Rohrer, Heinrich

views updated May 23 2018

Heinrich Rohrer

Swiss physicist Heinrich Rohrer (born 1933) received a share of the 1986 Nobel Prize in Physics for his part in inventing, with Gerd Binning, the scanning tunneling microscope, an instrument so sensitive that it distinguishes individual atoms. Rohrer spent most of his career at the IBM Research Laboratories in Switzerland, where he conducted his most significant research. His other research interests included superconductivity, multicritical phenomena, and nanotechnology.

Rohrer was born in Buchs, Switzerland, on June 6, 1933, to Hans Heinrich Roher and Katharina (Ganpenbein) Rohrer. His father was a distributor of manufactured goods. Rohrer was one of the family's three children, and was born a half-hour after his twin sister. He recalled his childhood as being relatively care free, with play, farm work, and schooling occupying much of his time. In 1939, when he was 13 years old, Rohrer's family moved from the country to the large city of Zurich, a move that changed their lifestyle.

As a student, Rohrer was interested in physics, chemistry, and classical languages. He decided to concentrate on physics when he enrolled at the Swiss Federal Institute of Technology in Zurich in the autumn of 1951. One of his professors was Wolfgang Pauli, who won the Nobel Prize in Physics in 1945 for the discovery of the exclusion principle, better known as the Pauli principle. From Pauli and his other professors, Rorher learned the fundamentals of physics, and he received a bachelor of science degree from the Institute in 1955.

Conducted Graduate Work on Superconductors

In the autumn of 1955, Rohrer started work on his Ph.D. thesis on superconductivity. "It was fortuitous that Jörgen Lykke Olsen trusted me to measure the length changes of superconductors at the magnetic field-induced superconducting transition," Rohrer said in his autobiography posted on the Nobel Prize Website. "He had already pioneered the field with measurements on the discontinuity of Young's modulus. Following in his footsteps, I lost all respect for angstroms [an atomic measure]. The mechanical transducers were very vibration sensitive, and I learned to work after midnight, when the town was asleep." Rohrer recalled that his graduate years were fun and memorable, although they were interrupted by his basic training in the Swiss mountain infantry. He received his Ph.D. in experimental physics from the Institute in 1960, and for a year afterward worked as a research assistant at the institute.

In the summer of 1961, Rohrer married Rose-Marie Egger, whom he has credited with bringing a stabilizing influence into his life. The couple took their honeymoon in the United States, where Rohrer spent two years doing postdoctorate research at Rutgers University in New Brunswick, New Jersey, working on the thermal conductivity of type-II superconductors and metals.

Joined IBM in Switzerland

Following a four-month camping trip through the United States, Rohrer returned to Switzerland in 1963. In the summer of that year, Ambros Speiser, director of the newly founded IBM Research Laboratory in Ruschlikon, Switzerland, offered Rohrer a position at the company as a research staff assistant. Encouraged to accept this position by his professor Bruno Luthi, Rohrer joined IBM in December of 1963. His research efforts interests included Kondo systems, phase transitions, multicritical phenomena, scanning tunneling microscopy and, most recently, nanomechanics.

By the end of the decade, colleague Keith Blazey, who had done optic experiments on GdAlO3, an antiferromagnet, asked Rohrer to work with him. Thus began the collaboration on magnetic phase diagrams that would eventually lead Rohrer into the field of critical phenomena. K. Alex Muller, who won a share of the 1987 Nobel Prize in Physics for breakthroughs in the discovery of superconductivity in ceramic materials, had pioneered efforts in critical phenomena at IBM's Ruschlikon laboratory, and he encouraged Rohrer in this new direction. Roher focused on the bicritical and tetracritical behavior and on the random-field problem. "These were most enjoyable years, during which so many patient colleagues taught me physics," recalled Rohrer in his Nobel autobiography.

Rohrer remained involved with IBM throughout his career. "In all the years with IBM Research, I have especially appreciated the freedom to pursue the activities I found interesting, and greatly enjoyed the stimulus, collegial cooperation, frankness, and intellectual generosity of two scientific communities, namely, in superconductivity and critical phenomena," Rohrer wrote in his Nobel autobiography. Until he retired, Rohrer's only time away from the company came in the mid-1970s, when he took a year-long sabbatical to study nuclear magnetic resonance at the University of California, Santa Barbara. Curious about nuclear magnetic resonance, Rohrer began the sabbatical in 1974, working with professors Vince Jaccarino and Alan King. Together the three men solved a specific problem on the bicritical point of MnF2, their home-base material.

By this time, Rohrer and his wife had two daughters, Doris and Ellen, and they used the sabbatical opportunity to show their children the United States on two extended camping trips, one that preceded and one that followed the research at the university.

Began Collaboration with Binnig

Rohrer eventually became interested in the complex atomic structures of surface materials, structures that were then little understood. The development of the electron microscope had enabled investigation into the arrangements of atoms in materials, but attempts to discover information about the much different nature of surface atoms had met with little success.

In 1978 in Zurich, Rohrer began a fruitful collaboration with Gerd Binnig, a young German who had just completed his doctorate work. Rohrer and Binnig began exploring oxide layers on metal surfaces. To further their research, they decided to develop a spectroscopic probe. However, in the process, they designed a new type of microscope, one that would make it possible to study, in the greatest detail possible, the atomic structure of the surface being examined. Images of individual atoms on a metal or semiconductor surface would be formed by scanning the tip of a needle probe over the surface, at a height of only a few atomic diameters.

