Number 85 (Story #3), June 19, 1992 by Phillip F. Schewe and Ben Stein SINGLE-ELECTRON DEVICES , nanoscale devices that control the movement of individual electrons, may one day make it possible for integrated circuits to have as many as 10 billion electronic devices in a square centimeter, a density 1000 times greater than that believed feasible for conventional integrated circuits. In development since the mid-1980s, these devices consist of two electrodes (typically 30 nm wide) separated by a 1 nm-deep insulating layer through which single electrons can tunnel. These devices have many potential applications, from building more sensitive measurement devices to understanding fundamental problems in physics. In the last several years, researchers have built two-junction devices that share a middle electrode. These devices are called "single-electron transistors," because, like conventional transistors, their current can be controlled by modifying the surface charge on the middle electrode, making it an ideal element for an integrated circuit. A circuit made of single-electron devices, however, would have to be operated at a temperature of 4 K or below to reduce thermal effects which disturb the movements of single electrons in the solid. (Scientific American, June 1992.)