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Using the atom probe tomography, transmission electron microscopy, and ab initio calculations, we investigate the three-dimensional distributions of oxygen atoms segregating at the typical large-angle grain boundaries (GBs) (Σ3{111}, Σ9{221}, Σ9{114}, Σ9{111}/{115}, and Σ27{552}) in Czochralski-grown silicon ingots. Oxygen atoms with a covalent radius that is larger than half of the silicon's radius would segregate at bond-centered positions under tensile stresses above about 2 GPa, so as to attain a more stable bonding network by reducing the local stresses. The number of oxygen atoms segregating in a unit GB area NGB (in atoms/nm2) is hypothesized to be proportional to both the number of the tensilely-stressed positions in a unit boundary area nbc and the average concentration of oxygen atoms around the boundary [Oi] (in at. %) with NGB∼50nbc[Oi]. This indicates that the probability of oxygen atoms at the segregation positions would be, on average, fifty times larger than in bond-centered positions in defect-free regions.

Energy spectra of positron annihilation radiation were measured in polymer blends of polyethylene and ethylene vinyl acetate copolymer ͑E/VA͒ by means of the coincidence Doppler broadening technique. Positron annihilation with the core electrons of oxygen was appreciably increased by the addition of small amounts of E/VA to polyethylene and was detected with a sensitivity one order of magnitude higher than would be expected from the number density of the oxygen atoms in the polymer blends. This clearly shows that the positron is sensitively trapped by the polar acetate group of E/VA and demonstrates the usefulness of positrons as a sensitive chemical probe for polar structures in a nonpolar polymer matrix with high positron mobility.

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