ROHRER, HEINRICH

born June 6, 1933, Switzerland Swiss physicist who, with Gerd Binnig, received half of the 1986 Nobel Prize for Physics for their joint invention of the scanning tunneling microscope. (Ernst Ruska received the other half of the prize.) Rohrer was educated at the Swiss Federal Institute of Technology in Zrich and received his Ph.D. there in 1960. In 1963 he joined the IBM Research Laboratory in Zrich, where he remained. Binnig also joined the laboratory, and it was there that the two men designed and built the first scanning tunneling microscope. This instrument is equipped with a tiny tungsten probe whose tip, only about one or two atoms wide, is brought to within five or ten atoms' distance of the surface of a conducting or semiconducting material. (An atom is equal to about one angstrom, or one ten-billionth of a metre.) When the electric potential of the tip is made to differ by a few volts from that of the surface, quantum mechanical effects cause a measurable electric current to cross the gap. The strength of this current is extremely sensitive to the distance between the probe and the surface, and as the probe's tip scans the surface, it can be kept a fixed distance away by raising and lowering it so as to hold the current constant. A record of the elevation of the probe is a topographical map of the surface under study, on which the contour intervals are so small that the individual atoms making up the surface are clearly recognizable.