 The 7×7 reconstruction is modeled according to a dimer-adatom-stacking fault (DAS) model constructed by many research groups over a period of 25 years.Extending through the five top layers of the surface, the unit cell of the reconstruction contains 12 adatoms as well as two triangular subunits, nine dimers and a deep corner hole that extends to the fourth and fifth layers.This structure was gradually inferred from LEED and RHEED measurements as well as calculation, and was finally resolved in real space by Gerd Binnig, Heinrich Rohrer, Ch.