| AVS 55th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS1-WeA |
| Session: | Structure of Oxide Surfaces and Oxide Heterostructures |
| Presenter: | T. Risse, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany |
| Correspondent: | Click to Email |
This contribution will focus on the recent efforts to characterize the properties of Au atoms and particles on well ordered MgO films and the ability to tune these properties by modifying the oxide film. The studies are embedded in the current endeavor to correlate the properties of oxide supported Au deposits with their catalytic activity. In this respect the charge state of Au particles has come under scrutiny, in particular after combined theoretical and experimental evidences suggested that nucleation of Au clusters at point defects of MgO leads to a charging of the particles which in turn was made responsible for the enhanced catalytic activity in low-temperature CO oxidation. More recently theoretical calculations predicted that not only defects sites might be able to induce charging of Au atoms and cluster, but the film thickness may serve a suitable parameter to control charging.1,2 In this contribution we present a combined low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), infrared (IR), and electron paramagnetic resonance (EPR) spectroscopic investigation on the properties of gold atoms and clusters adsorbed on well ordered MgO films. These studies aim at providing experimental evidences for the presence of negatively charged Au atoms and particles on these oxide surfaces. First we will focus on the impact of color centers. To this end STM/STS and EPR spectroscopic results will be discussed which can be used to characterize these centers and prove the adsorption of Au particles on them. In combination with IR spectroscopy it possible to show that color centers are indeed capable to donate charge onto Au particles. As a second part we want to discuss the question if the MgO film thickness is a suitable parameter to tune the charge state of Au deposits as predicted theoretically. Thereto low temperature STM experiments of Au atoms and clusters deposited on 3 ML and 8 ML thick MgO films will be discussed to find evidences for a charge transfer for 2-3 ML thick MgO films.
1 G. Pacchioni, L. Giordano, M. Baistrocchi, Phys. Rev. Lett. 94, 226104 (2005).
2 D. Ricci, A. Bongiorno, G. Pacchioni, and U. Landman, Phys. Rev. Lett. 97,036106 (2006).