The improved compared to a rectangular TE(102 )cavity geometry of a dielectric resonator (DR) suitable for studying thin films and coatings has been calculated and experimentally verified. It is shown that electron paramagnetic resonance (EPR) signal of SiOx films can be enhanced by using as the DR of two rectangular parallelepipeds fabricated from BaTi4O9 + 8.5% ZnO ceramics (epsilon=36) with dimension of 5.64x5.5 x 5.9 mm(3 )and a gap of up to 0.5 mm between them. Located inside a standard rectangular metal TE(102 )cavity of the X-band EPR spectrometer, the DR increases the filling factor by 5-12 times depending on the size of a sample studied. The experimental use of the DR allows to increase the EPR signal of the 950 nm SiOx thin film by a factor of approximately 4.

Addition functionalization after high-pressure oxidation of 2D macroporous silicon structures is evaluated. X-ray diffractometry indicates formation of orthorhombic SiO2 phase on macroporous silicon at oxide thickness of 800-1200 nm due to cylindrical symmetry of macropores and high thermal expansion coefficient of SiO2. Pb center concentration grows with the splitting energy of LO-and TO-phonons and SiO2 thickness in oxidized macroporous silicon structures. This increase EPR signal amplitude and GHz radiation absorption and is promising for development of high-frequency devices and electronically controlled elements. (C) 2017 Elsevier B.V. All rights reserved.

This work presents theoretical studying the neutral divacancy, i.e., the Ky5 center that is one of the dominant defects in 3C-SiC bulk crystals subjected to relatively high dose of neutron irradiation. Being the paramagnetic center, the extended defect Ky5 shows the value of the zero field splitting (ZFS) in the electron paramagnetic resonance (EPR) signal D = 443.10(-4)cm(-1) and 454.10(-4)cm(-1) in two modifications. To understand the ZFS value, relativistic ab initio calculation has been carried out for obtaining the electron structure of 3C-SiC crystal containing the defect Ky5. Using the WIEN program package, the self-consisting values of the electron density rho and controlling rho potential V have been found. Based on the obtained values rho and V, the contributions in ZFS from dipole-dipole and spin-orbit interactions have been found. It has been shown that the main contribution stems from the dipole-dipole interaction. Spin-orbit interaction gives a negligible contribution to ZFS. Due to the relativistic approach, spin-up and spin-down values of the electron density have been obtained, which permits to calculate the hyperfine fields at the nuclei in environment of the divacancy in 3C-SiC.

We demonstrate availability of gas detonation deposition spraying (GDS) to obtain silicon layers that can be used for production of solar cells. Silicon powder remaining as secondary raw material of silicon and/or silicon production is used during GDS. To study defects and structural perfection of initial powders and obtained layers, electron paramagnetic resonance (EPR) and Raman spectroscopy are used. It is shown that one part of EPR spectra displays resonances originating from different nearest-neighbor configurations of silicon dangling bonds, whereas an increase of the total number of paramagnetic defects in GDS silicon layer is related to the rise of conduction electrons or electrons filled band tail states. Thermal annealing of layers in hydrogen ambience further reduces the number of silicon dangling bonds owing to their passivation. Based on the results of X-ray diffraction, EPR and Raman spectroscopy it is assumed that the GDS Si layers are composed of randomly oriented and partially oxidized monocrystalline silicon grains. It is found that optical and photoelectric properties of the layers obtained indicate a possibility to apply them for solar cells production.

A careful study of neutron-irradiated cubic SiC crystals (3C-SiC < n >) has been performed using electron paramagnetic resonance (EPR) in the course of their thermal annealing within the 200 ... 1100 degrees C temperature range. Several inherent temperatures have been found for annealing and transformations of primary defects in 3C-SiC < n > among which there are isolated negatively charged silicon vacancy V-Si(-) neutral divacancy (V-si-V-C)(0), negatively charged carbon vacancy-antisite pair (V-C-C-Si)(-) and neutral carbon < 100 > split interstitial (CC)(C)(0). It has been shown that transformation of V-si(-) into (V-C-C-Si)(-) complex is among the mechanisms of silicon vacancy annealing. As it has been established on the basis of the observed hyperfine structure, the secondary T6 center is characterized by the fourfold silicon coordination and assigned to the spin S = 3/2 carbon vacancy-related pair defect. The symmetry reduction of the (V-C-V-Si)(0) center is attributed to local rearrangements in the neighborhood of divacancy, and its intensity variations are assigned to changes of the Fermi-level position. Two defects with similar symmetry and close values of zero-field splitting constants D, which concentrations increase by a factor` of ten after annealing at 900 degrees C, are tentatively attributed to the < 100 > split interstitial (CC)(C)(0) and (NC)(C)(0) pairs.

