Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 12: Symposium: Size-Selected Clusters at Surfaces I
(Invited Speakers: Karl-Heinz Meiwes-Broer, Heinz Hövel, Thorsten Bernhardt)

O 12.8: Vortrag

Montag, 25. Februar 2008, 16:15–16:30, MA 005

Thermally activated processes for mass selected Ag clusters on 1 and 2 monolayers C₆₀ on Au(111) — •S. Duffe¹, L. Patryarcha¹, T. Richter¹, B. Sieben¹, H. Hövel¹, C. Yin², B. von Issendorff², and M. Moseler^3,4 — ¹Technische Universität Dortmund, Experimentelle Physik I — ²Universität Freiburg, Fakultät für Physik — ³Fraunhofer-Institut für Werkstoffmechanik IWM, Freiburg — ⁴Freiburg Materials Research Center

We deposited at 165 K mass selected clusters from Ag_{147 ± 1} to Ag_{561 ± 5}, expected to form geometrically magic icosahedra, on 1.7 ML C₆₀/Au(111). On 1 and 2 ML C₆₀ we observed very narrow cluster height distributions. After annealing, the clusters on 2 ML C₆₀ kept their original height for more than 12 hours at room temperature (RT). In contrast the clusters on 1 ML C₆₀ decayed and disappeared at RT [1]. During the decay process we observed a metastable size with the height of 1.7 nm for different initial cluster sizes. Neither Ag₅₅ with h=(1.5 ± 0.2) nm nor Ag₁₄₇ with h=(2.0 ± 0.2) nm after deposition at 165 K corresponded to the peak at h=1.7 nm. Therefore we deposited Ag₈₀ and Ag₆₈ at 165 K and observed cluster heights of ≈ 1.5 nm on 1 and 2 ML C₆₀ for both cluster sizes, probably due to their prolate shape. The subsequent annealing of the clusters up to RT caused a change of the cluster height distribution, probably due to Ostwald ripening, and the metastable size with the height of 1.7 nm was formed. Thus mass selected geometrically non-magic Ag clusters show a different behavior at RT as geometrically magic Ag clusters.

[1] S. Duffe et al., Eur. Phys. J. D (2007), published online