EPR Study Of Defects Research Articles

An EPR Study of Defects in Neutron-Irradiated Cubic SiC Crystals

EPR spectroscopy has been used to characterize neutron-irradiated cubic SiC samples after thermal annealing in the 200-1100OC temperature range. Three new paramagnetic defects named Ky6, Ky7 and Ky8 have been revealed. Based on the present results, these defects have been tentatively attributed to the negatively charged carbon vacancy-carbon antisite pair, negatively charged divacancy and neutral carbon <100> split interstitial, respectively. Furthermore, the finding of practically isotropic hyperfine splitting for EPR lines of the T6 center confirms its assignment as a carbon vacancy-interstitial pair.

EPR study of defects in as-received, γ-irradiated and annealed monoclinic HfO 2 powder

Electron paramagnetic resonance reveals the presence of several paramagnetic centres in monoclinic HfO 2 powders. Three labeled H1, H2, H3 have g // = 1.940 ± 0.003, g ⊥ = 1.970 ± 0.001 for H1, g xx = 2.003 ± 0.003, g yy = 2.000 ± 0.003 and g zz = 1.994 ± 0.001 for H2 and g xx = 2.014 ± 0.002, g yy = 2.013 ± 0.003 and g zz = 2.006 ± 0.002 for H3. Irradiation with γ rays causes the population of H2 and H3 to initially rise and then level off; H1 is unaffected by irradiation. H2 and H3 begin to anneal out at or below 100 °C in air whereas the population of H1 increases at about 400 °C. Models are suggested for these centres.

Flight to Mars and radiation defects in Li2B4O7 and KTiOPO4 crystals

AbstractSolar, space, laser and nuclear reactor radiations lead to the appearance of defects in complex oxides and to inevitable performance degradation of devices based on these materials. Since many radiation defects are paramagnetic ones, the electron paramagnetic resonance, EPR is one of the most suitable method for their study. Results of optical and EPR study of defects in as grown and irradiated Li2B4O7 and KTiOPO4 crystals are presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Luminescence and EPR studies of defects in Si-SiO2films

Co-sputtered Si-rich SiO 2 films annealed at 1150 °C are studied by photoluminescence and EPR methods. It is found that the emission spectrum of as-prepared samples contains one broad infrared band. It is shown that one-year aging in ambient air and low-temperature annealing in an oxygen atmosphere leads to an increase in the infrared band intensity and the appearance of additional bands with maxima at 1.7 eV, 2.06 eV and 2.3 eV while annealing in a hydrogen atmosphere results in the decrease of the 1.7 eV and 2.06 eV band intensities. A correlation between the 1.7-eV band intensity and the EPR signal from EX-centers is found to exist. The decrease of crystallite sizes results in a high-energy shift of the infrared band while the peak positions of the other ones (at 1.7 eV, 2.06 eV and 2.3 eV) do not change. The infrared band is ascribed to recombination in Si crystallites while the others are attributed to silicon oxide defects. the 1.7-eV and 2.06-eV bands being due to oxygen-excess defects such as EX-center and NBOHC.

EPR Studies of defects in silicon

AbstractElectron and neutron irradiated, plastically deformed silicon has been studied by EPR. Irradiation resulted in a strong decrease of the EPR spectra produced by the deformation and in the appearance of a new EPR center at dislocations. Thermal annealing lead to a reestablishment of the formerly present dislocation spectra. As most probable explanation is proposed a change of the dislocation strain field by irradiation induced point defect iclusters. – EPR investigations of iron in boron doped Si demonstrated the pairing of all nterstitial iron in FeB pairs during room temperature storage. Thermal treatment at temperatures higher than 100°C lead to the reappearance of Fe. Therefore the time limiting factor for the annealing of FeB pairs should be the precipitation of interstitial iron.

EPR techniques for studying defects in silicon

Due to long spin-lattice relaxation times and low defect concentrations, the EPR study of defects in irradiated silicon requires special experimental capabilities. The superheterodyne spectrometer described in this paper, which has been used in numerous defect studies, can detect 1010 spins/Oe linewidth. This spectrometer employs superstabilized, phase-locked klystrons, can be tuned to either the absorption or the dispersion mode, utilizes phase-sensitive detection, and can operate at either X or K band. The microwave probe and cryogenic system allow us to produce defects in situ at low temperatures and to probe these defects with light, stress, and annealing. For these measurements the cavity and sample can be stabilized to ±0.01 K between 4 and 300 K.

EPR studies of defects in electron-irradiated silicon: A triplet state of vacancy-oxygen complexes

Three new EPR spectra ($\mathrm{Si}\ensuremath{-}A14,\ensuremath{-}A15, \mathrm{and} \ensuremath{-}A16$) and two previously known spectra ($\mathrm{S}\mathrm{i}\ensuremath{-}P2 \mathrm{and} \ensuremath{-}P4$) are observed for the first time in electron-irradiated silicon. The microscopic defect models are established as multivacancy-oxygen complexes with the oxygen(s) in Si-O-Si structure inside the 110g vacancy chain: a (divacancy plus oxygen) for $\mathrm{S}\mathrm{i}\ensuremath{-}A14$, a (divacancy plus two oxygen) for $\mathrm{S}\mathrm{i}\ensuremath{-}P2$, a (trivacancy plus oxygen) for $\mathrm{S}\mathrm{i}\ensuremath{-}P4$, a (trivacancy plus two oxygen) for $\mathrm{S}\mathrm{i}\ensuremath{-}P5$, and a (trivacancy plus three oxygen) for $\mathrm{S}\mathrm{i}\ensuremath{-}A15$. The number of vacancies in the 110g chain is determined from the zero-field fine structure and the number of oxygens from the evolutionary kinetics, with the $g$ tensor, $^{29}\mathrm{Si}$ hyperfine structure, and stress response providing strong supportive evidence. It is emphasized that some of these oxygen-dependent defects play an important role as trapping centers for other point defects.