No Small Feat : Atom Research Could Widen Horizon of Miniaturization

IBM researchers in San Jose have succeeded in moving single atoms around under a microscope, a major step toward the fabrication of atom-sized transistors, exceptionally small integrated circuits and even molecule-sized mechanical devices.

Among other things, these ultraminiaturized electronic components could allow researchers to build microcomputers that operate hundreds to thousands of times faster than the fastest supercomputers available today and that store data at densities almost undreamed of now.

The technique should also provide new understanding of the so-called surface catalysts that are used in making as much as 85% of the products of the petrochemical industry.

The researchers report in today’s Nature that they manipulated the atoms using an expensive, custom-built scanning tunneling microscope, which is so sensitive that it must be shielded from body heat and the voices of people in the same room.

Their prize specimen: 35 xenon atoms painstakingly arranged over a 22-hour period to spell out “IBM” in letters that are one five-hundred-thousandth the size of letters on this page.

But physicists Donald M. Eigler and Erhard K. Schweizer of IBM’s Almaden Research Center in San Jose foresee far more practical applications for their technique. They noted that it should be possible to modify or assemble certain molecules by the technique, especially molecules that are otherwise unobtainable.

Manufacturers of synthetic rubber, for example, might be able to use catalysts composed of clusters of two or three metal atoms to produce highly specialized materials. Such clusters are very difficult to produce by chemical reactions, but might be made easily with the new technique.

Physicist Sheldon Schultz of UC San Diego called the work “a real contribution.” The IBM researchers, he said, have “demonstrated the ability to place atoms with atomic precision. It’s the first time it has been done anywhere near that level. . . . You can’t have any more control than that. It is the ultimate resolution.”

The scanning tunneling microscope was invented in the early 1980s by physicists Gerd Binnig and Heinrich Rohrer of IBM’s Zurich Research Laboratory in Switzerland, a feat for which they won the 1986 Nobel Prize for physics.

The device works in a manner similar to a phonograph. An extremely small needle, whose tip is formed by a single atom, passes over the surface of an object in a regular pattern. A principle of physics called the tunneling effect keeps the tip of the needle a precise distance from the surface.

As the tip moves up and down to follow the contours of the object, sensitive electronics measure its motion and convert that information into a detailed picture of the surface. The microscope can “see” objects as small as a single atom.

But Eigler and Schweizer, who was a visiting scientist from the Fritz Haber Institut in West Germany when the work was done in November of last year, found that by placing the tip closer to a surface atom than normal, they could drag the atom along with the tip as they moved it.

Eigler said in a telephone interview that he believes that electrostatic attraction caused the atom to follow the tip until electrical current through the tip is reduced, but that they are doing further studies to show precisely how the phenomenon occurs.

“We’ve made educated guesses about what the mechanism was,” he said. “Now, we are trying to go beyond guesses to the point of hard science.”

For their experiments, Eigler and Schweizer used a highly purified nickel surface cooled to a temperature of minus 452 degrees Fahrenheit, about seven degrees above absolute zero, and kept under an ultra-high vacuum. The system is so stable, they said, that they can perform experiments on a single atom for days at a time.

To write out IBM, Eigler said, he allowed a few dozen atoms of xenon--a heavy, inert gas--to condense onto the surface, then meticulously moved them around with the microscope tip. The feat took him “22 hours nonstop,” he said, “because we would sometimes destroy or partially destroy it (the design) through not being careful.”

Now, he said, they have overcome those problems and can do it in “a couple of hours.”

The researchers also built a small structure consisting of seven atoms of xenon weakly bound together in a row. Eigler said he realized the atoms were bonded together when he found he could relocate up to three of them at a time by moving an end atom.