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The advantage of the high-frequency spectroscopy of electron paramagnetic resonance (EPR) for the identification of nitrogen donors and a deep compensating vanadium impurity in various crystallographic positions of the silicon-carbide crystal is shown. Measurements are performed using a new generation EPR spectrometer operating in the continuous wave and pulsed modes at frequencies of 94 and 130 GHz in a wide range of magnetic fields (–7–7 T) and temperatures (1.5–300 K). A magneto-optical closed-cycle cryogenic system (Spectormag PT), highly stable generators (94 and 130 GHz), and a cavity-free system for supplying microwave power to the sample are used.

The results of experimental studies of a wideband multimode waveguide Van Attа array constructed on the basis of multimode waveguides in the H-plane (operating when an E-polarized wave is incident) are described. The experimental results were obtained from the monostatic backscattering diagrams of an antenna array in the range of 5–18 GHz in the frequency domain. The experimental monostatic backscattering diagrams (RCS) of Van Atta antenna array shown the good agreement with the calculated one, the half-power width of radiation lobe no less ± 45°. The possibility of frequency extension of a wide-band multimode Van Atta waveguide array due to the excitation of waveguides by ultra-wideband printed dipoles is investigated. The frequency range of the array was able to expand to 6-16 GHz by the antiphase excitation of ultra-wideband printed dipoles.

As part of the first Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) key-science project, we aim to provide well-exposed (viz. deep) high-resolution spectra of representative stellar targets. These spectra will be made available in form of (electronic) atlases. The first star in this series of papers is our Sun. It also acts as a system-performance cornerstone. The deep spectra in this paper are the results of combining up to 100 consecutive exposures per wavelength setting and are compared with other solar flux atlases. Our software for the optimal data extraction and reduction of PEPSI spectra is described and verified with the solar data. Three deep solar flux spectra with a spectral resolution of up to 270,000, a continuous wavelength coverage from 383 nm to 914 nm, and a photon signal to noise ratio (S/N) of between 2,000-8,000:1 depending on wavelength are presented. Additionally, a time-series of 996 high-cadence spectra in one cross disperser is used to search for intrinsic solar modulations. The wavelength calibration based on Th-Ar exposures and simultaneous Fabry-Perot combs enables an absolute wavelength solution within 10 m/s (rms) with respect to the HARPS laser-comb solar atlas and a relative rms of 1.2 m/s for one day. For science demonstration, we redetermined the disk-average solar Li abundance to 1.09+/-0.04 dex on the basis of 3D NLTE model atmospheres. We detected disk-averaged p-mode RV oscillations with a full amplitude of 47 cm/s at 5.5 min. Comparisons with two solar FTS atlases, as well as with the HARPS solar atlas, validate the PEPSI data product. Now, PEPSI/SDI solar-flux spectra are being taken with a sampling of one deep spectrum per day, and are supposed to continue a full magnetic cycle of the Sun., in press, 13 pages, 8 figures, data available from pepsi.aip.de

The results of studies of shallow donors and deep-level color centers in bulk AlN crystals are presented. Two shallow donors (presumably oxygen located on the nitrogen site and carbon located on the aluminum site) are suggested to exhibit the DX-relaxation. Third shallow donor (presumably silicon on the Al site) shows the shallow donor behavior up to the room temperature and can be observed without light excitation at temperatures above 200 K. The values of the Bohr radius of the shallow donors are estimated. The structure of deep-level color centers (neutral nitrogen vacancy VN) in bulk AlN crystals is determined and analyzed by electron paramagnetic resonance, electron-nuclear double resonance, optical absorption and thermoluminescence induced by X-ray irradiation. Spin-dependent recombination processes in AlN crystals are studied by means of optically detected magnetic resonance.

The electron paramagnetic resonance (EPR) spectra observed in laser materials based on zinc selenide (ZnSe) crystals doped with transition elements have been analyzed and identified. It has been shown that, in addition to working impurities (Cr2+, Co2+, or Fe2+), the diffusion layer exhibits EPR spectra of accompanying impurities due to the diffusion of transition elements (chromium, cobalt, or iron) used in the preparation of active materials for quantum electronics (lasers, switches) operating in the mid-infrared range. EPR diagnostics of these impurities can be used in the development of appropriate regimes for minimizing concentrations of accompanying impurities that adversely affect the performance characteristics of laser materials. It has been found that, during the diffusion of transition metals, ions of the accompanying impurity Mn2+, which is characterized by extremely informative EPR spectra, are embedded in the crystal lattice. It has been proposed to use these ions as ideal markers to control, on the electronic level, the crystal structure of the active diffusion layer.

