By transferring a single electron to a gold atom, scientists have converted a neutral atom into a negatively charged ion. The switching of the electronic state of an individual atom is not only a demonstration of the exquisite control over matter that scientists now wield but could also lead to new ways of encoding data for making ultrahigh-density memory chips.
Jascha Repp of the IBM Zurich Research Laboratory in Switzerland and his colleagues allowed gold atoms to adsorb onto a thin film of sodium chloride atop a copper base. Then, they finessed the styluslike tip of a scanning tunneling microscope to a position directly over one gold atom and applied a positive-voltage pulse. This pulse delivered an electron to the atom, tagging the gold a