Softlanding of Ag309 and Ag561 clusters on a C60 monolayer at low temperatures and the observation of thermally activated cluster decay

Hoevel, Heinz; Duffe, Stefanie; Irawan, Thomas; Bieletzki, Markus; Richter, Torsten; Sieben, Benedikt; Yin, Chunrong; von Issendorff, Bernd; Moseler, Michael Germany

Mass selected Ag⁺_561±5 and Ag⁺_309±3 clusters were deposited with low kinetic energy on an Au(111) surface functionalized with an ordered monolayer of C₆₀ molecules. This substrate system proved to be a new and promising choice for the investigation of mass selected clusters attached to a surface. Stable cluster samples could be obtained for deposition at a temperature of 165 K, which in STM images measured at 77 K gave an extremely narrow height distribution with (3.1±0.2) nm and (2.6±0.2) nm cluster height, respectively. Molecular dynamics simulations of the deposition suggest that the experimental conditions indeed are close to softlanding with only minor distortions of the icosahedral cluster shape at the cluster-fullerene interface. After annealing the samples up to room temperature we observed thermally activated cluster decay and penetration of the Ag material though the C₆₀ film. We compared these data with results which we obtained for Ag islands produced by the deposition of Ag atoms at low temperatures and subsequent annealing. In this case the Ag material reorganizes into larger islands for annealing up to room temperature, which is in sharp contrast to the decay for the deposited clusters. Very interesting is the appearance of a sharp maximum at about 1.7 nm cluster height during the decay of the deposited clusters, which was also observed for room temperature deposition of Ag⁺_561±5 and Ag⁺_309±3 clusters. This seems to be an indication for some ‘magic’ cluster size in the cluster-surface system.

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