Image: Courtesy of CEES DEKKER and HENK POSTMA, Delft University of Technology
From a carbon nanotube, Dutch researchers have crafted a transistor that toggles on and off with the flow of a single electron. It is the first such single-electron transistor (SET) to operate at room temperature, and given its efficiency and size, the scientists suggest it represents a big step forward in the quest to create ever-smaller computer components. "We've added yet another important piece to the toolbox for molecular electronics," Cees Dekker of Delft University of Technology says. Dekker and his colleagues publish their work in today's issue of Science.
Ordinary transistors rely on the motion of millions of electrons, which, when pressed close together, generate a great deal of heat. As a result, scientists can shrink these designs only so far. A single electron switch makes it possible to sidestep the size barrier. These devices consist of a metallic island separated from two electrodes by a surrounding "sea" of material. Voltage applied to a gate on the island makes it possible for electrons to tunnel through the sea and hop on or off the island. But heat, too, it turned out, could supply the electrons with enough energy to island hop.
Dekker's group skirted the issue by making their SET so tiny¿one nanometer wide and 20 nanometers long¿that heat fluctuations proved irrelevant. They used the tip of an atomic force microscope to put sharp bends in a single carbon nanotube (see image). These bends served the same purpose as the sea material in the earlier devices, regulating the number of electrons passing through the SET. "Only four years ago did we measure for the first time any electronic transport through a nanotube," Dekker notes. "Now we are exploring what can be done and what cannot in terms of single-molecule devices. The next step will be to think about how to combine these elements into complex circuits."