Philips CM200 FEG/ST electron microscope at an energy of 200 keV equipped with a Noran Ge detector system for energy-dispersive X-ray analysis (EDX). A Gatan 652 Double Tilt Heating Holder operated by a Gatan 901 SmartSet Hot Stage Controller was used to perform the in situ annealing experiments.

Transmission electron holography was carried out using a Möllenstedt biprism installed in the selected-area aperture holder of the microscope. The electrostatic potential of the biprism wire was close to 150 V. The images recorded were analyzed using the phase shift of the (000)-beam of the first hologram sideband. Data analysis was performed using the DALI program package,[@RKR+96] which was extended for the reconstruction of holograms. The details of the reconstruction of holograms are outlined by Lichte and Lehmann.[@LL02]

Figure \[SampleHologram\] shows the three-dimensional visualization of the phase shift[@Phasesign] with respect to the vacuum $\Delta\phi$ observed on a 28.2$\times$28.2 nm$^2$ surface segment of a typical sample. In the far right corner a part of an island as shown in Fig. \[expfig1\](b) is visible. In the front left corner the linear decrease of the thickness of the substrate near the substrate edge is visible. All holographic images were taken at substrate edges in order 