IBM probe detects an atom's charge

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 tunnelling microscopes, though, require a conducting substrate beneath the molecule in question, IBM said.

This image is a model of the experimental setup for the atomic probe. The gold atom is on a substrate covered with a very thin insulating film of sodium chloride, which also stabilises the charged atom.

IBM has posted a video on the experiment at YouTube.