Bi-induced (√3 x √3)R30° structures formed on the Si(111) surface were studied using scanning tunnelling microscopy and low-energy electron diffraction. Three distinct phases: monomer, trimer and honeycomb phases were identified for the first time by scanning tunnelling microscopy, depending on the Bi coverage, even though the √3 x √3 symmetry was always preserved in the low-energy electron diffraction observation. At low coverages, Bi atoms were found to occupy the T4 site. In this adsorption geometry, a monomer phase (α-phase) were formed stably up to an ideal coverage of 1/3ML. In trimer symmetry (β-phase) at saturation coverage of 1ML, the individual atoms of the Bi clusters were clearly resolved. Between these two coverages, however, a honeycomb-type √3 x √3 reconstruction was also found, by scanning tunnelling microscopy, to co-exist with the trimer phase. This result reveals a new coverage dependent reconstruction process involving the √3 x √3 reconstruction of Si(111) surface.

Scanning Tunnelling Microscopy of √3x√3-Bi Reconstruction on the Si(111) Surface. C.Park, R.Z.Bakhtizin, T.Hashizume, T.Sakurai: Japanese Journal of Applied Physics, 1993, 32, L290-3