Pushing and Shoving Single Atoms

If scientists could easily manipulate single atoms, they might one day be able to build drugs and other molecules with unprecedented precision. It might even be possible to design computer disk drives that store vast amounts of data by moving atoms one by one. Now scientists have heated up the race for this technology by pushing a single bromine atom across a copper surface at room temperature. Until now, the technique was prohibitively expensive because it had to be performed near absolute zero.

It's not hard to see single atoms with a scanning tunneling microscope (STM). But as quantum physicists and bird watchers know, you can't look too closely without being a disturbance; the small electric current between the tip of the STM probe and the sample surface can dislodge weakly bound atoms, freeing them to bounce away. "The atoms become like sticky fuzzy balls," says physicist John Pethica of the University of Oxford, United Kingdom. This has allowed researchers to rearrange individual atoms on a sample.

There's a catch: The entire system must be kept near absolute zero to prevent atoms from jiggling off the surface, like popcorn popping out of an uncovered pan. A decade ago, physicist Don Eigler, an IBM Fellow in San Jose, California, successfully moved a single weakly bound atom of hydrogen along a supercooled silicon surface, but progress since then has been slow because these cryogenic STMs are rare and expensive.

In the 13 April Nature, Pethica and his group report success at pushing their tiny atomic marbles at room temperature. The key was to use bromine atoms, which are held fast to a copper surface by strong chemical bonds. By placing the STM tip very near a protruding atom, Pethica's team induced a small electric current that heats the bromine atom, temporarily breaking the copper-bromine bond and allowing the atom to skip to the next space on the egg-box shaped copper surface. "We can herd it from one site to the next," Pethica says.

Being able to do these experiments at room temperature is a tremendous advance, says Eigler. "It will accelerate the pace of work in this field dramatically." And that is important, because ultrahigh-density computer disks and handmade molecules "are still a long way down the road," Pethica says.

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