The Petra III synchrotron radiation source was developed based on the Petra-II 6-GeV electron accelerator (DESY). After installing the system for radiation damping, the horizontal emittance of the electron beam of Petra III decreased from 5 nm rad to 1 nm rad, which is a record parameter for this class of installations. The system of radiation damping includes 20 permanent magnet wigglers installed in two straight sections, 50 m each. The total radiation power of the wigglers reaches 800 kW. The wigglers used in the radiation damping system of Petra III were developed in collaboration with DESY (Hamburg) and fabricated by the Budker Institute of Nuclear Physics. The wiggler length is 4.04 m, the gap between the poles is 24 mm, the maximum magnetic field is B = 1.52−1.56 T, and the period is λ = 20 cm. This paper describes the design features of the permanent magnet wigglers and the methods and results of adjustment of the wiggler operating parameters.

EPR studies presented here reveal the presence of three different types of shallow donor (SD) impurities in AlN single crystals: one impurity is located at the N site (preferentially oxygen, labeled D1) and two impurities are located at the Al site (preferentially carbon and silicon, labeled D2 and D3) of the AlN lattice. We show that D1 and D2 centers exhibit a DX-like relaxation. The light-induced EPR signals of the D1 and D2 centers are characterized by slightly anisotropic g factors typical for SD in AlN but strongly different anisotropic EPR linewidths ΔB. The D3 center shows the SD behavior at the room temperature and can be observed without light excitation at the temperatures above 200 K. Combining EPR, optical absorption and thermoluminescence induced by the X-ray irradiation we establish the structure of deep level color centers in AlN - a neutral nitrogen vacancy VN. The an optical absorption band of the center is in the visible region with a maximum at ∼450 nm and the energy level at ∼0.75 eV relative to the bottom of AlN conduction band (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The electronic structure of nitrogen vacancies in specially undoped aluminum nitride single crystals has been determined and the depth of the donor level of these vacancies in the band gap has been found to be ∼75 meV by combined electron paramagnetic resonance and thermoluminescence investigations.

Electron paramagnetic resonance (EPR) and electron spin echo (ESE) at X-band and at high-frequency W-band (95 GHz) have been used to study natural diamond nanocrystals, detonation nanodiamond (ND) with a size of ∼ 4.5 nm and detonation ND after high-temperature, high-pressure sintering with a size of ∼ 8.5 nm. Isolated nitrogen centers N0 and nitrogen pairs N2 + have been detected and identified, and their structure has been unambiguously determined by means of the high frequency EPR and ESE in natural diamond nanocrystals. In detonation ND and detonation ND after sintering, isolated nitrogen centers N0 have been discovered in nanodiamond core. In addition EPR signals of multivacancy centers with spin 3/2 seem to be observed in nanodiamond core of detonation ND.

We focus on early-B type stars with helium overabundance, for which the presence of a magnetic field has not previously been reported. The measurements were carried out using high-spectral-resolution spectropolarimetric observations obtained with the High Accuracy Radial velocity Planet Searcher (HARPS) in polarimetric mode, installed at the ESO La Silla 3.6m telescope. For five He-rich stars, the longitudinal magnetic field was detected for the first time. For one target, HD58260, the presence of a longitudinal magnetic field of the order of 1.8 kG has already been reported in the literature, but the magnetic field has remained constant over tens of years. Our measurement carried out using the polarimetric spectra obtained in 2015 March indicates a slight decrease of the longitudinal magnetic field strength compared to measurements reported in previous works. A search for periodic modulation in available photometric data allowed us to confidently establish a period of 2.64119$\pm$0.00420 d in archival ASAS3 data for CPD -27$^{\circ}$ 1791. No period could be determined for the other five stars. The obtained results support the scenario that all He-rich stars are detectably magnetic and form an extension of the Ap star phenomenon to higher temperatures., Comment: Accepted as A&A Letter

We report the detection of weak mean longitudinal magnetic fields in the Herbig Ae double-lined spectroscopic binary AK Sco and in the presumed spectroscopic Herbig Ae binary HD95881 using observations with the High Accuracy Radial velocity Planet Searcher polarimeter (HARPSpol) attached to the European Southern Observatory's (ESO's) 3.6m telescope. Employing a multi-line singular value decomposition (SVD) method, we detect a mean longitudinal magnetic field =-83+-31G in the secondary component of AK Sco on one occasion. For HD95881, we measure =-93+-25G and =105+-29G at two different observing epochs. For all the detections the false alarm probability is smaller than 10^-5. For AK Sco system, we discover that accretion diagnostic Na I doublet lines and photospheric lines show intensity variations over the observing nights. The double-lined spectral appearance of HD95881 is presented here for the first time.

