Charge transfer and rest-atom imaging in dimer-adatom-stacking-fault structure evolution observed by scanning tunnelling microscopy on the Si(111) surface

Abstract

Large unit cells of dimer-adatom-stacking-fault (DAS) structure and related (2 × 2) and c(4 × 2) reconstructions have been prepared by low temperature solid phase epitaxy and observed by scanning tunnelling microscopy. The development of larger unit cells of the DAS structure is considered to be a structure evolution in which more electron charge transfers from the adatom dangling bonds to the rest-atom dangling bonds. In some cases the DAS structure can degenerate into triangular (2 × 2) domains and band-like c(4 × 2) domains. The former are located on a faulted layer while the underneath bilayer of the latter can consist of alternating faulted and unfaulted strips. The rest atoms are always fully filled by electrons due to the charge transfer. The adatom dangling bonds are partially filled in the c(4 × 2) domains and essentially empty in the (2 × 2) domains. As a result, the rest atoms in (2 × 2) domains can be imaged without the adatom protrusions while in the c(4 × 2) domains protrusions of both appear in zigzag chains in filled-state images, when the sample is negatively biased.