Book of Abstracts Book of Abstracts - Universität Konstanz

A - 34
152
Supported Gold Clusters and Cluster-Based Nanoparticles:
Characterization, Stability and Growth Studies by In Situ Grazing
Incidence Small Angle X-ray Scattering Technique
Stefan Vajda 1 , Jeffrey W. Elam 2 , Byeongdu Lee 3 , Michael J. Pellin 4 , Sönke Seifert 3 , George Y.
Tikhonov 1 and Nancy A. Tomczyk 1 , Randall E. Winans 1,3
1 Chemistry Division, 2 Energy Systems Division, 3 Experimental Facility Division, and 4 Materials Science
Division
Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 6043, USA
Supported clusters possess unique, strongly size-dependent properties. However, the
Achilles heal of supported particles remains their sintering at elevated temperatures or when
exposed to mixtures of reactive gases. In this paper, the issue of thermal stability and
agglomeration of atomic gold clusters and nanoparticles produced by cluster deposition on
oxide surfaces is addressed as a function of deposited cluster size, level of surface coverage,
temperature and time of heat treatment by synchrotron X-ray radiation at the Advanced Photon
Source.
The continuous beam of gold clusters was generated in a laser vaporization source. The Aun +
clusters were deflected into setup with an incorporated mass spectrometer for the pre-selection
of narrow cluster distributions in the size range Aun + , n=2,…10, with 1 to 5 dominant sizes. As
support, silica as well as Al2O3 and TiO2 films grown by atomic layer deposition on
SiO2/Si(111) were used. Coverages up to 45% of atomic monolayer equivalents were employed.
The temperature region of aggregation was determined by gradually heating up the samples and
recording 2-D X-ray scattering images during the heat treatment. The analysis of the data
provides information about the average size and shape of supported particles [1].
The size of the nanoparticles formed on the surface upon cluster deposition and their thermal
stability exhibited a very strong dependence on the initial size of the clusters, level of surface
coverage and material of the support. When applying surface coverages higher than 5% ML,
aggregation of the clusters into nanometer-size particles with narrow size distribution prevailed.
With decreasing coverage, the fraction of not-aggregated clusters significantly increased. Heat
treatment led to final particle sizes determined by initial cluster size, coverage and length of
treatment. The most striking results were observed when depositing 2.5 % ML of Au7-Au10
clusters on SiO2/Si(111): particles of one size, corresponding to Au20 were formed. Moreover,
these particles exhibited extraordinary and unexpected thermal stability as well, not undergoing
aggregation until 400 °C, when an onset of a slow agglomeration takes place [2]. Work on
supported clusters of single size and in reactive gas atmosphere is currently under progress.
This work and use of APS was supported by the U.S. Department of Energy, Office of Basic
Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under contract
number W-31-109-ENG-38.
References
[1] R. E. Winans, S. Vajda, B. Lee, S. J. Riley, S. Seifert, G.Y. Tikhonov, N. Tomczyk, J. Phys.
Chem. B, 108, 18105 (2004).
[2] S. Vajda, R. E. Winans, J.W. Elam, B. Lee, M.J. Pellin, S.J. Riley, S. Seifert, G.Y. Tikhonov and
N. A. Tomczyk, invited paper, submitted to ACS.