Paper SS1-MoM12
TiO₂ with Buried Ag Nanoclusters for Photocatalysis¹

Monday, October 15, 2007, 11:40 am, Room 608

Many metals readily form nanoclusters on TiO₂ and these clusters can have unusual optical and catalytic properties. The lifetime of these clusters can be limited when exposed to an electrochemical environment, so it can be desirable to bury these metallic clusters in a protective oxide layer. Although the clusters do not participate directly in chemical reactions, optical excitations allow them to provide hot electron-hole pairs to the near surface region to stimulate surface chemistry. We will present a multiple-technique surface study of overcoating Ag nanoclusters on TiO₂(110) with titania using STM, EELS and synchrotron-based resonant photoemission. STM measurements show that Ag readily forms 5-10 nm clusters on TiO₂(110) and EELS measurements show that the bare clusters on TiO₂(110) exhibit a sharp plasmon resonance at 3.7 eV. As the cluster density increases, the underlying substrate bandgap is reduced while the bandgap excitation cross-section increases. These Ag clusters are then buried by coating with a thin layer of Ti that is subsequently oxidized. Within the dielectric medium of the oxide, the plasmon resonance is broadened and red-shifted as shown by EELS. Synchrotron-based resonant photoemission has been used to study the electronic structure of the clusters, both bare and with and the titania overcoat. The valence electronic structure and the origin, whether Ti or Ag-induced, of the bandgap defect states within the titania are identified by tuning over photoemission resonances. The role of these bandgap states in determining the surface optical properties and photochemistry will be discussed.

¹We would like to acknowledge the support of the LSU CAMD synchrotron light source and the support of NSF through CHE-0615606.