Combining theory and experiment to characterize the atomic structures of surface-deposited Au309 clusters

Gold clusters with icosahedral, decahedral, and cuboctahedral shell structures, have been studied using the Gupta many-body potential, to aid in the structural characterization of surface-deposited Au309 clusters using high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). In this size regime, the calculations indicate that the icosahedral geometries are lower in energy than the decahedral and cuboctahedral structures but that the energy differences are small. This is consistent with the spread of different geometries observed by HAADF-STEM. Analysis of the different outlines and intensity profies of the HAADFSTEM images indicate that there are roughly equal numbers of decahedral and cuboctahedral clusters on the surface. The unambiguous assignment of icosahedral geometries is more difficult because of the more-spherical nature of these nanoparticles. Because the experimental uncertainty in the deposited cluster size is ±5%, a genetic algorithm has been used to search for the lowest energy isomers for Au N clusters with TV = 309 ± 15 atoms. A variety of highly faceted structures have been found, many corresponding to incomplete or distorted icosahedra, including a puckered icosahedral geometry for N = 309.