The results of electron paramagnetic resonance (EPR) study of obliquely deposited porous SiOx films before and after thermal annealing in vacuum at 950°C are presented. The low intensity slightly asymmetrical and featureless EPR line with a g-value of 2.0044 and a linewidth of 0.77mT has been detected in as-sputtered films and attributed to dangling bonds of silicon atoms in amorphous SiOx domains with x=0.8. Successive annealing results in decreasing this line and the appearance of an intense EPR line with g=2.0025, linewidth of 0.11mT and a hyperfine doublet with 1.6mT splitting. According to the parameters this spectrum has been attributed to the EX center, a hole delocalized over four non-bridging oxygen atoms grouped around a Si vacancy in SiO2. The impact of chemical treatment before annealing and duration of anneals on the defect system is discussed.

The results of correlated electron paramagnetic resonance (EPR) and photoluminescence (PL) study of obliquely deposited porous SiO x films after step-by-step 15 min annealing within 105 min in vacuum at 950°C are presented. The low intensity symmetrical and featureless EPR line with a g-value g=2.0044 and a linewidth of 0.77 mT has been detected in as-sputtered films and attributed to dangling bonds ( DB ) of silicon atoms in amorphous SiO x domains with x =0.8. Successive annealing results in decreasing this line and the appearance of an intense EPR line with g=2.0025, linewidth of 0.11 mT and a hyperfine doublet with 1.6 mT splitting. According to the parameters this spectrum has been attributed to the EX center, a hole delocalized over four non-bridging oxygen atoms grouped around a Si vacancy in SiO 2 . The impact of chemical treatment before annealing and duration of anneals on the defect system, and a correlation of the PL intensity with decreasing of the DB EPR signal are discussed.

EPR spectroscopy has been used to characterize neutron-irradiated cubic SiC samples after thermal annealing in the 200-1100 O C 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.

Photoluminescence (PL) spectroscopy has been used to characterize neutron-irradiated cubic silicon carbide crystals. The effects of thermal annealing (600-1100 O C) on the PL bands have been studied. Several PL bands consisting of a sharp line and its phonon replicas have been observed in the 9-80 K temperature range. Certain of them like the D 1 spectrum doublet with 1.975 eV and 1.977 eV zero-phonon lines (ZPL) at 9 K and the L2 spectrum with ZPL at 1.121 eV were reported previously for ion-implanted and electron irradiated 3C-SiC crystals, respectively. Besides, some new bands with ZPL at 2.027, 1.594, 0.989 and 0.844 eV and a broad band at 1.360 eV have been found. A correlation of PL and EPR spectra intensities of these neutron-irradiated and annealed cubic SiC crystals is briefly discussed.

The behavior of a hydrogen impurity in the course of crystallization of thin silicon films doped with tin (a-SiSn films) has been studied. It is found that the band located at about 2000–2200 cm^−1 and corresponding to the IR absorption at silicon–hydrogen bonds is absent from the spectra of as-deposited (at a temperature of 300 ◦C) a-SiSn films with Sn contents within the interval of 1–10 at.%. In undoped thin silicon films (a-Si films), the hydrogen content diminishes below the sensitivity threshold of the measurement technique only after the annealing of the specimens at 700 ◦C. The absence of hydrogen in a-SiSn films is in good agreement with the results of EPR studies and the results of Raman scattering studies of structural transformations in thermally treated films. It is shown that the formation of crystalline phases in a-SiSn occurs at lower temperatures as compared to those in a-Si, with a correlation taking place between the crystallization temperature for Si clusters and the concentration of the tin impurity. Taking into account that tin reduces the temperature of the hydrogen effusion from the film volume and, accordingly, stimulates the ordering in the specimen structure, it is possible to consider that hydrogen impurity takes part in the processes that result in a decrease of the crystallization temperature for a-SiSn.

