in 1981. A principal problem for them was to prevent disturbances due to vibration; footfalls of people in the lab could resemble the San Francisco earthquake at atomic scale, while the vibrations of ordinary speech could resound like Big Ben tolling the hour. They succeeded, however, and at 2 a.m. one morning in mid-March, Binnig made his first observation with the new instrument. He had worked for weeks to overcome difficulties with a balky control system, but his reward came as he observed steps of atomic scale on a surface of gold. Later, observations of silicon showed bumps corresponding to single atoms, along with vertical resolutions, normal to the surface, as fine as 0.5 Å. Similar results have been seen in studies of nickel (see Figure 2.3).

The instrument that emerged from this work found quick application in making atomic-scale maps of surfaces. A common procedure involved a feedback control that would measure the tunneling current as the needle scanned over the surface, automatically adjusting the height of the needle to keep that current constant. The varying voltage fed to the vertical piezoelectric element, to adjust the needle height, then would correspond to the surface details seen while scanning. In the words of Binnig and Rohrer, "By sweeping the tip through a pattern of parallel lines a three-dimensional image of the surface is obtained. A distance of 10 centimeters on the image represents a distance of 10 Å on the surface: A magnification of 100 million." By contrast, a conventional optical microscope achieves a magnification of 2000, which is 50,000 times coarser.

"There they were, like tennis balls lying on the floor. Atoms!" recalls Calvin Quate of Stanford University, who in 1982 became one of the first American investigators to use this device. His excitement was understandable, for just after World War II the physicist Edward Teller had written an alphabet book for the nuclear age:

A is for atom. It is so small

No one has ever seen it at all.

The scanning tunneling microscope was not the first instrument to give direct views of individual atoms; using specialized techniques, physicists had seen tungsten atoms during the 1950s. But with this new microscope, physicists could see atoms at will, within a wide range of materials. Binnig and Rohrer went on to share the 1986 Nobel prize in physics for their achievement.



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