through a nozzle onto the target. A pulsed valve (General Valve, 5 bar backing pressure of He) which is synchronized with the laser quenches the evaporated atoms into clusters which expand through the nozzle and a skimmer into an oil diffusion pumped vacuum chamber at 10$^{-5}$ mbar. Au clusters (and atoms) are deposited without further mass selection onto a TEM grid placed in the primary beam in a distance of about 40 cm from the nozzle.

The size distribution of the Au particles is shown in the inset of Fig. \[expfig1\](a). Since the only directed acceleration of the clusters is the expansion into the vacuum of the cluster source the impact energy can be considered small enough to avoid intercalation of adsorbate and substrate.

The investigations were conducted on a batch of 8 samples prepared on different days. Four samples were prepared with 300 ablation shots, four with 3000 ablation shots. They were stored individually under air in sealed containers. Experiments were carried out to assure the absence of contamination on the samples (Sec.\[sectiondynamics\]). All samples show the same island formation assuring the reproducibility of the results.

Experimental: transmission electron microscopy {#sectionTEM}
----------------------------------------------

The TEM was carried out with a 