Room-temperature electron ratchets Conventional diodes rectify current flow by forming a junction between dissimilar conductors; a metal-semiconductor diode that forms a Schottky barrier is one example. In these devices, capacitance limits operating frequency. Custer et al. describe a diode made entirely of silicon that can rectify currents up to 40 gigahertz at room temperature. They fabricated silicon nanowires with a cylindrical sawtooth profile that act as ratchets, funneling current preferentially in one direction through specular reflection of quasi-ballistic electrons. Science , this issue p. 177