AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS3-MoA

Paper SS3-MoA9
Charge Exchange between Alkali Ions and Nanocrystal Metal Surfaces

Monday, November 3, 2003, 4:40 pm, Room 328

Session: Structure and Reactivity of Metal Clusters
Presenter: G. Liu, University of California, Riverside
Authors: G. Liu, University of California, Riverside
J. Yarmoff, University of California, Riverside
Correspondent: Click to Email
Au nanocrystals grown on TiO@sub 2@(110) possess unique catalytic properties, which depend on the cluster size.@footnote 1@ Presumably, the catalytic properties are the result of the electronic configuration of the nanocrystals. Earlier, we showed that the probability for neutralization of low energy alkali ions scattered from metal surfaces is determined by the local electrostatic potential (LEP) a few Å's above the scattering site.@footnote 2@ In the present work, we are using the charge exchange between alkali ions and metallic nanocrystals as a probe of their electronic structure. 2 keV @super 23@Na@super +@ ions were scattered from Au nanocrystals grown on TiO@sub 2@(110), and the neutral fractions of the Na particles singly scattered from Au were measured with time-of-flight. As the average size of the Au nanoclusters increases, the neutral fraction decreases until a uniform Au film is formed. The neutral fraction of Na scattered from bulk Au is very small (~2%) due to the large work function of Au. For small Au clusters, however, the neutral fractions can be as high as 30% or more. The high neutral fraction of the small Au clusters suggests that the alkali ions are coupling to electronic states that are specific to the nanocrystals. The work function change, measured as a function of cluster size, shows a smooth change from the clean TiO@sub 2@(110) surface to that of bulk gold. In order to understand the influence of the work function on the neutral fraction, Cs was deposited onto Au/TiO@sub 2@(110) surface to controllably decrease the work function. In addition, the dependence of the neutral fraction on the ion exit angle and energy was studied. @FootnoteText@ @footnote 1@X. Lai, T. P. St. Clair, M. Valden, and D. W. Goodman, Prog. Surf. Sci. 59 (1998) 25.@footnote 2@C. B. Weare and J. A. Yarmoff, Surf. Sci. 348 (1996) 359.