Electron paramagnetic resonance (EPR) at X-band (9.4 GHz) and Q-band (35 GHz) have been used to study defects in two samples of AlN monocrystals, grown by a sublimation sandwich method. These investigations reveal the presence of Fe2+ impurities in the reddish sample. The spectra of substitutional Fe2+ are highly anisotropic and could be observed even up to the room temperature. After illumination the signals showing the DX behavior were detected in the same sample. We assume these signals to arise due to the presence of the shallow donor center namely the isolated substitutional oxygen ON occupying the nitrogen position. In the second slightly amber-coloured sample EPR measurements before and after X-ray showed the presence of a deep-donor center which was assumed to be nitrogen vacancy VN. Based on thermoluminescence measurements the depth of the level was estimated to 0.45-0.5 eV.

Electron paramagnetic resonance (EPR) and electron spin echo (ESE) at X-band (9.4 GHz) and W-band (94 GHz) have been used to study defects in natural diamond nanocrystals, detonation nanodiamond (ND) with a size of  4.5 nm and detonation ND after high-pressure high-temperature (HTHP) sintering with a size of  8.5 nm. Based on identification of atomic nitrogen centers N0 and nitrogen pairs N2+ detected by means of the high frequency EPR and ESE in natural diamond nanocrystals, atomic nitrogen centers N0 have been discovered in nanodiamond core in detonation ND and detonation ND after sintering. In addition EPR signal of multi-vacancy centers with spin 3/2 seems to be observed in diamond core of detonation ND.

Electron paramagnetic resonance (EPR) and electron spin echo (ESE) at X-band and at high-frequency W-band (95 GHz) have been used to study defects in natural diamond nanocrystals, detonation nanodiamond (ND) with a size of ∼4.5 nm and detonation ND after high-temperature, high-pressure sintering with a size of ∼8.5 nm. Atomic nitrogen centers N 0 and nitrogen pairs N 2 + have been detected and identified and their structure has been unambiguously determined by means of the high frequency EPR and ESE in natural diamond nanocrystals. In detonation ND and detonation ND after sintering atomic nitrogen centers N 0 have been discovered in nanodiamond core. In addition EPR signal of multi-vacancy centers with spin 3/2 seems to be observed in diamond core of detonation ND.

High concentration of two types of P donors up to 1017 cm-3 in SiC enriched with 30Si after neutron transmutation doping (NTD) has been achieved. It was established that annealing at sufficiently low temperature of 1300oC, that is 500-600°C lower compared with annealing of NTD SiC with natural isotope composition, gives rise to the EPR signal of shallow P donors, labeled sPc1, sPc2 and sPh. The correlated changes of the EPR spectra of the three sP centres in all the experiments and the qualitative similarities with spectra of shallow N donors prove that these centres have shallow donor levels and a similar electronic structure and belong to different lattice sites. The annealing at 1700°C results in a transformation of one type of P donors (sPc1, sPc2 and sPh) into another type having low temperature EPR spectra labeled dP.

High-temperature stable defect complexes in 6H-SiC crystals created by heavy neutron irradiation and following high-temperature annealing have been discovered by electron paramagnetic resonance. After thermal annealing at 1500 °C at least five new axially symmetric centres with electron spin S = 1/2 and S = 1 were shown to arise in 6H-SiC crystals. The striking feature of all discovered centres is a strong hyperfine interaction with a great number (up to 12) of equivalent host Si (C) atoms. Two models, a four-vacancy complex VSi–3VC, and a split-interstitial antisite (C2)Si or a pair of two antisites (C2)Si–SiC are discussed. As a result of multi-defect cluster decay new triplet centres labelled as N-V have been observed in 1900 °C annealed 6H-SiC crystals which were concluded to consist of silicon vacancy and carbon substitutional nitrogen in the adjacent lattice cites oriented along the c-axis. The parameters of these centres are similar to those for the well-known N-V centre in diamond.

Two types of a new triplet centers labeled as N-V have been observed in heavily neutron irradiated (dose of 1021 cm-2) and high-temperature annealed (2000°C) 6H-SiC crystals. The centers have an axial symmetry along c-axis. Anisotropic hyperfine splitting due to the one 14N nucleus has been observed. The EPR spectra of N-V defects in the triplet state in 6H-SiC reveal strong temperature dependence. The parameters of these centers are similar to that for well-known N-V center in diamond. It seems to consist of silicon vacancy and carbon substitutional nitrogen in the adjacent lattice cites oriented along c-axis. Similar to the diamond N-V centers in SiC have been produced by neutron irradiation and high-temperature annealing of the crystals containing nitrogen. For the first shell the structure of the N-V defect in 6H-SiC is practically identical with that in diamond. The charge state of this defect seems to be +1 compare with neutral state for nitrogensilicon vacancy defect in 6H-SiC with S=1/2.

