Scanning Tunneling Microscopy of √3×√3-Bi Reconstruction on the Si(111) Surface

Abstract

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