Local geometry around B atoms in B/Si(111) from polarized x-ray absorption spectroscopy

The arrangement of B~atoms in a doped Si(111)-$(\sqrt{3}\times\sqrt{3})R30^{\circ}$:B system was studied using near-edge x-ray absorption fine structure (NEXAFS). Boron atoms were deposited via segregation from the bulk by flashing the sample repeatedly. The positions of B~atoms are determined by comparing measured polarized (angle-dependent) NEXAFS spectra with spectra calculated for various structural models based on ab-initio total energy calculations. It is found that most of boron atoms are located in sub-surface L$_{1}^{c}$ positions, beneath a Si atom. However, depending on the preparation method a significant portion of B~atoms may be located elsewhere. A possible location of these non-L$_{1}^{c}$-atoms is at the surface, next to those Si atoms which form the $(\sqrt{3}\times\sqrt{3})R30^{\circ}$ reconstruction.