with HRTEM.

While the exact determination of the origin of the aforementioned patterns from the present data is not possible, it can be speculated that the Au film exhibits a similar reconstruction as has been observed for Au(111) surfaces by scanning tunneling microscopy (STM) measurements,[@HCZC95; @HCR+87] where superstructures with a similar modulation[@HKS+81] ($\sqrt{3} \times {\rm lattice\ constant}
\approx 500$ pm) have been observed. The presence of Au(111) surfaces is also consistent with the MC simulations (Sec.\[sectionMCfilm\]). Moreover, reconstruction pattern have been observed for small islands of Au monolayers on HOPG in ultra high vacuum (UHV) by STM measurements,[@GSC88] but a direct comparison is difficult because of the larger film thickness in our samples (Sec. \[sectionFilmChar\]).

We conclude that the higher contrast areas underlying the islands consist of a few monolayers of Au that form crystalline structures on at least parts of the substrate surface, which in turn must be sufficiently smooth.

Au-film characterization {#sectionFilmChar}
------------------------

In order to get information about the thickness of the observed films, we performed off-axis holography experiments. A three dimensional visualization of a segment of the substrate including a part of an Au island has been shown in Fig. \[SampleHologram\] in Sec.\[sectionTEM\]. Figure \[holoscans\] shows 