We report an experimental study by electron paramagnetic resonance EPR of -ray irradiation inducedpoint defects in oxygen deficient amorphous SiO2 materials. We have found that three intrinsic E , E , andtriplet and one extrinsic AlO4 0 paramagnetic centers are induced. All the paramagnetic defects but E center are found to reach a concentration limit value for doses above 103 kGy, suggesting a generation processfrom precursors. Isochronal thermal treatments of a sample irradiated at 103 kGy have shown that for T 500 K the concentrations of E and E centers increase concomitantly to the decrease of AlO4 0. Thisoccurrence speaks for a hole transfer process from AlO4 0 centers to diamagnetic precursors of E centersproving the positive charge state of the thermally induced E and E centers and giving insight on the originof E from an oxygen vacancy. A comparative study of the E center and of the 10 mT doublet EPR signalson three distinct materials subjected to isochronal and isothermal treatments has shown a quite general linearcorrelation between these two EPR signals. This result confirms the attribution of the 10 mT doublet to thehyperfine structure of the E center, originating from the interaction of the unpaired electron with a nucleus of29Si I=1/2 . Analogies between the microwave saturation properties of E and E centers and between thoseof their hyperfine structures are found and suggest that the unpaired electron wave function involves similar Sisp3 hybrid orbitals; specifically, for the E the unpaired electron is supposed to be delocalized over four suchorbitals of four equivalent Si atoms. Information on the structural model of the triplet center are also obtainedindicating that it could consist of the same microscopic structure as the E but for a doubly ionized state.
|Numero di pagine||8|
|Rivista||PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS|
|Stato di pubblicazione||Published - 2006|
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