Motion of small gold clusters in the electron microscope

The rapid motion of small (∼1000 atom) gold clusters observed with atomic resolution in the electron microscope is argued to be the result of brief melting events, triggered by the Auger decay of an M‐shell vacancy created in a gold atom within the cluster. Each molten episode lasts ∼10 ps, too short for noticeable evaporation. The observed frequency of motion events is shown to be consistent with ionization cross sections for the gold M shell and the electron current densities employed. It is argued from the lack of observable evaporation that the steady‐state temperature of the clusters is ≤1100 K, well below the melting point. The model correctly predicts the cessation of motion at a particle diameter ∼8 nm, when a single Auger decay can no longer melt the cluster.