The effect of HF and H 2 O 2 vapor treatment on the spectral composition and intensity of photoluminescence (PL) in porous oblique deposited nc-Si-SiO x structures have been studied using FTIR, electron-spin resonance (EPR) and PL measurements.As a result of HF vapor treatment, considerable PL intensity growth and blueshift of PL peak position are observed.It is suggested that the evolution of the PL spectra in HF vapor-treated samples can be attributed to selective-etching-induced decrease in Si nanoparticle dimensions and to passivation of Si dangling bonds (that are nonradiative recombination trap states) by hydrogen and oxygen.Additional treatment in H 2 O 2 vapor results in additional nc-Si surface oxidation and reduction of nc-Si size.The possibility to control the PL characteristics (peak position and intensity) of the porous nc-Si-SiO x structures in a wide range by above treatments is shown..

The article presents the results of porous SiC (PSiC) characterizations using x-ray diffraction (XRD) and electron paramagnetic resonance (EPR) techniques. Two types of PSiC samples, electrochemically as-etched and electrochemically etched and reactive ion treated, have been investigated. The XRD study shows that original SiC wafers and porous SiC layers have mainly the 6H-SiC crystal type with inclusions of 4H-SiC and 15R-SiC polytypes. With increasing porosity and porous layer thickness a new XRD band appears and grows that is assigned to the phase of amorphous graphite at the PSiC surface. The EPR spectra of PSiC layers measured at room temperature reveal low intensity signal in the g-value region of g=2.0027 and a peak-to-peak width of about 0.24–0.42 mT. The intensity of this signal increases simultaneously with the rise of PSiC thickness. The EPR study shows that the carbon dangling bond centers at and near the 6H-SiC/SiO2 interface are the dominant defects for electrochemically etched porous 6H-SiC samples.

After fast neutron irradiation with a dose of 1019cm−2 a new defect, labeled Ky5, has been revealed in the EPR spectra in addition to the dominant spectrum of the negatively charged silicon vacancy, the T1 center. Angular variation of the Ky5 spectrum indicates its origin from a spin S=1 defect. This spectrum can be detected in darkness in the whole temperature range 4.2–295K with practically unchanged parameters confirming a triplet ground state of the Ky5 center. Its spin Hamiltonian parameters are isotropic g=2.003 and axially symmetric D tensor aligned along 〈111〉 crystal directions, D=443×10−4cm−1. The angular dependence of the hyperfine structure could not be analyzed for the Ky5 center due to its relatively broad EPR linewidths, about 0.67mT. Three times narrower lines are observed at about half-field range representing forbidden ΔMS=2 EPR transitions where hyperfine splittings are found for some crystal directions. Based on the symmetry and closeness with spin Hamiltonian parameters in 4H-SiC and 6H-SiC the Ky5 center has been tentatively assigned to the neutral divacancy in cubic SiC.

Sapphire (α-Al2O3) single crystals grown using the Verneuil and Kyropoulos methods have been analyzed using electron paramagnetic resonance and γ-ray spectroscopy with 12-MeV bremsstrahlung excitation. It is established that uncontrolled impurities in the final sapphire single crystals grown by the Kyropoulos method in molybdenum-tungsten crucibles are supplied both from the initial materials and from the furnace and crucible materials

