| Popis: |
Silver clusters up to 1000 atoms in size, on an amorphous carbon film, have been exposed to ambient air and investigated by atomic resolution imaging in the aberration-corrected Scanning Transmission Electron Microscope (ac-STEM). Ordered structures comprise more than half the population, the rest are amorphous. Of ordered isomer structures the most common is the icosahedron. The results contrast with the published behaviour of silver clusters protected from atmospheric exposure, where the predominant ordered isomer is face-centred cubic. We propose that the formation of surface oxide or sulphide species resulting from air exposure can account for this isomer switching. This interpretation is consistent with density functional theory calculations based on silver nanoclusters, in the size range 147-201 atoms, on which methanethiol molecules are adsorbed. An understanding of the effects of ambient exposure on the atomic structure and therefore functional properties of nanoparticles is highly relevant to their real-world performance and applications. |
