The soccer-ball-shaped carbon molecules called fullerenes continue to dazzle scientists, even though they have yet to make a splash in real-world products. Their unique properties, such as their spherical shape, have long intrigued materials researchers. Now, a pair of scientists based in France and Switzerland have discovered another odd fullerene property: They change the amount of electrical current they conduct when they are squeezed. The researchers have used this ability to build the world's smallest electrical amplifier.
The new device, which is reported in the current issue of Chemical Physics Letters, isn't likely to make its way into products anytime soon. But bottom-up engineering, say the researchers, could lead to ultrasmall microelectronic devices made up of just handfuls of molecules.
The European researchers--Christophe Joachim of the CNRS Laboratory for the Study of Materials and Structures in Toulouse, France, and James Gimzewski of IBM's Zurich Research Laboratory--essentially trapped a spherical 60-carbon fullerene, or buckyball, in a vise wired up to conduct electricity. They first isolated a buckyball on a metal surface with a scanning tunneling microscope (STM), which images the atomic contours of a surface by measuring changes in the electrical current that travels between the surface and an ultrasharp tip that scans across it. The researchers then pinned the buckyball between the STM tip and a metal surface, and measured how well electrons were able to travel, or tunnel, from the tip through the buckyball and to the metal.
When Joachim and Gimzewski moved the STM tip down, slightly flattening their buckyball, the molecule's electrical resistance dropped 100-fold, allowing the current to flow more easily from the STM tip to the metal surface. In their experimental setup, the researchers wired a pair of electrical circuits to use this effect to amplify an electrical signal fivefold.
The researchers don't expect to be able to use their buckyball amplifiers for practical applications anytime soon. Nevertheless, says Daniel Colbert, a physicist at Rice University in Houston, "nothing like this has been done before, and the experimental know-how to be able to do this is highly impressive." Moreover, says Colbert, such experiments could pave the way to the design of ultrasmall microelectronics devices on the scale of molecules. "The import is as a demonstration of things to come," says Colbert. "We are going to look back in 5 or 10 years and consider these things as important demonstrations of our beginning to play in this playground."