Lithium niobate crystals doped with neodymium and ytterbium were studied with the help of the electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and optical absorption. Tremendous narrowing of magnetic resonance lines in nearly stoichiometric samples in comparison with congruent ones allowed us to distinguish four non-equivalent centers (NEC) of Nd3+ and five NEC of Yb3+, as well as line splitting caused by hyperfine interaction of neodymium electrons with nuclear spins of magnetic isotopes Nd-143, Nd-145, Yb-171 and Yb-173. It was shown that some of the centers has axial C3 symmetry, whereas all others have lowest Cl symmetry due to presence of intrinsic defects or/and charge compensation defects in the near neighborhood of Nd3+ and Yb3+. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Ky1, Ky2, and Ky3 centers are the dominant defects produced in the electron-irradiated p-type 6H-SiC crystals. The electron paramagnetic resonance study of these defects has been performed in the temperature range of 4.2-300 K at X, K, and Q bands. The centers are characterized by the fourfold silicon coordination established on a basis of the observed hyperfine structure. At low temperatures both Ky1 and Ky2 defects reveal the C-S symmetry that only slightly deviates from the D-2d one. At high temperatures, the thermally activated reorientation from one Jahn-Teller distortion to the others causes the averaging of the Ky1 and Ky2 spectra in such a manner that their spin-Hamiltonians correspond to the axial symmetry. The Ky3 center has axial symmetry in all the temperature range under investigation. Its hyperfine parameters for the first-shell silicon atoms are substantially different from those determined for the Ky1 and Ky2.centers. Based on the density functional theory, the calculations of the electronic structure of a number of fourfold silicon coordinated defects have been carried out for the unambiguous identification of the observed defects through the comparison of experimentally determined and calculated hyperfine parameters. The present study proves an assignment of the Ky1, Ky2, and Ky3 centers to the positively charged carbon vacancy located in two quasicubic and hexagonal sites of the 6H-SiC lattice, respectively. The features of the V-c(+) defect related to the multivalley character of its potential energy surface are also discussed. It is shown that this defect can be localized in the minima of different symmetry depending on the occupied lattice site, and these minima are experimentally distinguishable by the values of hyperfine parameters.

Electron paramagnetic resonance (EPR) and photoluminescence (PL) have been used to study SiO2 films grown by thermal oxidation of silicon substrates and possessing either a homogeneous distribution or that close to a Gaussian one of implanted Ge atoms. The E'(gamma) centers connected with oxygen vacancies in SiO2 and the defects induced by replacing Si atoms in the matrix sites by Ge ones have been identified as dominant paramagnetic defects. Among the latter, the Ge E ' and Ge(2) centers, as well as the germanium peroxy radical Ge PR, have been recognized. The fact that the concentration of defects in specimens with a homogeneous distribution of Ge atoms was an order of magnitude lower than that in specimens with a Gaussian distribution has been explained by a dynamic annealing of defects during the multiple implantation. The revealed correlation between the intensity variations of EPR spectra and PL bands peaked at 1.94, 2.00, and 2.20 eV, which took place at annealing, testifies to that those bands are of the defect nature. At the same time, the PL band with a maximum at 2.32 eV, which appeared after annealing at 900 degrees C, has been connected with the formation of Ge nanocrystallites in SiO2.

Nanocrystalline silicon films formed using laser ablation of silicon targets were studied using electron spin resonance. The measurements were performed in the X band with modulation of the magnetic field at a frequency of ∼100 kHz at temperatures of 300 and 77 K. Two types of spectra were observed. The first type of spectra is related to the high concentration of dangling silicon bonds in Si nanocrystals and SiOx sheaths of nanocrystals and are inherent in nanocrystalline silicon (nc-Si) films that do not exhibit photoluminescence in the visible region of the spectrum. The second type of spectra is related to the presence of E′ centers, nonbridging oxygen hole centers (NBOHC), and peroxide radicals and is characteristic of films with photoluminescence in the visible region of the spectrum, which indicates that high-barrier SiO2 layers exist in these films. An increase in the photoluminescence intensity and a decrease in the signal of electron spin resonance were observed in porous nc-Si films exposed to atmospheric air for a long time.

A brief review of original ele tron paramagneti resonan e (EPR) and ele tron{nu lear double resonan e (ENDOR) studies on some sili on-based stru tures with nano rystallites is presented. The Pb enter in high-temperature annealed porous sili on has been investigated with ENDOR. High sensetivity of the ENDOR te hnique to hydrogen presen e has been found. In Si-, Ge- and C-implanted layers of SiO2 and spark-pro essed sili on the distin t sili on- and oxygen-va an y asso iated defe ts have been identi(cid:12)ed with EPR. The origin of the defe ts in spark-prose ed Si is dis ussed in detail. The resumblen e and distin tion of the defe ts in sili on-based matri es with nano rystallites illustrate a variety of stru tural transformations there. The role of paramagneti defe ts in photolumines en e is brie(cid:13)y dis ussed.