A CARBON NANOTUBE TRANSISTOR, an electronic device based on a single rolled-up sheet of carbon atoms, has been built by researchers in the Netherlands (Cees Dekker, Delft Institute of Technology, dekker@qt.tn.tudelft.nl), providing a demonstration of room-temperature, carbon-based electronics at the single-molecule scale. In the device, a semiconducting carbon nanotube (only about 1 nm in diameter) bridges two closely separated metal electrodes (400 nm apart) atop a silicon surface coated with silicon dioxide. Applying an electric field to the silicon (via a gate electrode) turns on and off the flow of current across the nanotube, by controlling the movement of charge carriers onto it. Although carbon nanotubes are robust and durable molecules, they can't yet be made uniformly. While this can provide disadvantages (a slight deviation from the desired radius can give the nanotube metallic properties), it can also bring about advantages--such as the possibility of a metal-semiconductor junction made completely of carbon nanotubes. (S.J. Tans et al., Nature, 7 May 1998; image at Physics News Graphics