Source: http://www.nature.com/news/2004/040719/full/040719-14.html
Gold charges up electron by electron
Mark Peplow
Scientists master fresh aspect of atomic manipulation.
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.
References
Repp J., Meyer G., Olsson F. E., & Persson M. Science, 305. 493 - 495
(2004).
Eigler D. M., & Schweizer E. K. Nature, 344. 524 - 526 (1990). | Article |
ISI | ChemPort |
Jung T. A., Schlittler R. R., Gimzewski J. K., Tang H., & Joachim C.
Science, 271. 181 - 184 (1996). | ISI | ChemPort |
©2004 Nature Publishing Group
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