Positron lifetime spectroscopy and two-dimensional angular correlation of annihilation radiation have been used to investigate grown-in vacancy structures in synthetic crystalline α-SiO2, synthetic fused quartz, and in a 60-μm-thick chemical-vapor-deposited amorphous SiO2 film. For α-SiO2 a ∼300 ps lifetime component suggests trapping by either silicon monovacancies or by oxygen divacancies (or both). The vacancies are neutral and present at a concentration level of 1017/cm3. The positron bulk lifetime for α-SiO2 is estimated to be ∼238 ps in good agreement with semiempirical predictions. In the fused quartz significant positronium formation is found (80%) and the remaining positrons annihilate in voids yielding a lifetime of ∼500 ps. The amorphous SiO2 film contains a mixture of small vacancy clusters and voids and ∼30% of the positrons form positronium. Heat treatment above 950 °C results in a substantial reduction in defect concentration, but up to 1100 °C a small vacancy cluster contribution persists. The positron data indicate that positronium formation in the fused quartz and in the amorphous film takes place in the voids.

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Permission has been granted to the Libnry of The University of Manitoba to lend or sen copies of this thesislpracticum, to the National Library of Canada to microfilm this thesis/practicum and to lend or seil copies of the film, and to Dissertations Abstracts international to pubiisb an abstract of this thesis/prrcticum.The author reserves other publication rights, and neither this thesis/prrcticum nor extensive extracts from it m a y be printed or otherwisc reproduccd without the author's written permission. Abstract ABSTRACTVacancy-type defects in the four main types of diamond (Ia, Ib, IIa and IIb) were investigated using positron lifetime, Doppler broadening and optical absorption spectroscopies. In unirradiated sarnples vacancy clusters were found in al1 types, synthetic as well as natural. These clusters are situated in highly defected regions, rather than homogeneously distributed, and their concentration varies significantly from sample to sample. For synthetic Tt, diamonds vacancy clusters were investigated as a function of nitrogen content. The bulk positron lifetime for diamond is calculated to be 98 + 2 ps and the bulk Doppler S parameter is estimated to be 25% lower than that for silicon. Electron irradiation (2.3 MeV) produced neutral monovacancies in IIa diamond and the positron data correlated well, as a function of dose, with the GR1 optical zero-phonon line (the optical absorption at 740nm arise fiom neutral monovacancies in diarnond); the introduction rate was estimated to be 0.5 k 0.2 cm-'. In Ib diamond monovacancies were found to be negatively charged whereas they were neutral in IIa diamonds. The positron lifetime for monovacancies was (40 t 6)% larger than the bulk lifetime and the Doppler S parameter increased by (8 + 1)%. At-temperature Doppler measurements between 30 and 770 K indicated that irradiation-produced neutral monovacancies can convert to the negatively charged state above 400 K but this was dependent on diamond type.Isochronal annealing of irradiated Ib diarnonds showed that the complex of a substitutional nitrogen and a vacancy, formed upon annealing close to 6 0 0°c , undergoes two detectable modifications between 600 and 870 OC reaching a configuration stable to 1 170 OC . Key conclusions based on positron and optical data are in mutual accord.