because of their low contrast on the amorphous substrate. Panel (b) shows a typical island formed after the sample has been aged for four months. The reproducibility of the results is assured since eight samples of different coverage prepared on different days stored in individual sealed containers show the same phenomenon.

![\[expfig1\] *TEM images of Au clusters deposited on an a-C substrate by laser ablation (3000 shots): (a) sample one day after its preparation. The inset shows the histogram of the size-distribution of the clusters. Clusters smaller than 1nm in diameter cannot be resolved unambiguously within the TEM images. (b) Typical island of higher contrast formed on a sample four months after its preparation. (c) Detail of the island displayed in panel (b). The areas circled show regions exhibiting crystalline structures with differently spaced lattice planes.* ](expfig1.eps){width="45.00000%"}

While the formation of small islands on short time scales has been observed previously for larger size-selected clusters for Co on microgrid substrates,[@PKW+01] for Au on amorphous carbon,[@EHD02] as well as for Ag on graphite,[@CPP03] the new features here are dark areas typically covering 25$\times$70 nm$^2$ underlying the larger clusters. As described in this paper in detail we were able to identify these 