Observing the motion of a single adsorbed atom with picosecond and subnanometer resolution

A new method is described for recording the motion of a single adsorbed atom or molecule in real time, with an ultimate achievable resolution of ${10}^{\mathrm{-}14}$ s. The time dependence of electron field emission through an atom adsorbed on a metal tip is measured by focusing the electrons into a beam, which is swept across a detector screen. Similtaneous temporal and one-dimensional spatial resolution of the dynamics is possible. The motion of single Cs atoms between sites on atomically characterized W(111) tips is observed at 2 ps resolution.