Chemical shifts and cluster structure

The 2p core-level electron binding energies of size-selected silicon cluster ions have been determined from soft x-ray photoionization efficiency curves. Local chemical shifts and global charging energy contributions to the 2p binding energy can be separated, because core-level and valence-band electron binding energies exhibit the same inverse radius dependence. The experimental 2p binding energy distributions show characteristic size-specific patterns that are well reproduced by the corresponding electronic density of states obtained from density functional theory modeling. These results demonstrate that 2p binding energies in silicon clusters are dominated by initial state effects, i.e., by the interaction with the local valence electron density, and can thus be used to corroborate structural assignments

An experimental setup for nondestructive deposition of size-selected clusters

An experimental setup for the deposition of mass-selected clusters using a laser vaporization source and a magnetic field mass selector is presented. Nondestructive deposition and a coverage of 1% of a monolayer within 5 h are achieved for mass-selected metallofullerene clusters as demonstrated for deposited Ce@C-60 on highly oriented pyrolytic graphite. (C) 2002 American Institute of Physics

Combining Theory and Experiment to Characterize the Atomic Structures of Surface-Deposited Au309Clusters†

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 AuN, clusters with N ) 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