BioEd Online

Ever since Don Eigler spelled out the letters 'IBM' using 35 xenon atoms in 1989, nanotechnology researchers have strived for ever more control over the building blocks of matter.

That control has now reached a new level. Instead of moving atoms individually, IBM scientists say that they can change their electrical charge, electron by electron.

"People have been moving atoms around for ten years. Here they go one step further, leaving the atoms where they are but changing their status," says Karsten Horn, a physicist at the Fritz Haber Institute of the Max Planck Society in Berlin, Germany.

The electrical charge of an atom is one of its most fundamental properties. It influences the way the atom reacts with the rest of the world, and also how the atom transfers electricity to its neighbours.

Jascha Repp, a physicist at IBM's Zurich Research Laboratory in Switzerland, and his team used a scanning tunnelling microscope (STM) to deliver a single electron to individual gold atoms, giving each one a negative charge. Invented in the 1980s, an STM contains a tip that narrows to an atom-sharp point. As the microscope scans over a surface, individual atoms change the electrical current flowing through the tip.

Scientists normally use this information to build a three-dimensional map of the atomic bumps and hollows on a surface. But Repp's research, published in Science¹ this week, proves that the tip can also deliver electrons to the surface atoms as it moves across them, with exquisite precision. The STM can also go back over the gold atoms and sense whether they are neutral or negatively charged.

Repp's team plans to use the technique to test new materials for useful electrical properties. "On the long timescale, we are trying to find alternatives to conventional semiconductors," says Repp. "Electronics on the atomic-length scale gives you components that are 10,000 times smaller and that create a lot less heat."

He adds that a string of neutral and negative gold atoms could theoretically store information, like the series of 'on' or 'off' switches that forms the basis of binary computing. But he admits that such a device may be decades away from reality.

Writing with atoms

Don Eigler's 1989 piece of nano-art was a key moment in the development of the nascent science of nanotechnology. It proved that applying a voltage to the tip of an STM could transform the microscope into a pair of tweezers to move individual atoms around².

At the time, Eigler could only make his atoms sit still at a frosty -269 °C, just four degrees above absolute zero, the coldest temperature possible. At higher temperatures the thermal energy of the atoms caused them to dislodge from the surface.

But his experiment laid the foundations for the manipulation of molecules at room temperature, which was achieved just a few years later³. Repp has carried out his experiments at about -269 °C, but he hopes that progress in atom charging will turn up the heat just as quickly.

"This has wonderful potential for science. Lots of scientists will read this paper and rush off to try it out for themselves in the lab," says Horn.