Vol 13, No 6 (2019)

Comprehensive investigation into ordinary chondrites presented by the species of Markovka (H4 petrological type), Polujamki (H4 type) and Jiddat Al Harasis 055 (L4-5 type) is performed. The element and phase compositions, as well as the oxidation states of iron and nickel in the chondrites, are examined via micro X-ray fluorescence (micro-XRF), Mössbauer spectroscopy and synchrotron-based X-ray absorption spectroscopy. Elemental composition analysis is performed using micro-XRF, allowing one to obtain element distribution maps for the meteorite samples. According to Mössbauer spectroscopy data gathered on iron-containing phases, the chondrites consist mainly of olivine and goethite with a small amount of pyroxene and hematite. A low amount of troilite and kamacite is also observed in the Markovka and Polujamki specimens. The oxidation states of 3d metals in the chondrites are estimated from Fe and Ni K-edge X-ray absorption near-edge structure (XANES) spectra. Most nickel atoms in the meteorites are found to be in the Ni²⁺ state, while iron has an average oxidation state of +2.4 which is commensurate with the Mössbauer spectroscopy data. Infrared spectroscopy analysis of the chondrites is implemented as well. The results are important from the viewpoint of statistics acquisition on ordinary chondrites, as well as for further understanding of their formation.

An electroluminescent fission chamber is described, the operation principle of which is based on the optical detection of fission pulses. The use of an optical guide can significantly reduce statistical-measurement errors, lower the gamma-ray background, and increase the resistance to electrical and mechanical interference. Electroluminescence in strong electric fields with a large 10³–10⁴-fold increase in the light intensity allows one to detect individual fission events in the mode of counting. These advantages make it possible to measure the energy dependence of the cross section of the subbarrier fission of transuranium elements with a high resolution in lead in slowing-down spectrometers.

The geometric and band structures of cobalt-metahydroxide nanosheets, which are related to a new class of two-dimensional nanocatalysts for the hydrogen-release reaction, are calculated. As a result of improving the procedure, the optimal exchange-correlation functionals, basis sets, and dimensions of the “frozen” core are chosen to calculate the atomic and electronic structures, the density of states, and the width of the forbidden band. The calculated results show a decrease in the forbidden band of the cobalt-metahydroxide nanosheets compared with the crystal phase. The X-ray absorption spectra show a high sensitivity of the method to changes in the local atomic environment, especially in the first coordination sphere of cobalt atoms. The calculated model structure makes it possible to determine the features of the local atomic and electronic structures on a cobalt-metahydrixide nanosheet surface during the hydrogen-release reaction.

The analysis of the gradient structure-phase states and nanohardness of hypoeutectoid silumin at 120 μm depth after the processing by high intensive electron beams in the regime of top layer melting has been carried out. It has been shown that depending on the depth to the surface of irradiation the electron beam processing leads to the dissolution of the primary inclusions of silicon and intermetallides and the formation of structure of high-speed cellular crystallization of aluminium and the grains of plastic eutectic. A 1.5‒2 fold decrease in the concentration of the alloying elements has been detected. The hardness of irradiated silumin changes in a nonmonotonous way and reaches the maximum values exceeding the hardness of the initial state by 3.8‒4.2 times in the layer located at 30–50 μm depth. The interpretation of the observed changes in structure and hardness on irradiation has been given.

In ion sources, up to a third of the power released in a plasma discharge is carried away from the plasma in the form of ultraviolet radiation. Two main mechanisms for the formation of radiation are considered: radiation from excited atoms of the propellant and from ion-electron recombination coming out of plasma onto the surface bordering the discharge. The radiation-absorption coefficients of perforated electrodes of ion-extraction systems are determined.

The physical and mechanical properties of modern materials used for manufacturing optical-electronic space-based devices ensuring a high mirror roughness at a level of R_a = 1 nm are analyzed. The deposition of nickel obtained as a result of nickel reduction from aqueous solutions by the chemical method on a beryllium substrate to obtain an amorphous structure is studied. The coating is analyzed by X-ray methods. The phase and chemical composition of the coating is determined and its thickness is measured. The amorphous structure of the coating is confirmed. The coating has a high chemical resistance and hardness and provides conditions for effective optical polishing. Regulation of the chemical composition during the deposition process allows thermal matching of the coating with the substrate to be achieved.

The threshold structural instability arising in the thin layer of a nematic liquid crystal (nematic) along the surface of an electrode during the flow of a weak direct injection current is described. Local, limited in length L_у, nuclei (precursors) of electrohydrodynamic and flexoelectric instabilities are assumed to be in this thin layer. In the case of electrohydrodynamic instability, such precursors have been called “bullets” (solitons) because of their specific appearance, and their length L_у is a measure of local perturbation of the orientational structure of a nematic. In the case of flexoelectric instability, pieces L_у are formed by an irregular system of short polarized flexoelectric domains. Such an instability corresponds to a system consisting of groups of stripes, which are characterized by the opposite motion of “bullets” along these stripes and the average velocity of this movement.

