It was noted that adsorption of B induced a (√3 x √3 )R30° reconstruction on Si(111). By combining scanning tunnelling microscope topographs and spectra with first-principles calculations, it was possible to monitor the various stages of B incorporation into the Si surface, and the corresponding changes in the surface electronic states. It was found that the thermodynamically stable configuration consisted of a B substitutional atom directly below a Si adatom at a T4 site. The stability of this configuration was due to the relief of sub-surface strain by the short B-Si bonds and the passivation of the surface obtained through charge transfer from the Si adatom to the substitutional B.

Adsorption of Boron on Si(111) - Its Effect on Surface Electronic States and Reconstruction. I.W.Lyo, E.Kaxiras, P.Avouris: Physical Review Letters, 1989, 63, 1261-4