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Measuring the force to push a single atom deepens understanding of nanotechnology

By combining the features of a scanning tunneling microscope (STM) and an atomic force microscope (AFM)—two of the most useful nanotech tools—in a single instrument, IBM scientists have measured the forces necessary to move single cobalt atoms and single carbon monoxide molecules across metal surfaces. A better understanding of the forces involved in using scanning probes to manipulate atoms and molecules should allow a more systematic development of some types of nanotechnology. As described by Kenneth Chang in The New York Times in the article “Scientists Measure What It Takes to Push a Single Atom“:

I.B.M. scientists have measured the force needed to nudge one atom.

About one-130-millionth of an ounce of force pushes a cobalt atom across a smooth, flat piece of platinum.

Pushing the same atom along a copper surface is easier, just one-1,600-millionth of an ounce of force.

I.B.M. scientists have been pushing atoms around for some time, since Donald M. Eigler of the company’s Almaden Research Center in San Jose, Calif., spelled “IBM” using 35 xenon atoms in 1989. Since then, researchers at the company have continued to explore how they might be able to construct structures and electronic components out of individual atoms.

Knowing the precise forces required to move atoms “helps us to understand what is possible and what is not possible,” said Andreas J. Heinrich, a physicist at Almaden and an author of the new Science paper. “It’s a stepping stone for us, but it’s by no means the end goal.”

In the experiment, Dr. Heinrich and his collaborators at Almaden and the University of Regensburg in Germany used the sharp tip of an atomic force microscope to push a single atom. To measure the force, the tip was attached to a small tuning fork, the same kind that is found in a quartz wristwatch. In fact, in the first prototype, Franz J. Giessibl, a scientist at Regensburg who was a pioneer in the use of atomic force microscopes, bought an inexpensive watch and pulled out the quartz tuning fork for use in the experiment.

The tip vibrates 20,000 times a second until it comes into contact with an atom. As the tip pushes, the tuning fork bends, like a diving board, and the vibration frequency dips.

What this increased understanding of pushing atoms on metal surfaces will mean to using scanning probe microscopes to make and break covalent bonds as a path toward productive nanosytems can only be determined as further work is done. One would think it should be quite useful to be able to precisely measure forces of interacting with atoms and molecules. The researchers end their paper by saying “A systematic investigation of the manipulation forces on different surface-adsorbate combinations is now possible, and the driving mechanism to create future nanoscale devices can be explored in a quantitative manner.” The research was published in Science (abstract).
—Jim

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