Physics: Charging atoms, one by one

The scanning tunneling microscope (STM) made it possible to manipulate atoms and move them around. Now researchers are discovering how to alter the chemical properties of individual atoms. In his Perspective, Horn discusses results reported in the same issue by Repp et al. in which the charge state of individual gold atoms deposited on a sodium chloride surface was changed. By means of a voltage pulse from an STM tip, atoms were switched from a neutral state to a negative ionic state and back again. In addition to providing a system to study the fundamental properties of single atoms, the ability to switch charge state may offer new ways to alter surface chemical reactions or store data at high bit density