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Nanocrystalline iridium coatings on hafnium carbide and tantalum carbide substrates are prepared by chemical vapor deposition (MOCVD) at 600°С. Subsequent high-temperature treatment at 1100°С gives rise to chemical reactions between iridium and hafnium carbide or tantalum carbide to yield nanosized substitutional intermetallic solid solutions MIr3 – x and evolve free carbon. The occurrence of intermetallic interaction is proved by X-ray photoelectron (XPS) spectroscopy.

A scanning optical quantum magnetometer with submicron spatial resolution is proposed that is based on the phenomenon of hole burning in the signal of optically detected magnetic resonance (ODMR) on atomic-sized color centers in silicon carbide crystals under conditions of spin level saturation by means of additional high-frequency resonance pumping. An increase in the sensitivity is achieved due to narrowing of the ODMR line and increasing slope of the dependence of signal frequency on the magnetic field.

Volatile iridium(I) complexes [Ir(cod)Cpx] (Cpx = pentamethylcyclopentadienyl Cp*, ethylcyclopentadienyl CpEt, cod = 1,5-cyclooctadiene) are synthesized and characterized by IR and NMR spectroscopy. The [Ir(cod)Cp*] complex is a solid and the [Ir(cod)CpEt] complex is a liquid (SATP). The XRD method is used to determine the structure of the [Ir(cod)Cp*] complex: chemical formula C18H27Ir, space group P21/c, a = 8,4418(2) A, b = 9,4764(3) A, c = 19.2682(5) A, β = 96.128(1) °, V = 1532.61(7) A3, Z = 4, d calc = 1.888 g/cm3, μ = 8.697 mm–1. The cyclopentadienyl ligand is η5-type coordinated; 1,5-cyclooctadiene have a cis-cis conformation and is η4-type coordinated. The thermal properties of the complexes are studied by thermogravimetry.

A novel complex [Ag(ptac)]∞ (1) (ptac = tBuC(O)CHC(O)CF3) has been prepared by interaction of Ag2O and Hptac, its structure being elucidated by single crystal X-ray diffraction. The complex has a chain polymeric structure originating from tetradentate-μ-bridging coordination of the ptac ligands and interactions Ag–Cγ between adjacent {Ag(ptac)} fragments. The coordination environment of the silver atom is a distorted square pyramid. The distances Ag–O are 2.362(10)-2.600(10) A; Ag–Cγ–2.32(2) A and 2.328(13) A; Ag···Ag–3.3497(13) A and 3.3750(13) A; the values of chelate angles OAgO fall within 64.6(4)-71.1(3)°. Under thermogravimetric experiment conditions compound 1 decomposes within temperature range 100-385°С with formation of silver metal.

The discovery of unique magnetooptical properties of paramagnetic centers in silicon carbide, which make it possible to control spins of small arrays of centers of atomic sizes to single centers at room temperatures, using the techniques of optical detection of the magnetic resonance, posed a number of problems, among which one of the main ones is the creation of conditions under which spin relaxation effects are minimized. As studies of properties of spin nitrogen-vacancy centers in diamond showed, the main contribution to spin relaxation is made by the interaction with nitrogen donors, being a major impurity in diamond. A similar problem exists for silicon carbide, since nitrogen donors are also basic background impurities. The objective of this work is to study the spatial distribution of the spin density of nitrogen donors in two basic silicon carbide polytypes, i.e., 4H-SiC and 6H-SiC, to use this information for minimizing the interaction of nitrogen donors with paramagnetic centers in silicon carbide. The results of the study are analyzed by magnetic resonance methods; the spin density distribution on the nearest coordination spheres of nitrogen donors occupying carbon sites in silicon carbide is determined. It is concluded that paramagnetic centers in the 4H-SiC polytype, including silicon vacancies, can be more stable to the interactions with unpaired donor electrons, since electrons are not localized on the coordination sphere closest to the paramagnetic center in this case.

An optical quantum magnetometer with submicron spatial resolution is proposed that is based on the phenomenon of optical response in a solid-state spin system under conditions of spin sublevel anticrossing without using a resonance frequency. The system operation is demonstrated by example of spin defects in silicon carbide of various polytypes.

An optical quantum thermometer with submicrometer resolution is proposed. Its operation is based on the physical phenomenon of the optical response in a system of spin centers in silicon carbide under conditions of anticrossing of spin sublevels of the excited quadruplet state (S = 3/2) with temperature-dependent fine-structure splitting.

