacitance of the nanocable is at least 10 times greater than what would be predicted with classical electrostatics. The capacitance of the new nanocable is up to 143 microfarads per centimeter squared, better than the best previous results from microcapacitors.
It may be possible to build a large-scale energy-storage device by arranging millions of the tiny nanocables side by side in large arrays.
The nanoscale cable might also be used as a transmission line for radio frequency signals at the nanoscale. This could be useful as a fundamental building block in micro- and nano-sized electromechanical systems like lab-on-a-chip devices.
