Although quantum size effects in $\mathrm{Pb}∕\mathrm{Si}\left(111\right)$ control the selection of uniform island heights, the fast formation time (after deposition of few minutes at $\mathrm{T}\sim 180\mathrm{K}$) has been puzzling so far. By studying the island growth in stepwise deposition experiments, we demonstrate the important role of the wetting layer in the kinetics. Pb is transferred to unstable islands, not by independent atom hops, but by the continuous spreading of the wetting layer from the surrounding area to the island top. As Pb is moved to the top in ring-like morphology the underlying $7\times 7$ reconstruction in the surrounding area emerges gradually.

• Received 24 August 2006

DOI:https://doi.org/10.1103/PhysRevB.75.235443