Seminars Archive

Tunable properties of supported metal particles on oxide ultrathin films

Abstract
Ultrathin oxide films on metallic or semiconducting supports are of enormous importance in a variety of fields like corrosion protection of metals, magnetic tunnel junctions, dielectric barriers in metal-oxide field effect transistors, etc. Recently, it has been found that oxide ultrathin films on metal single crystals can exhibit unusual and unprecedented properties which have no counterparts in the corresponding bulk surfaces. For instance, metal atoms or particles deposited on these films can exchange charge with the metal support by direct electron tunneling through the thin dielectric layer. In this talk we will analyze the physical reasons which can lead to charge exchange. In particular, we will focus on the changes in work function of the system which occur when an oxide film is deposited on a metal support and we will consider possible ways to tune the work function so as to induce charge transfers also in those cases where this does not occur spontaneously. We will present cases where adsorbed species become negatively charged (e.g. Au on MgO/Ag), positively charged (e.g. Au on FeO/Pt) or remain neutral (e.g. Au on SiO2/Mo) because of the different position of the Fermi level in the oxide/metal support, and we will discuss methods to modify these interfaces. In particular, we will show that this can be obtained by co-deposition of alkali atoms, and examples of this effect will be reported for Li-doped SiO2/Mo(112) films. Finally, we will show that the occurrence of a charge transfer across the interface can also be used to enhance the magnetic moments of supported Fe clusters.