Characterization of E{sup '}{sub {delta}} and triplet point defects in oxygen-deficient amorphous silicon dioxide
- Department of Physical and Astronomical Sciences, University of Palermo, Via Archirafi 36, I-90123 Palermo (Italy)
We report an experimental study by electron paramagnetic resonance (EPR) of {gamma}-ray irradiation induced point defects in oxygen deficient amorphous SiO{sub 2} materials. We have found that three intrinsic (E{sup '}{sub {gamma}}, E{sup '}{sub {delta}}, and triplet) and one extrinsic ([AlO{sub 4}]{sup 0}) paramagnetic centers are induced. All the paramagnetic defects but E{sup '}{sub {gamma}} center are found to reach a concentration limit value for doses above 10{sup 3} kGy, suggesting a generation process from precursors. Isochronal thermal treatments of a sample irradiated at 10{sup 3} kGy have shown that for T{>=}500 K the concentrations of E{sup '}{sub {gamma}} and E{sup '}{sub {delta}} centers increase concomitantly to the decrease of [AlO{sub 4}]{sup 0}. This occurrence speaks for a hole transfer process from [AlO{sub 4}]{sup 0} centers to diamagnetic precursors of E{sup '} centers proving the positive charge state of the thermally induced E{sup '}{sub {gamma}} and E{sup '}{sub {delta}} centers and giving insight on the origin of E{sup '}{sub {gamma}} from an oxygen vacancy. A comparative study of the E{sup '}{sub {delta}} center and of the 10 mT doublet EPR signals on three distinct materials subjected to isochronal and isothermal treatments has shown a quite general linear correlation between these two EPR signals. This result confirms the attribution of the 10 mT doublet to the hyperfine structure of the E{sup '}{sub {delta}} center, originating from the interaction of the unpaired electron with a nucleus of {sup 29}Si (I=1/2). Analogies between the microwave saturation properties of E{sup '}{sub {gamma}} and E{sup '}{sub {delta}} centers and between those of their hyperfine structures are found and suggest that the unpaired electron wave function involves similar Si sp{sup 3} hybrid orbitals; specifically, for the E{sup '}{sub {delta}} the unpaired electron is supposed to be delocalized over four such orbitals of four equivalent Si atoms. Information on the structural model of the triplet center are also obtained indicating that it could consist of the same microscopic structure as the E{sup '}{sub {delta}} but for a doubly ionized state.
- OSTI ID:
- 20787854
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 73, Issue 4; Other Information: DOI: 10.1103/PhysRevB.73.045208; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AMORPHOUS STATE
ATOMS
CHARGE STATES
CORRELATIONS
CRYSTALS
ELECTRON SPIN RESONANCE
ELECTRONS
GAMMA RADIATION
HEAT TREATMENTS
HOLES
HYPERFINE STRUCTURE
IRRADIATION
MICROWAVE RADIATION
OXYGEN
PARAMAGNETISM
POSITRONS
SILICON 29
SILICON OXIDES
STRUCTURAL MODELS
TRIPLETS
VACANCIES
WAVE FUNCTIONS