HOLOGRAMS OF TRANSISTOR INTERIORS can provide maps of electrostatic potentials in that crucial zone beneath the transistor's gate, where the passage of electrons from emitter to drain can be made difficult or easy, just as a water tap can switch a faucet on and off. Why are such maps necessary? "Within a decade, integrated circuits will consist of transistors 150 atoms long and 50 atoms deep," according to researchers at the Institute for Semiconductor Physics in Frankfurt (Oder), Germany, and knowledge of the precise whereabouts of dopant atoms will be vital. To this end, the Frankfurt scientists (Wolf-Dieter Rau, rau@ihp-ffo.de, 011-49-335-562-5432) can now produce a subsurface sectional map of the transistor. Electron waves from a transmission electron microscope (in which the quantum wavelike properties of electrons are more important than their particle properties) pass through the thin transistor, where they scatter slightly. These waves are recombined with some unscattered electron waves to form a holographic signal which encodes information about local conditions throughout the section. The electron data can be processed into 2-dimensional images with 10-nm resolution and high sensitivity. (Rau et al., Physical Review Letters, 22 March; see figure at Physics News Graphics)