A procedure for calculating the fractal dimension of tactoid structures of a 2D-nanofiller (graphene oxide) in the polymer matrix of a nanocomposite is proposed. The fractal nature of tactoids leads to the fact that only a part of their surface (the unscreened surface) is available for the formation of interphase polymer-matrix—2D-nanofiller contacts. An increase in the unscreened surface dimensions determines the enhancement of a relative fraction of the interphase regions and, as consequence, improvement in the mechanical properties of the nanocomposites. It is suggested that the interaction of graphene-oxide tactoids has a certain influence on the indicated properties.

The effect of the degree of tellurium doping on the structural characteristics (average sizes of grains and growth figures) of bismuth films in the concentration range 0.005−0.15 at % Te and the thickness range 0.3−0.7 μm is studied. The thicknesses of the investigated films are measured by multi-beam optical interferometry. The amount of tellurium in the film is considered to be equal to that in the initial bismuth single crystal with a previously known tellurium concentration. Additional control of the tellurium content in the initial crystal is performed using a time-of-flight LYUMAS-30 mass spectrometer. To determine the average sizes of grains and growth figures, I use the technique developed by E.V. Demidov. The studies conducted reveal that an increase in the degree of tellurium doping in bismuth films leads to a significant decrease in the growth figures. The weak effect of annealing on the crystallite size in tellurium-doped bismuth films indicates the high temporal stability of their structures.

The effect of accompanying ion-beam treatment on the structure and properties of SnO₂ films synthesized by the method of high-frequency magnetron sputtering at room temperature and at 200°C is investigated. It is established that ion-beam processing does not affect the transparency and the band gap of the obtained tin-oxide films. The refractive index and resistivity change. At room temperature, the films are X‑ray amorphous, and at 200°C they are polycrystalline. X-ray diffraction and electron diffraction studies show the presence of a single phase of SnO₂. Ion-beam treatment leads to a change in the preferred orientation of the crystallites. With increasing current of ion-beam processing, the grain sizes decrease.

The features of the spatial propagation and the evolution of a free correlated wave packet describing the process of particle motion are considered. It is shown that, unlike an “ordinary” noncorrelated packet, for which the process of spatial “spreading” and defocusing begins with the instant of its creation, in the case of a moving correlated packet, in the initial state, a self-simulated self-compression process occurs to the collapse state at a given distance; then the accelerated “spreading” mode is implemented. Some methods for forming such a packet and the possibility of using it in applied problems for particle and energy transport and for the aims of medical hyperthermia are considered.

We develop a concept of the CW proton linac with the parameters of 13 MeV 162.5 MHz 5 mA. This linac designed for compact neutron source DARIA is based on the linac designed for the project BELA. The different linac layouts were considered. The most perspective linac layout includes Radio Frequency Quadrupole (RFQ) and Drift Tube Linac (DTL) sections with 6D beam matching between them. The drift tube linac section has a modular structure and consists of the separated individually phased IH-cavities with beam focusing by quadrupole magnets between the cavities. This DTL structure provides linac compactness, tuning and commissioning “cavity by cavity”. Results of the beam dynamic simulation and radio frequency parameters of the linac cavities are presented.

The probability of the non-dipole emission of photons by channeled particle is calculated. The emission of hard photons with an energy comparable with that of the incident channeled particle is studied. The quasi-Bloch energy spectrum of an oriented fast charged particle entering a crystal at an angle smaller and greater than the Lindhard angle is calculated. The initial and final spectra of the channeled particle are described by different sets of band wave functions corresponding to different energies. The processes of photon generation by a quantum particle entering into the crystal at an angle larger and smaller than the Lindhard angle are considered on an equal basis. The spectrum of hard-photon emission is shown to consist of a set of well-observed emission lines.

The kinetics of the formation of radiation-induced defects in silicon and silicon carbide as a function of the absorbed energy is analyzed. The dependence of the concentration of conduction electrons n-Si and n-SiC on the irradiation dose is studied experimentally under conditions of irradiation with electrons with an energy of 0.9 MeV and protons with an energy of 15 MeV. The advantages and disadvantages of using the integral flux (fluence) and absorbed energy as kinetic parameters are discussed. It is established in the performed studies that the visual representation of the kinetics of radiation-induced defect formation as a function of the fluence of irradiating particles is clearer for tabulating the requirements imposed to equipment stability under suitable conditions. To study the physical processes underlying the formation of radiation-induced defects in semiconductors, it is more convenient to use the dependences of the effects observed under radiation exposure as functions of the absorbed energy.