Individual nitrogen centers N0 and nitrogen pairs N2+ have been detected and identified in natural diamond nanocrystals by means of the high-frequency electron spin resonance method. The N0 nitrogen centers have been observed in synthetic diamond nanocrystallites with a size of less than 10 nm produced by high-temperature high-pressure sintering of detonation nanodiamonds. Thus, the possibility of the stable state of impurity nitrogen atoms in diamond nanoparticles has been demonstrated.

Electron spin resonance (ESR) is used to study the neutron transmutation doping of silicon crystals enriched with 30Si isotope: phosphorus donors and radiation defects produced in the course of transmutational doping are observed. The ESR signals related to the phosphorus uncontrolled impurity in 30Si before transmutational doping (the P concentration is ∼1015 cm−3) and phosphorus introduced by neutron irradiation with doses ∼1 × 1019 cm−2 and ∼1 × 1020 cm−2 (the P concentrations are ∼5 × 1016 and ∼7 × 1017 cm−3, respectively) are studied. As a result of drastic narrowing of the phosphorus ESR lines in 30Si, the intensity of lines increased appreciably, which made it possible to measure the phosphorus concentration in the samples with a small volume (down to 10−6 mm−3). The methods for determining the concentration of P donors from hyperfine structure in the ESR spectra of isolated P atoms, exchange-related pairs, and clusters that consist of three, four, and more P donors are developed. In the region of high concentrations of P donors, in which case the hyperfine structure disappears, the concentration of P donors was estimated from the exchange-narrowed ESR line.

Phosphorus-doped silicon 30Si monoisotope samples with a highly homogeneous impurity distribution at a concentration of 5 × 1016 cm−3 were obtained for the first time by means of neutron transmutation doping.

The λ 6708 A and 6103 A lithium lines in the high-resolution spectra of some sharp-lined roAp stars are analyzed using three spectral-synthesis codes STARSP, ZEEMAN2, and SYNTHM. The lines from the VALD database were supplemented with lines of rare-earth elements from the DREAM database and new lines calculated using the NIST energy levels. Our synthetic-spectrum calculations take into account magnetic splitting and other line-broadening effects. Lithium overabundances were found in the atmospheres of the stars based on our analysis of both lithium lines, along with high values of the 6Li-7Li isotope ratio (0.2–0.5). This can be explained if lithium is produced in spallation reactions and the surface 6Li and 7Li is preserved by strong magnetic fields in the upper layers of the stellar atmospheres, around the poles of the dipole field. The asymmetry of lithium lines to the red may be due to the action of shocks in the optically thin upper atmosphere, with the shocked material subsequently falling onto the star.

The infrared luminescence of Er3+ ions has been studied in bulk crystals of silicon carbide 6H-SiC doped with erbium in the process of their growth. The erbium centers of different symmetry in the crystals are revealed by the EPR technique. A number of intense luminescence bands of erbium ions are observed at a wavelength of about 1.54 µm. The luminescence can be excited by the light with quantum energies above and below the band gap of SiC. It is found that the luminescence exhibits unusual temperature behavior: as the temperature increases, the luminescence intensity abruptly rises starting with 77 K, passes through a maximum at ∼240 K, and, in the vicinity of ∼400 K, decreases down to the values observed at 77 K. The activation energies for the flare-up and quenching of the Er3+ luminescence are estimated at E A ≈130 and ≈350 meV, respectively. The mechanisms of the flare-up and quenching of the Er3+ luminescence in SiC are discussed.

EPR spectra of deep boron in 4H-SiC and 3C-SiC crystals have been observed and studied. Two sites in 4H-SiC produced deep-boron EPR signals, quasi-cubic k and hexagonal h. In both cases the deep-boron center symmetry is close to axial along the c crystal axis, and the g factor anisotropy is about an order of magnitude larger than that for shallow boron centers. In the 3C-SiC crystal, the deep-boron symmetry is also close to axial along one of the four 〈111〉 directions. The model proposed for the deep boron center with acceptor properties is BSi-v C, where BSi is the boron substituting for silicon, and v C is the carbon vacancy, with the BSi-v C direction coinciding in 4HSiC with the hexagonal axis of the crystal for both k and h positions. In the cubic 3C-SiC crystal, there are four equivalent deep boron centers, which represent BSi-v C pairs with the bond directed along one of the four 〈111〉 crystal directions.

