  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.
