Geometric and electronic structure of Sb on Si(111) by scanning tunneling microscopy

Scanning tunneling microscopy and spectroscopy (STS) are used to investigate the Si(111)-Sb surface. At an Sb coverage of a few percent of a monolayer (ML), Sb substitutes Si adatoms in the 7×{}7 reconstruction. At about 1/3 ML, the 7×{}7, ``disordered 7×{}7,'' and {}3 ×{} {}3- R30^∘{} reconstructions are observed. This sub-ML {}3 ×{} {}3 reconstruction is a simple adatom phase. The T4 site is identified as the chemical bonding site of Sb adatoms in these low-coverage reconstructions. Spatially resolved STS shows the complex nature of the electronic structure of Si(111)7×{}7-Sb as compared to the clean Si surface. At the saturation coverage of 1 ML, domains of 1×{}1, 2×{}1, and a different {}3 ×{} {}3 reconstruction are observed, and structure models are proposed.