A well-known axiom of technology states that every 18 to 24 months, advancements produce computers that process information twice as quickly as their speediest predecessors. At some point, however, limiting factors such as space on a silicon chip and heat generated by intense electrical activity will prevent further computational acceleration. Luckily, researchers working in the field of nanotechnology have been investigating another way to transmit information through the hardware of a computer: atoms. If these fundamental building blocks could themselves act as transistors to control the flow of electricity, many more circuits could be integrated on a silicon chip, resulting in exponential increases in computing speed. To that end, findings published by two different teams today in the journal Nature show that creating such single-molecule transistors is indeed possible.
Silicon chips laced with thousands of electrical circuits comprise the inner workings of a traditional computer. Each circuit contains transistors, which allow electrons, or current, to either pass through ("on") or remain where they are ("off"). Like tiny switches, these electron gates form the basis of a computer¿s ability to store information and perform calculations. Scientists must be able to turn them on and off at will, as well as amplify the current. In the new work, researchers at Cornell University and Harvard University massaged a similar function out of a single cobalt atom in one case and two vanadium atoms in the other. An incredibly difficult feat, constructing these circuits required the fabrication of "designer molecules" composed of various scaffolding particles that support the central cobalt or vanadium atoms. Utilizing such inherent physical properties of electrons as spin and aversion to other electrons, the investigators applied a small amount of energy to the circuit and were able to sustain a one-electron current through the central molecule, as well as turn it on and off.
Although the new research represents an important first step, practical applications for molecular transistors remain a long way off. Amplification of electrical current is still not feasible, and difficulties associated with creating single-molecule circuits currently restrict usage. But scientists are optimistic. "Right now, these single-molecule or single-atom transistors are no competition for silicon transistors," Silvano De Franceschi and Leo Kouwenhoven remark in an accompanying commentary. "But they will serve for studying electron motion through nanoscale objects, and for the development of integrated electronic devices built on single molecules."