7 Heinrich Rohrer and Gerd Binnig 7regions of space that are forbidden to them under the rules
of classical physics. The probability of finding such tunnel-
ing electrons decreases exponentially as the distance from
the surface increases. The STM makes use of this extreme
sensitivity to distance. The sharp tip of a tungsten needle
is positioned a few angstroms from the sample surface. A
small voltage is applied between the probe tip and the
surface, causing electrons to tunnel across the gap. As the
probe is scanned over the surface, it registers variations
in the tunneling current, and this information can be pro-
cessed to provide a topographical image of the surface.
Binnig and Rohrer chose the surface of gold for their
first image. When the image was displayed on the screen
of a television monitor, they saw rows of precisely spaced
atoms and observed broad terraces separated by steps one
atom in height. Binnig and Rohrer had discovered in the
STM a simple method for creating a direct image of the
atomic structure of surfaces. Their discovery opened a
new era for surface science, and their impressive achieve-
ment was recognized with the award of half the Nobel
Prize for Physics in 1986. (Ernst Ruska, a German electrical
engineer who invented the electron microscope, received
the other half of the prize.)
Heinrich Rohrer
Heinrich Rohrer was educated at the Swiss Federal
Institute of Technology in Zürich and received his Ph.D.
there in 1960. In 1963, after a period of postdoctoral work
at Rutgers University in New Jersey, he joined the IBM
Zürich Research Laboratory, where he remained until his
retirement in 1997. Binnig also joined the laboratory, and
it was there that the two men designed and built the first
STM. This instrument is equipped with a tiny tungsten
probe whose tip, only about one or two atoms wide, is