The conclusion which is drawn from the EPR line broadening and narrowing of the N shallow donor in an isotope enriched and non-enriched 4H-SiC and 6H-SiC crystals along with previous ENDOR results shows that the spin-density distribution over the C and Si nuclei differs between the 4H-SiC and 6H-SiC polytypes. The main part of the spin density in 4H-SiC is located on the Si sublattice. In contrast, in 6H-SiC the main part of the spin density is located on the C sublattice. An explanation for the difference in the electronic wave function of the N donor in 4HSiC and 6H-SiC can be found in the large difference in the band structure of two polytypes and in the position of the minima in the Brillouin zone.

The high-temperature stable defect complexes in 6H-SiC crystals created by heavy neutron irradiation and following high-temperature annealing have been discovered by EPR. After annealing at 1500°C at least five new axially symmetric centers with the electron spin S = 1/2 and S = 1 were shown to arise in 6H-SiC crystals. The striking feature of all discovered centers is a strong hyperfine interaction with a great number (up to twelve) of equivalent host Si (C) atoms. Two models, a four-vacancy complex VSi-3VC, and a split-interstitial antisite (C2)Si or a pair of two antisites (C2)Si-SiC are discussed. There is a good probability that some of new centers could be related to the famous D1 and DII centers. After annealing at 2000°C the dc1-dc4 centers disappeared and a new triplet center labeled as N-V in the form of a silicon vacancy and a nitrogen atom in neighboring carbon substitutional position has been observed. The parameters of this center are similar to that for well-known N-V center in diamond.

Five new centers with the electron spins S= 1 2 and 1 and axial symmetry along c-axis were shown by EPR to arise in SiC after heavy neutron irradiation and following high-temperature annealing at 1500°C. The striking feature of all the centers discovered was a strong hyperfine interaction with a great number of equivalent host Si (C) atoms in SiC lattice. It can be assumed that these defects have high-symmetry structure which suggests a high stability and consists in multi-vacancy clusters. In addition, antisite Si (C) atoms could be included. There is a good probability that some of the new centers could be related to famous D1 center.

The results of the first observations of paramagnetic defects in SiC crystals irradiated with gamma-ray quanta are reported. Three types of defects, designated as γ1, γ2, and γ3, were detected in irradiated 4H-SiC:Al and 6H-SiC:Al crystals using electron spin resonance (ESR) measurements. All these centers have almost the same parameters of the spin-related Hamiltonian with S=1/2 and feature an appreciable anisotropy of the g-factors. The γ1 centers are almost coaxial with the local z-axis oriented approximately along one of the directions of the Si-C bond that does not coincide with the c-axis. The γ2 and γ3 centers have a lower symmetry, although the orientation along the above bonds is clearly pronounced. The values of the largest g-factor (g z) decreases in the sequence from γ1 to γ3. The γ1 signal can be detected at temperatures of 3.5–15 K; the γ2 and γ3 signals are detectable at temperatures of 10–35 and 18–50 K, respectively. The hyperfine interaction of an unpaired electron in the γ1 center with a nucleus of the 29Si isotope is detected for certain orientations of the crystal. The γ1, γ2, and γ3 centers cease to exist at a temperature of 160°C; it is concluded that the ESR signals of these centers are related to defects in the C sublattice. It is assumed that the γ1, γ2, and γ3 centers have a common origin and are related to the low-temperature (γ1) and high-temperature (γ2 and γ3) modifications of the same center. The models of a defect in the form of either a carbon vacancy or a complex incorporating an Al impurity atom and a C atom that occupies the silicon site or interstice are discussed.

We report on the first observation of the electron paramagnetic resonance of iron impurity in SiC:Fe crystals. Iron exists in the Fe3+ (3d5) charge state with electron spin S = 5/2 and seems to occupy silicon sites in the 6H-SiC lattice. The EPR spectrum of Fe3+ in SiC shows a characteristic anisotropy of an S = 5/2 system in a strong axial crystalline field with fine structure parameter D = 0.25 cm-1. The g-factor is nearly isotropic, g = 1.99. The possibility of using iron doping to obtain semi-insulating SiC crystals is discussed.

