The stepped Si(111) surface after 0.2 ML of gold deposition at 900⁰C in ultrahigh vacuum and subsequent cooling to room temperature. The cooling results in the coalescence of adatoms on the terraces into the monolayer islands.
For the first time it was experimentally directly observed the increase of adatom concentration as a result of self interstitials nucleation and emerging to the surface due to gold bulk diffusion at high temperature.

Image courtesy of  E.E. Rodyakina, S.S. Kosolobov, D.V. Scheglov, A.V. Latyshev, Institute of semiconductor physics SB RAS, Russia.