This work is aimed at a comprehensive study of the processes of immobilization and conformational behavior of DNA on a zirconium-dioxide (ZrO₂) surface. The computer-aided molecular dynamics (MD) method is used to study model systems of nanoparticles and nanoscale DNA + ZrO₂ films, as well as elucidate the experimental spectral and integrated measurements, including the neutron-nuclear physical aspects of the study. Using hybrid MD potentials of classical mechanics and quantum chemistry for DNA solvated in an aquatic environment, the DNA/ZrO₂ surface interactions are studied, and different DNA damage scenarios with various charge modifications are simulated. The charge modifications are introduced into the central part of the DNA molecule by means of two phosphorus atoms, P_a and P_b, for which a number of MD models of DNA + surface are constructed, thereby estimating the dynamic changes of the distance D[DNA(P_a, P_b)-ZrO₂(O)] between the phosphorus atoms (P_a, P_b) and a selected oxygen atom on the surface of the ZrO₂ film. In conclusion, this work is aimed at the development of the functional heterojunctions, such as biological molecules with wide-gap dielectrics. These heterojunctions are intended for use in the field of molecular electronics, in particular, to create biochips and memory arrays in computer architectures of the future.

The present report describes a new phenomenon, namely the formation of a nanoscale hydrosol during short-term exposure of the surface of water by focused terahertz radiation of the Novosibirsk free-electron laser. The composition of the particles is completely determined by the material of the container used. Hydrosols are technologically convenient forms for scientific and industrial applications, which are characterized by uniform deposition and high catalytic activity used in medicine, optics, and as a suspension for sample preparation for chemical and elemental analysis. This article presents the results of our study of graphite particles formed in water, a suspension, which is in demand for industrial purposes. Commercially available high purity graphite (99.5%) of GE grade is used. The initial material and the resulting particles are studied using an atomic force and electron microscope with an elemental analyzer.

This paper reports on morphological and optical properties of Cu_1 – xZn_xO nanoparticles (x = 1 and 3 at %) synthesized by the microwave method. Undoped and Zn doped CuO nanoparticles are characterized by SEM, EDAX, UV–vis FTIR and XRD analysis. Capsule shape and Circle shape nanoparticles are observed in SEM analysis. The at % of Cu, Zn and O in nanoparticles is estimated by EDAX analysis. The presences of various chemical functional groups are confirmed by FTIR analysis. The peaks present in the range 410–430 cm^–1 are assigned to the Cu–O. The bandgap value is calculated as 3.94, 3.84 and 3.82 eV for undoped and Zn doped (1 and 3 at %) CuO nanoparticles. The average crystallite size of undoped CuO nanoparticles is calculated as 17.14 nm using the Scherrer formula by XRD analysis.

This work focuses on multilayer monochromatization systems (MMS) designed for X-ray spectroscopy stations of synchrotron radiation (SR) user-oriented centers for operation in a wide range of energy resolutions and at a high temporal resolution of the synchrotron experiment. The problem of providing a high SR flux density after the monochromator at required the monochromatization-system bandwidth is solved. A factor crucial for the quantitative analysis of the functional properties of the MMS is revealed and the optimum number of periods is determined. Analysis of the atomic and solid-state properties of elements and materials and detailed numerical simulation of the MMS allowed us to select several optimum pairs of materials for the synthesis of multilayer structures, in particular, Pt/Si and Au/Si. It is shown that reflectivities of more than 80% at a bandwidth of 4.4% can be achieved, which is very important for further practical development and the design of promising monochromators. The performed work concerns monochromatization systems for the SR energy range from 5 to 12 keV, which is the most sought after in X-ray spectroscopy.

The results of studying the X-ray photoelectron spectroscopy of the chemical composition of nickel surface layers with a deposited aluminum film, depending on the dose of irradiation with argon ions, are presented. Analysis of the spectra shows the formation of Ni₃Al aluminide during ion-beam mixing. The highest content (~20%) of this compound in the modified layer is observed at an implantation dose of 5 × 10¹⁶ cm^–2.

The initial growth stages of (11\(\bar {2}\)0) ZnO films on the rhombohedral plane of sapphire are studied. Grains of parasitic orientations are found to form at early growth stages. The pre-growth annealing of sapphire substrates at temperatures above 1000°C results in suppression of the growth of these grains. The presence of round and polygonal grains in (11\(\bar {2}\)0) ZnO films is explained from the standpoint of the cluster-growth mechanism.

Carbon nanotubes are obtained using chemical vapor deposition (CVD) equipment via the pyrolysis of natural gas in the presence of nanoscale iron. The influence of various parameters on the yield of nanomaterials synthesized is studied, and we find that the yield of nanocarbon increases with an increase in the pyrolysis temperature from 650 to 850°C. At the same time, the introduction of argon, which acts as a buffer gas, into the reactor significantly increases the yield of carbon nanotubes. The samples synthesized are studied by physical methods.

The fracture of surface layers of alumina ceramic (polycor) under the action of a high-power ion beam of nanosecond duration is investigated. The characteristic features of such fracture are determined. An estimation of the thickness of breakaway fragments of the surface layer of the ceramics gives values in the range from 4 to 12 μm at single high-power ion beam irradiation with a current density of 150 A/cm². