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Morphologies Studies of Mass Selected Au Clusters on Rutile TiO2 as a
Function of Impact Energy and Surface Temperature
P. Convers, R. Vallotton, R. Monot, W. Harbich
Institut de Physique des Nanostructures,
Ecole polytechnique Fédérale de Lausanne (EPFL),
CH-1015 Lausanne
In 1989 Haruta and coworkers have shown that small gold particles (diameter < 4 nm) are
catalytically active [1]. Gold was found to be even more efficient for temperatures below 400°C
than Pt, usually used for CO oxydation [2, 3]. More recent studies by Heiz et al. (Mass selected
Aun deposited on MgO) and Anderson et al. (Mass selected Aun deposited on TiO2) report a
pronounced size dependence of the catalytic activity [4, 5]. However informations on the
morphology of the clusters is sparse. Wahlström et al. showed that atomic Au thermally
deposited on a surface of TiO2(110) form clusters that are stabilized by oxygen vacancies at the
surface [6]. The clusters are small enough for catalysis, however a temperature increase causes a
sintering of the clusters and probably decreases the catalytic efficiency.
To understand the clusters morphology as a function of temperature, we deposit mass-selected
gold clusters with defined kinetic energy on a TiO2(110). The morphology is then studied by
STM after different heating cycles up to 1000 K. We observe that large cluster sizes (n = 7) and
high deposition energy (up to 4500 eV ) stabilize gold on the surface. Figure 1 is a typical STM
image of a deposit of Au7 on TiO2 at 20 eV after a heating cycle at 800 K.
References
Figure 1. Au 7/TiO 2 at 20eV after annealing at 800K
[1] M. Haruta, N. Yamada, T. Kobayashi, and S. Iijima, Journal of Catalysis 115, 301 (1989).
[2] M. Haruta, Catalysis Today 36, 153 (1997).
[3] M. Valden, X. Lai, and D. W. Goodman, Science 281, 1647 (1998).
[4] A. Sanchez, S. Abbet, U. Heiz, W.-D. Schneider, H. Häkkinen, R. N. Barnett, and U. Landman, J.
Phys. Chem. A 103, 9573 (1999).
[5] S. Lee, C. Fan, T. Wu, and S. L. Anderson, J. Am. Chem. Soc. 126, 5682 (2004).
[6] E. Wahlstrom, N. Lopez, R. Schaub, P. Thostrup, A. Ronnau, C. Africh, E. Laegsgaard, J.
Norskov, and F. Besenbacher, Phys. Rev. Lett. 90, 026101 (2003).
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