Development of this unique microscope began when Rohrer and Binnig used a technique called tunneling. Quantum mechanics had revealed that electrons behave in a wave-like fashion that causes them to create a spreading cloud as they are emitted from the surface of a sample. When the electron clouds from two close surfaces overlap, the electrons then "tunnel" from one cloud to the other. The technique of causing such tunneling through an insulating layer had been useful in revealing information about the atomic materials on either side of the insulation.

For their approach, Rohrer and Binnig tunneled through a vacuum and then used a needle-like probe inside the vacuum to scan the sample surface. As the tip of the probe neared the sample, the electron clouds of each overlapped and a tunneling current began to flow. The scientists employed a feedback mechanism that harnessed the current to keep the probe tip at a constant height above the sample surface, enabling the tip to follow the contours of the individual atoms of the scanned surface. A computer then processed the tip's motion and used the data to produce a three-dimensional, high-resolution image of that surface.

From the start, Rohrer and Binnig knew they were on to something with this innovative technique. However, they encountered problems, the first being that the probe tip was sensitive to disturbances from vibration and noise. Building upon Rohrer's previous experience with superconductors, where transducers experienced the same kind of sensitivity, Rohrer and Binnig decided to shield the probe from disturbances with magnets and a heavy stone table set on inflated rubber tires. This solved their problem. The basic device was successfully tested in 1981, and Rohrer and Binnig then refined it technologically. The resulting microscope was built on a heavy permanent magnet floating in a dish of superconducting lead. By the mid-1980s, all but the vacuum chamber of the scanning tunneling microscope could fit in the palm of one's hand and could show details as tiny as one-tenth of an angstrom. One angstrom is equivalent to the diameter of a single atom, or 2.5 billionths of an inch.

Later, scanning tunneling microscopes were developed that would also work in water, air, and cryogenic fluids. In 1987, Rohrer's research group at IBM had developed a scanning tunneling microscope the size of a fingertip.

Won Nobel Prize

In 1986, Rohrer and Binnig received the Nobel Prize in Physics for inventing the scanning tunneling microscope. They shared the award with Ernst Ruska, who was recognized for his fundamental work in electron optics and for designing the first electron microscope. When awarding the Nobel Prize, the Royal Swedish Academy of Sciences said that the scanning tunneling microscope was a completely new device that was only at the beginning of its development. While acknowledging that the device had only been successfully tested for the first time in 1981, the Academy added: "It is, however, clear that entirely new fields are opening up for the study of the structure of matter. Binnig's and Rohrer's great achievement is that, starting from earlier work and ideas, they have succeeded in mastering the enormous experimental difficulties involved in building an instrument of the precision and stability required."

As the Swedish Academy expected, the scanning tunneling miscroscope was soon used in fields as diverse as semiconductor science, metallurgy, electrochemistry, and molecular biology. More recently, it has proved to be an essential tool for the new science of nanotechnology.

Later Career

Besides their Nobel prize, Rohrer and Binnig also received the King Faisal Prize and the Hewlett Packard Europhysics Prize in 1984 for their invention of the scanning tunneling microscope. In 1987, Rohrer received the Cresson Medal of the Franklin Institute in Philadelphia. The invention of the miscroscope also led to Rohrer's induction into the U.S. National Inventors Hall of Fame in 1994. In addition, Rohrer has also been awarded honorary doctorates by several universities.

Continuing his work following the Nobel award, Rohrer was appointed an IBM fellow in 1986, and he served as manager of the physical sciences department at the Zurich Research Laboratory from 1986 to 1988. He retired from IBM in July of 1997 and accepted research appointments at the Consejo Superior de Investigaciones Científicas in Madrid, Spain, and at Riken and Tohoku University in Japan.

The Small World of Nanoscience

In more recent years, Rohrer's interest has focused on nanoscience and nanotechnology. Nanoscience involves particles that are smaller than atoms. A nanometer is one-billionth of a meter, or 1/1,000,000,000th of a meter. Five hydrogen atoms placed side by side would span about one nanometer. A single human cell encompasses thousands of nanometers.

At this level, scale is so small that generally accepted principles of physics no longer apply. Forces such as inertia, friction, and gravity act differently or are not even meaningful. Nanoscience tries to make sense of how matter behaves at this level, while nanotechnology involves research and technology development at the atomic, molecular or macromolecular levels; creating and using the structures, devices, and systems that have the properties needed to deal with such material; and the ability to control or manipulate on the atomic scale.

Rohrer believes the world should be ready to exploit the new possibilities nanotechnology represents. In addition, he feels that devices like the scanning tunneling microscope would be useful in addressing one of the biggest challenges of nanoscience and nanotechnology: improving the interface between the macroscopic world of traditional manufacturing and the "nano" world. The scanning tunneling microscope could help create such an interface and thus become one of the major tools of nanotechnology. Along with its imaging capabilities, the microscope could be reconfigured to manipulate molecules and atoms, and it would enable researchers and product developers to observe what happens at the molecular level, so that they could modify and manufacture items at the nano level.