Direct atomic imaging and dynamical fluctuations of the tetrahedral Au(20) cluster.

We report real-space, atomic-resolution images of Au(20) clusters obtained with the aberration-corrected Scanning Transmission Electron Microscopy. The proposed tetrahedral (FCC segment) pyramid structure is confirmed. The clusters cycle between isomers under the electron beam in the time-lapse images acquired. Disordered variants on the high symmetry forms are commonly observed. We believe that the direct experimental identification of these kinds of atomic structure, and the fluctuations between them, is fundamental to our understanding of nanoparticle structures, as well as applications such as heterogeneous catalysis.