Spotting Charges Many nanoscale physical systems are sensitive to the position of isolated charges, such as single-electron transistors and molecular assemblies that separate charges with energy from photons. In order to probe the location of a charged atom, the most general methods would work on insulating surfaces. Gross et al. (p. 1428 ; see the Perspective by Meyer and Glatzel ) show that a tuning-fork atomic force microscope (AFM) operating in a noncontact mode at cryogenic temperatures can resolve the charge state of gold and silver atoms absorbed on a sodium chloride film. Charged atoms set up image charges in the AFM tip, which creates an electrostatic force not present with a neutral atom.