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Heinrich Rohrer

Swiss physicist Heinrich Rohrer co-invented the scanning tunneling microscope (STM), a non-optical instrument that allows the observation of individual atoms in three dimensions, with Gerd Binnig.

Heinrich Rohrer

The achievement garnered the pair half of the Nobel Prize in Physics in 1986. The Royal Swedish Academy of Sciences bestowed the other half of the prestigious award to Ernst Ruska for the invention of the electron microscope. The fact that the STM was a mere five years old when Binnig and Rohrer won the Nobel Prize (Ruska had invented his device back in the 1930s) is testament to the groundbreaking nature of the invention and the scientific community’s understanding of its tremendous import.

Rohrer was born to Hans Heinrich Rohrer and Katharina Ganpenbein Rohrer on June 6, 1933. A native of Buchs, Switzerland, he spent his earliest years in the country, but moved with his family to Zürich as a teenager. In 1951, he began coursework at the Swiss Federal Institute of Technology (ETH), where he majored in physics and had the opportunity to learn from such prominent scientists as Wolfgang Pauli and Paul Scherrer. Rohrer obtained a B.S. in 1955, followed by a Ph.D. in 1960. He then accepted a research assistantship at the ETH, but left for the United States in 1961 to do postdoctoral research on superconductivity at Rutgers University in New Jersey. The trip was also a chance to honeymoon with his new bride, Rose-Marie Eggar, with whom he would have two daughters.

In 1963, Rohrer returned to his homeland and began working at the IBM Research Laboratory. There his interests expanded to include antiferromagnetism, critical phenomena, nuclear magnetic resonance and surface physics. His focus on surface physics eventually led him to develop the scanning tunneling microscope with Gerd Binnig, a young scientist hired by IBM in 1978. While investigating surface imperfections of layers of oxide deposited on metals, the pair found no suitable instrument to make the kind of observations they desired. The electron microscope invented by Ruska allowed study of atomic organization within samples, but not the individual surface atoms Rohrer and Binnig were interested in. So the IBM researchers decided to build the device they needed themselves.

At first, Rohrer and Binnig planned to construct a spectroscopic probe, but the project grew into something much more phenomenal — the scanning tunneling microscope. The STM is based on a quantum mechanical phenomenon known as electron tunneling. The properties of electrons cause them to spread out in clouds when they are emitted from the surface of a material, and when two surfaces are placed very close to one another, their clouds of electrons tend to overlap. Electrons in overlapping clouds are able to “tunnel” back and forth.

In the STM, a very fine-tipped probe slowly scans the surface of a sample, allowing electrons to tunnel between the probe tip and the surface. This creates a measurable current. A feedback mechanism makes adjustments in the height at which the probe tip is maintained so that the current is held at a constant level, as is the distance between the probe tip and sample surface. All vertical variations are recorded, and then a computer uses this information to produce a three-dimensional depiction of the surface on an atomic scale.

About two years after they had begun their work on the STM, Rohrer and Binnig were ready to announce their invention. A 1981 in-house report at IBM contained the first published discussion of the microscope. The pair continued to fine-tune the device, so better results could be obtained. His role in the invention of the STM garnered Rohrer, in addition to the Nobel Prize, the German Physics Prize, the Otto Klung Prize, the Hewlett Packard Europhysics Prize, the King Faisal Prize, the Cresson Medal and induction into the U.S. National Inventors Hall of Fame.

Over the course of his career, Rohrer advanced steadily at IBM. He took a year-long hiatus in the mid-1970s to travel to the University of California, Santa Barbara, as a visiting scholar. IBM eventually promoted Rohrer to head of the lab’s physics department and appointed him an IBM Fellow. Following his retirement in 1997, Rohrer has continued to carry out scientific investigations, accepting various research appointments around the world. Much of his later work has centered on nanotechnology, a field he was key in opening up with the invention of the STM.