Evolution and Degeneration of Dimer-Adatom-Stacking-Fault Structure in Solid-Phase Epitaxy on Si(111) Surface Observed by Scanning Tunneling Microscopy

Large unit cells of dimer-adatom-stacking-fault structure and related2 × 2and c(4 × 2) reconstructions have been prepared by low-temperature solid-phase epitaxy and observed by scanning tunneling microscopy. The size-different unit cells of the DAS structure are considered to be a structure evolution in which more electron charge transfers in a larger unit cell from the adatom dangling bonds to the rest-atom dangling bonds. In some cases the DAS structure can degenerate into triangular2 × 2domains and bundlinke c(4 × 2) domains. The rest atoms are always fully filled by electrons due to the charge transfer. The adatom dangling bonds are partially filled in a c(4 × 2) symmetry and essentially empty in a2 × 2symmetry. As a result, the rest atoms in2 × 2domains can be imaged without the adatom protrusions while in the c(4 × 2) domains the protrusions of the adatoms and the rest atoms appear in zigzag chains, when the sample is negatively biased.