To shrink circuits down, scientists are increasingly looking to ever tinier circuit elements, including single organic molecules. The weakest links when it comes to developing such molecular electronics are the often unstable connections between these molecules and their electrodes. These result from the size mismatch between the organic molecules and their far larger electrodes, as well as from the gold and sulfurous compounds often used to attach the molecules to the electrodes, which create only tenuous bonds, said researcher Colin Nuckolls, an organic chemist at Columbia University in New York.
Researcher Philip Kim, a physicist at Columbia University, with Nuckolls and their colleagues experimented with single-walled carbon tubes a nanometer or two in diameter, which are roughly the same width as the kind of molecules that inventors want to use in molecular electronics. They developed their hybrid devices by taking carbon nanotubes and cutting into them with highly ionized oxygen gas. This leaves molecule-sized gaps 10 or fewer nanometers wide in the nanotubes, whose ends are chemically receptive to robust amide linkages, the same kind found in proteins.
The scientists filled these gaps with conductive organic molecular bridges that formed robust links. "That's a much stabler interface than what's been done before," said chemist Mark Ratner at Northwestern University in Evanston, Ill. "This has the huge advantage of being air and water stable, while gold-sulfur interfaces, the ones that are almost always used when experimenting with molecular electronics, are not."
The researchers found they could essentially plug in organic molecules that created electronic devices that changed how well they conducted with alterations in the acidity or alkalinity levels. Nuckolls and his colleagues reported their findings in the Jan. 20 issue of the journal Science.
In the future, not only could such devices find use in computing, they could also serve as chemical sensors, said chemist Tim Swager at the Massachusetts Institute of Technology in Cambridge, Mass.
"There is technological promise for these devices in real-time diagnosis of disease and environmental monitoring," Nuckolls said. "There's nothing more sensitive than a single molecule sensor, because anything around that would affect it will perturb the current running through the device."
The researchers are currently in the process of partly automating device fabrication, "which will allow us to step up device yield and efficiency," Nuckolls added.
Charles Choi covers research and technology for UPI. E-mail: firstname.lastname@example.org