  The preferred location of boron and phosphorus in oxidized free-standing Si
nanoparticles was investigated using a first-principles density functional
approach. The calculated formation energies indicate that P should segregate to
the silicon core, whereas B is equally stable in the Si and SiO_2 regions. Our
models thus suggest that, in contrast with nanocrystals with H-terminated
surfaces, the efficiency of phosphorus incorporation in oxidized Si
nanoparticles can be improved by thermal annealing.
