IBM atomic probe gets newly sensitive touch

IBM's atomic force microscope now can distinguish charged gold atoms from neutral ones. Big Blue hopes that will help with nanocomputing and solar energy research.

IBM already had technology that could measure extremely subtle forces among atoms, but a nanotechnology development a the company's Zurich Research Laboratory shows a new level of sensitivity: the ability to distinguish positively charged atoms from those that are neutral or negatively charged.

The atomic force microscope maps what's below by detecting subtle changes in forces of attraction.
The atomic force microscope maps what's below by detecting subtle changes in forces of attraction. IBM

Researchers at the Zurich lab, along with colleagues at the University of Regensburg and Utrecht University, used an atomic force microscope (AFM) with a tuning-fork detector arrangement on the tip of its probe to distinguish among gold atoms that were positively charged, neutral, or negatively charged. The researchers describe their approach in the June 12 issue of Science.

"The AFM with single-electron-charge sensitivity is a powerful tool to explore the charge transfer in molecule complexes, providing us with crucial insights and new physics to what might one day lead to revolutionary computing devices and concepts," said Gerhard Meyer, who IBM's work with the AFM and its precursor, the scanning tunneling microscope (STM), in a statement.

Just how sensitive, exactly? IBM says the arrangement can detect a force less than 1 piconewton, which for comparison is the force of gravitational attraction of two adults a half kilometer apart. And according to Wolfram Alpha, it takes a force of 65 piconewtons to pull a strand of DNA apart by pulling on each end.

IBM has been steadily advancing its atomic-level research for years, using its technology to detect, move, and now study individual atoms. This nanotechnology research is far from practical today for the holy grail of nanotechnology, mass-producing devices by assembling them atom by atom, but it's a step in that direction.

Differences in the frequency that a tuning-fork arrangement on IBM's atomic force microscope can distinguish between charged and uncharged gold atoms.
Differences in the frequency that a tuning-fork arrangement on IBM's atomic force microscope can distinguish between charged and uncharged gold atoms. IBM

The new technology could help with a variety of research areas, IBM argues: molecular electronics for nanocomputing devices, catalysis of chemical reactions, and the inner workings of solar cells' conversion of light energy into electrical energy.

"Mapping the charge distribution on the atomic scale might deliver insight into fundamental processes in these fields," said IBM researcher Leo Gross.

It's hard to precisely study individual atoms--the warmer the temperature, the more they jiggle. To reach the new sensitivity level, the researchers had to chill their experimental apparatus to 5 kelvin, or minus 451 Fahrenheit.

An atomic force microscope works by measuring the attractive force between its tip and atoms below. To achieve greater sensitivity, the researchers attached a two-prong tuning fork that vibrates at a certain natural frequency. Moving it closer to atoms subtly speeds or slows this natural resonant frequency.

One reason the research is significant: molecular electronics use substrates that don't conduct electricity. Scanning tunneling microscopes, though, require a conducting substrate beneath the molecule in question, IBM said.

 

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