AVS 56th International Symposium & Exhibition
    Surface Science Friday Sessions
       Session SS1-FrM

Paper SS1-FrM9
Ion Scattering Studies of Isolated Au Nanoclusters

Friday, November 13, 2009, 11:00 am, Room M

Session: Nanoclusters, Organics and Beam Induced Chemistry
Presenter: R.D. Gann, University of California, Riverside
Authors: S. Balaz, University of California, Riverside
J.A. Yarmoff, University of California, Riverside
R.D. Gann, University of California, Riverside
Correspondent: Click to Email
Isolated Au nanoclusters are grown atop amorphous solid water (ASW) at low temperature. This process, which represents the first step in the growth of nanoclusters via the buffer layer assisted growth (BLAG) method, is a unique way in which to fabricate small deposited clusters that have minimal interactions with a substrate. Such clusters are able to serve as model systems for investigations of how nanocluster electronic structure depends on shape and size. Low energy alkali ion scattering was used to probe the atomic and electronic structures of the clusters in situ. ASW was first deposited as a separation layer onto SiO2/Si(111) at liquid nitrogen temperature, and then Au was evaporated onto the ASW to form nanoclusters. The mean size of the clusters is expected to increase with increased Au deposition. Time-of-flight (TOF) spectroscopy was used to collect charge-resolved spectra of scattered 2 keV 7Li+ and 39K+ ions. Spectra collected following small Au depositions display only a sharp single scattering peak, while multiple and plural scattering features are present following larger depositions. The change in spectral shape is indicative of the formation of multilayer nanoclusters. The experimental findings are interpreted with the aid of Monte-Carlo ion scattering simulations. The neutral fraction of scattered K+, which provides an indication of the filled quantum states, starts at ~50% for small Au coverages and decreases with further deposition, indicating changes in the quantum state occupancy with cluster size. The lack of any angular dependence to the neutralization implies that the clusters behave as atomic-like structures. Further experiments will investigate how the clusters evolve when deposited onto the substrate by heating to desorb the ASW layer.