| AVS 54th International Symposium | |
| Surface Science | Monday Sessions |
| Session SS1-MoM |
| Session: | Catalysis on Clusters and Nanoparticles |
| Presenter: | T. Risse, Fritz-Haber-Institut der MPG, Germany |
| Authors: | T. Risse, Fritz-Haber-Institut der MPG, Germany M. Sterrer, Fritz-Haber-Institut der MPG, Germany M. Heyde, Fritz-Haber-Institut der MPG, Germany N. Nilius, Fritz-Haber-Institut der MPG, Germany G. Pacchioni, Universita di Milano-Bicocca, Italy H.-J. Freund, Fritz-Haber-Institut der MPG, Germany |
| Correspondent: | Click to Email |
The catalytic activity of Au clusters deposited on oxide supports is extensively studied in recent years. There is evidence that the charging of Au particles may play an important role in this respect. In particular, combined theoretical and experimental evidence shows that nucleation of Au clusters at point defects of MgO leads to a charging of the particles and this may be connected with the enhanced catalytic activity in low-temperature CO oxidation. According to theoretical calculations a similar charging is expected for Au deposits on very thin MgO films of a few monolayer.1,2 In this contribution we present a low-temperature scanning tunneling microscopy investigation on the properties of gold atoms and clusters adsorbed on ultrathin MgO films grown on a Ag(001) single crystal surface. The gold adsorption was studied at 5-10 K using MgO films of different thickness to provide experimental evidence for the theoretically predicted charging of gold atoms and clusters on very thin films. The adsorption of Au on a 3 ML thin MgO film leads to a preferential ordering of Au atoms revealing a repulsive interaction between the Au atoms which is consistent with the expectation for charged atoms. On the contrary Pd atoms which are predicted to be neutral show a statistical nucleation behavior. In addition, it is found that the adsorption sites of Au atoms change when changing the thickness of the MgO film from 8 ML to 3 ML perfectly in line with the theoretical predictions. Whereas Au clusters on bulk MgO or thick films are expected to grow as 3-dimensional islands, their counterparts on thin MgO films are expected to from 2-dimensional islands. Annealing experiments of Au deposited at 5-10 K show that this crossover in dimensionality does exist for Au particles in the thickness range of 3 ML to 8 ML of the MgO films.
1G. Pacchioni, L. Giordano, M. Baistrocchi, Phys. Rev. Lett. 94, 226104 (2005).
2D. Ricci, A. Bongiorno, G. Pacchioni, and U. Landman, Phys. Rev. Lett. 97,036106 (2006).