AVS 51st International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM6
Thermodynamically Controlled Self-Assembly of Oxide Nanostructures@footnote *@

Wednesday, November 17, 2004, 10:00 am, Room 210B

Session: Metal Oxides and Clusters I: Formation and Structure
Presenter: F.P. Netzer, University of Graz, Austria
Authors: F.P. Netzer, University of Graz, Austria
J. Schoiswohl, University of Graz, Austria
M Sock, University of Graz, Austria
G. Kresse, University of Vienna, Austria
S. Surnev, University of Graz, Austria
M.G. Ramsey, University of Graz, Austria
Correspondent: Click to Email
The fabrication of surface-supported nanoscale oxide materials in low dimensions via a chemically driven self-assembly process of novel oxide cluster molecules is reported. As opposed to usual molecular self-assembly, where the construction units are deposited directly from the gas phase, the oxide building blocks with a unique stoichiometry and structure form spontaneously on a Rh(111) metal surface. These can be organised into different two-dimensional oxide structures by careful adjustment of the chemical potential of oxygen µ@subO@, allowing the controlled design of oxide nanostructures on a metal surface. This is demonstrated by following, at the atomic level, the formation and aggregation of planar vanadium oxide V@sub6@O@sub12@ clusters. The planar V@sub6@O@sub12@ cluster molecules form under appropriate conditions of µ@subO@ and of the vanadium concentration at the Rh(111) surface. The structure and stability of these hexagonal V@sub6@O@sub12@ clusters have been elucidated by STM and density functional theory (DFT) calculations. The V@sub6@O@sub12@ structures do not exist in the gas phase and constitute a novel kind of cluster material, that is stabilised by the metal-cluster interface. The V-oxide clusters are mobile at elevated temperature and their surface diffusion has been studied in variable-temperature STM experiments: the diffusion parameters indicate diffusion of the entire clusters. The V@sub6@O@sub12@ units can be organised by self-assembly into different 2D oxide structures, depending on µ@subO@. The assembly process occurs via a reductive or oxidative condensation process, which involves strong chemical bonding interactions with partly covalent and ionic character. Nevertheless, the here reported aggregation is reversible, and by adjustment of µ@subO@ and the Rh surface temperature the V@sub6@O@sub12@ clusters can be regenerated from the oxide islands by 2D re-evaporation. @FootnoteText@ @footnote *@ Work supported by the Austrian Science Funds.