Deciding whether a substance is, say, steel, brick, wood or plastic is easy--but not on the atomic scale, which lacks information about such everyday characteristics. Using an atomic-force microscope (AFM), however, an international team of physicists has developed a method of atomic "fingerprinting" that can determine the chemical identity of individual atoms on a surface mixed with all of them.

"Until now, there was not any technique that would allow us to identify atom by atom and see them at the same time," says Rub?n Per?z of the Autonomous University in Madrid. Using their AFM approach, Óscar Custance and his collaborators at Osaka University, along with Peréz and his colleagues and others, could discern tin, silicon and lead, which are all chemically similar. The resulting image of the atoms resembles a granulated painting, where the "grains"--the individual atoms--are distinguishable in false color.