Number 45 (Story #1), August 30, 1991 by Phillip F. Schewe and Ben Stein AN ATOMIC SWITCH , whose "on" and "off" state depends on the position of a single atom, has been devised by researchers at IBM Almaden Research Center (contact: Don Eigler, 408-927-2172). Using STM technology, the IBM scientists have been able to manipulate a single xenon atom reversibly to and from nickel substrates. Voltage pulses change the position of the atom and designate the state of the switch, which can be determined by measuring the conductance between the tip and surface: if the xenon atom is on the substrate surface, the conductance is low and the switch if "off"; if the atom is instead drawn to the tip, the conductance is high and the switch is "on." This achievement may facilitate the design of electronic devices of atomic dimensions. Although the reading and writing of data to such devices would be painfully slow with present methods, the entire contents of the Library of Congress---estimated to take up the equivalent of 250,000 compact disks---would fit on a single twelve-inch disk composed of atom switches. (Nature, 15 August, 1991.)