AVS 52nd International Symposium
    Surface Science Wednesday Sessions
       Session SS2-WeA

Paper SS2-WeA6
Neutralization of Low Energy Li Ions Scattered from Au Nanoclusters

Wednesday, November 2, 2005, 3:40 pm, Room 203

Session: Reactions on Nanoclusters
Presenter: G.F. Liu, University of California, Riverside
Authors: G.F. Liu, University of California, Riverside
Z. Sroubek, Czech Academy of Sciences
J.A. Yarmoff, University of California, Riverside
Correspondent: Click to Email
Charge exchange during the scattering of low energy (0.5-10 keV) alkali ions provides a sensitive measure of the confined quantum states of nanomaterials. In earlier work, we showed that the neutralization of Na@super +@ scattered from Au nanoclusters correlates with the presence and position of the confined states.@footnote 1@ In this work, we scatter Li ions from Au nanoclusters grown on TiO@sub 2@(110). The neutralization probability of the Li singly scattered from the Au nanoclusters is measured with time-of-flight spectroscopy. Au nanocrystals grown on TiO@sub 2@(110) possess unique catalytic properties, which depend on the cluster size. The size of the clusters is determined by the amount of Au deposited and the surface temperature, and increases with the amount deposited. The neutral fraction was found to have a maximum at ~0.2 ML Au coverage, which is consistent with the maximum seen for the catalytic activity.@footnote 2@ This provides clear evidence that the ion scattering is probing the same states that are responsible for unique properties of these materials. When additional Au is deposited, the neutral fraction first drops to a minimum (at ~10 ML Au), and then increases to the bulk Au value. This shows that ion scattering is able to monitor the formation of the conduction band as a transition is made from isolated clusters to a continuous film. In addition, the dependence of the neutral fraction on the ion exit angle and energy was investigated. In order to better correlate the dependence of the cluster sizes on the neutral fraction, future experiments will involve Li and Na ions scattered from size-uniform nanoclusters grown by chemical synthesis. @FootnoteText@ @footnote 1@G. F. Liu, Z. Sroubek, and J. A. Yarmoff, Phys. Rev. Lett. 92, 216801 (2004). @footnote 2@M. Valden, X. Lai, and D.W. Goodman, Science 281, 1647 (1998).