The Doppler broadening of positron 2γ annihilation and the probability of positron 3γ annihilation (I3γ) was measured for SiOx (1.5 < x < 2) films with different porosities, containing paramagnetic defects (E’ and Pb), which were prepared by the radio-frequency co-sputtering of Si and SiO2 at various Ar pressures. The observed increase of I3γ with increasing Ar pressure was attributed to the increased open porosity of the film. Under a condition of constant paramagnetic defect concentration, Doppler broadening S parameter increased with increasing I3γ and open porosity of the film. This was caused by enhancement of a relative contribution from p-Ps to the 511keV 2γ annihilation peak as a

result of reduced probability of o-Ps pickoff annihilation. The relationship between the S parameter and I3γ could be affected strongly by the paramagnetic defects in the sense that film with a higher open porosity does not necessarily present a higher S parameter. A low porosity film with higher concentration Pb centers exhibited a higher S parameter than did more porous films containing lower concentration Pb centers because in the former film a larger number of positrons annihilate from p-Ps as a consequence of the Ps spin exchange caused by the paramagnetic defects.

Effects of Coexistent Pores and Paramagnetic Defects on Positron Annihilation in Silicon Oxide Thin Films. R.S.Yu, K.Ito, K.Hirata, W.Zheng, Y.Kobayashi: Journal of Applied Physics, 2003, 93[6], 3340-4