The EPR spectra of scandium acceptors and Sc2+(3d) ions are observed in 6H-SiC crystals containing a scandium impurity. The EPR spectra of scandium acceptors are characterized by comparatively small hyperfine interaction constants, whose values are consistent with the constants for other group III elements in SiC: boron, aluminum, and gallium acceptors. The EPR spectra of scandium acceptors undergo major changes in the temperature interval 20–30 K. In the low-temperature phase the EPR spectra are characterized by orthorhombic symmetry, whereas the high-temperature phase has higher axial symmetry. The EPR spectra observed at temperatures above 35 K and ascribed by the authors to Sc2+(3d) ions, or to the A 2− state of scandium, have significantly larger hyperfine structure constants and narrower lines in comparison with the EPR spectra of scandium acceptors. The parameters of these EPR spectra are close to those of Sc2+(3d) in ionic crystals and ZnS, whereas the parameters of the EPR spectra of scandium acceptors correspond more closely to the parameters of holes localized at group III atoms, in particular, at scandium atoms in GeO2. It is concluded that in all centers the scandium atoms occupy silicon sites.

EPR studies of transition-element ions in SiC and GaN and of erbium in 6H-SiC are reported. Data are presented on Sc2+ ions and scandium acceptors, and chromium and molybdenum ions in various charge states in SiC. A study was made of nickel and manganese in nominally pure GaN grown by the sandwich sublimation method. The first EPR investigation of Er in 6H-SiC is reported. Erbium was identified from the hfs of the EPR spectra. Various possible models of erbium centers in silicon carbides are discussed. Strong room-temperature erbium-ion luminescence was observed.

The spatial distributions of the unpaired-electron wave functions of shallow N donors in SiC crystals and of shallow P and As donors in silicon crystals were determined by studying crystals with a modified content of the 29Si and 13C isotopes having a nonzero nuclear magnetic moment. As follows from the present EPR and available ENDOR data, the distribution of donor electrons in SiC depends substantially on the polytype and position in the lattice; indeed, in 4H-SiC, the unpaired electrons occupy primarily the Si s and p orbitals, whereas in 6H-SiC these electrons reside primarily in the s orbitals of C. The electron distributions for the N donor in the hexagonal position, which has a shallow level close to that obtained for this material in the effective-mass approximation, and for the donor occupying the quasi-cubic position differ substantially. The EPR spectrum of N in quasi-cubic positions was observed to have a hyperfine structure originating from a comparatively strong coupling with the first two coordination shells of Si and C, which were unambiguously identified. The effective-mass approximation breaks down close to the N donor occupying the quasi-cubic position, and the donor structure and the donor electron distribution become less symmetric. In silicon, reduction of the 29Si content brought about a substantial narrowing of the EPR line of the shallow P and As donors and an increase in the EPR signal intensity, as well as a noticeable increase in the spin-lattice relaxation time T 1. This offers the possibility of selectively studying these spectra by optically exciting a region of the crystal in order to shorten T 1 and thereby precluding EPR signal saturation only in the illuminated part of the material. This method may be used to advantage in developing materials for quantum computers based on donors in silicon and SiC.

Chromatin which was hydrodynamically sheared in a low ionic strength buffer lacking divalent cations (mu = 0.005) contains a heterogeneous set of DNP particles but no molecules of free DNA. The main finding is that a transference of sheared chromatin to 1-2 mM MgCl2 or to 0.1-0.2M NaCl results in the appearance of completely free DNA molecules. A salt-induced rearrangementof DNA-bound histones, but not a partial loss of them is responsible for the observed phenomenon. Formation of free DNA molecules is accompanied by aggregation of the majority of remaining DNP particles. Percentage of free DNA molecules in the chromatin which was sheared to an average DNA length of approx. 400 base pairs is increased from zero in the initial DNP sample to 8-9% in 1 mM MgCl2 and further to 30-31% of the total DNA in 0.30 M NaCl, 2 mM MgCl2. Free DNA molecules in the sheared chromatin are observed not only upon isopycnic banding of formaldehyde-fixed DNP in CsCl gradients but also in non-ionic Metrizamide gradients with either fixed or unfixed DNP samples. Process of free DNA formation is a reversible one; its direction and the equilibrium state depend in particular on the ionic conditions of the medium. Percentage of free DNA molecules in the sheared chromatin at a given ionic strength of solution is strongly decreased upon an increase of the average length of DNA in the DNP particles. Several lines of evidence suggest that free DNA molecules are formed in the sheared chromatin as a result of cooperative rearrangements of histones in salt-induced DNP aggregates. A dynamical model of chromosomal fiber is proposed on the basis of the present and earlier experimental data [1]. According to the model histones are arranged on DNA in clusters separated by stretches of free DNA. A salt-induced migration of histones along or between DNP fibers can result in unification of different clusters, thereby generating longer stretches of free DNA, the total amount of free DNA being approximately constant. Possible in vivo significance of such a dynamical structure is discussed.