Atomic structure of Si(111) ( sqrt 3-bar x sqrt 3-bar)R30 degrees-B by dynamical low-energy electron diffraction

Local geometry around B atoms in B/Si(1 1 1) from polarized x-ray absorption spectroscopy

The arrangement of B atoms in a doped Si(1 1 1)-[Formula: see text]:B system was studied using a 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[Formula: see text] 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[Formula: see text]-atoms is at the surface, next to those Si atoms which form the [Formula: see text] reconstruction.

Optical second harmonic spectroscopy of boron-reconstructed Si(001)

Optical second harmonic generation (SHG) spectroscopy is used to probe Si(001) following thermal decomposition of diborane at the surface. Incorporation of boron (B) at second layer substitutional sites at H-free Si(001) intensifies and redshifts the E1 SHG spectral peak, while subsequent H termination further intensifies and blueshifts E1, in sharp contrast to the effect of bulk B doping or nonsubstitutional B. Ab initio pseudopotential and semiempirical tight binding calculations independently reproduce these unique trends, and attribute them to the surface electric field associated with charge transfer to electrically active B acceptors, and rehybridization of atomic bonds.