FIGURE 3. Transformation of the passivation layer into Au islands.

a, The ultrathin layer gives rise to a broad intensity distribution along q. With both in-plane peaks present, the pure gold peak in the corresponding q-scan has a much narrower width, indicating an island height of typically 10–15 monolayers (2–3 nm). The ultrathin passivation layer is transforming into Au islands, maintaining predominantly the initial CBA stacking. b, By increasing the potential above 300 mV on the timescale of hours, an in-plane peak at a q position close to epitaxial gold is emerging in addition to the ultrathin passivation layer peak. c, Ex situ atomic force microscope image (0.5 m 0.5 m) after applying a potential of 450 mV versus Ag/AgCl; in this potential regime the formation of 2–3-nm-thick pure Au islands was observed in the X-ray diffraction experiments, which is a typical corrugation of the surface. d, Height along the line segment in c. The typical lateral dimension of the islands is 20 nm. The measured vertical corrugation of 1.5 nm is probably limited by tip effects.