Paper SS2-WeM10
Tuning the Adsorption Properties of an Oxide Material Via Doping: Au Clusters onto Cr-doped MgO(001) Films

Wednesday, November 2, 2011, 11:00 am, Room 109

The doping of metal oxides has been explored in several investigations with the aim to prepare better materials for catalysis, optics and electronic applications. Doping of wide-gap oxide materials can be realized by the controlled introduction of various types of lattice defects, including point defects such as oxygen vacancies, line defects (e.g. grain boundaries and dislocations) and impurity atoms. In this study, we have exploited photon-scanning tunneling microscopy used in imaging as well as in cathode-luminescence mode to investigate Au clusters supported on thin, single crystalline MgO(001) and Cr-doped MgO(001) films grown on Mo(001). First of all, we have prepared Cr-doped MgO films on a Mo(001) support as a model system for a transition-metal doped wide-gap insulator with interesting applications in catalysis. To elucidate the role of the Cr in the MgO matrix, the morphological and optical properties of the system were analyzed as a function of the Cr load, using the STM. The Cr was incorporated into the film either by Cr-Mg co-deposition in oxygen or post-evaporation followed by an annealing step. From the distinct light emission properties of the doped oxide, a detailed picture has been developed on the Cr⁺³ position inside the MgO lattice and the associated modifications in the electronic structure. The role of the Cr dopants on the adsorption behaviour of the oxide film was investigated by depositing small amounts of Au. While on pristine MgO films, Au nucleates into 3D particles, mainly 2D aggregates form on the doped oxide support. We assign this change in the Au growth mode to charge transfer processes from the Cr centres into the Au clusters and will discuss possible consequences on the chemical activity of the doped metal-oxide system.