We report the first EPR observation of rare-earth impurities in erbium doped bulk 6H-SiC crystals, grown by the sublimation sandwich-method. Two lines for axial Er 3+ centre with crystalline c -axis being the axis of the g tensor, which seem to arise from different lattice sites in 6H-SiC and three Er 3+ centres with same nearly orthorhombic symmetries, attributed to different lattice sites have been observed. A direct identification of erbium ions has been established by the presence of hyperfine interaction with 167 Er nuclei. The principal g values of the axial and orthorhombic Er 3+ centres were found. The average g values suggest that the parent cubic ground state may have γ 7 representation for both centres. Presumably, erbium substitute for silicon in a regular environment for axial centre. The orthorhombic Er 3+ seems to include another defect at carbon position along with Er 3+ ion at silicon site. The EPR spectrum of the excited state of Er 3+ in 6H-SiC seems to be observed at higher temperature. The trace amounts of the other rare-earth elements, in particular Dy 3+ , had probably been present in EPR spectra.

In this letter we report the EPR observation of the group-III deep acceptor impurities: deep B, deep Al and deep Ga centres in SiC crystals. A direct identification of the B and Ga atoms involved in the defect centre, considered as deep B and deep Ga, has been established by the presence of hyperfine interaction with 11B and 10B nuclei in isotope enriched B doped crystals and 69Ga and 71Ga nuclei in Ga doped crystals. In contrast to the results for the group-III shallow acceptor impurities in SiC, the observed qualitative behaviour for Al and Ga deep level impurities is the same as that for B. No effective-mass-like behaviour was observed for deep group-III acceptors. Deep centres were shown from EPR spectra to have symmetry nearly axial around the hexagonal axis of the crystal. Evidence of strong thermally activated dynamic effects having common features for the EPR spectra of all deep centres have been observed. The structural model for deep centre as an impurity-vacancy pair are presented. For shallow B acceptor off-centre position of B which is induced by chemical rebonding was suggested and as a result no effective-mass-like behaviour was observed. It was indicated from ODMR of deep Al acceptors that deep Al level is about 0.1 eV shallower as compared to deep B.

The necessity of extending the useful spectrum of synchrotron radiation at higher energies (> 10 keV) for X‐Ray Diffraction applications was the reason for developing and constructing a novel superconducting insertion device the Elettra storage ring. The superconducting wiggler with 45 full poles and a field strength of 3.5 T, 16.5 mm magnetic gap and a period of 64 mm has been developed and produced by the Budker Institute of Nuclear Physics SB RAS. This article describes some technical properties and characteristics of the wiggler as well as the results of the wiggler tests.

The phosphorus related defects in n-type 6H-SiC monocrystals doped by neutron transmutation have been studied by electron paramagnetic resonance (EPR) spectroscopy. After thermal annealing at 1900°C two sets of three phosphorous related EPR spectra are observed, which are attributed to the isolated shallow P donor on the two quasicubic (c1,c2) and the hexagonal (h) sites as well as to a deep P center on the c1, c2, h sites. The deep P center is tentatively attributed to the P S i -carbon vacancy complex. Our results show in agreement with theoretical predictions that the previous suggestions that the two types of centers are the ground and excited states of the isolated P donor can be ruled out. The donor-monovacancy complexes are characterized by an exceptional thermal stability.

Electron paramagnetic resonance (EPR) spectra of rare-earth Dy3+ and Ce3+ ions in lead thiogallate PbGa2S4 single crystals were discovered and investigated. EPR spectra were studied in X-band in the temperature range 4–30 K. Parameters of spin Hamiltonian of EPR spectra of Dy3+ and Ce3+ ions in PbGa2S4 single crystals were calculated. It was set that dysprosium and cerium ions replace lead ions in crystal lattice. Also we carried out a diagnosis of ZnSe crystals doped with different rare-earth and transition metal ions. It was shown that due to diffusion of transition elements of Cr3+, Co2+ or Fe3+ along with the working admixture in the diffusion layer the EPR spectra of related admixtures are detected. The EPR diagnosis of these admixtures can be used in the development of modes, allowing minimizing the concentration of related admixtures, worsening the performance of laser materials. It was found that diffusion of Cr, Co and Fe transition metal ions leads to admixture of Mn ions. The EPR signals of Mn and Co are proposed as the ideal markers to control the crystal structure of the diffusion active layer.

While monitoring the flare star EV Lac with high time resolution using the Space Astrophysical Station ASTRON, a rather strong flare was recorded. During this event, flare emissions were detected in the C IV (λ1550 Å) UV line, in the narrow band continuum at λ2434 Å (28 Å bandwidth) and in the wide wavelength range from 1700 Å to 6500 Å, all emission enhancements taking place within 10 s. About 50 s after the flare start, a fast and very powerful burst of the C IV line took place.

Photoelectric observations of flares on two low-active red dwarfs (Gliese 171.2A and CM Dra) are reported.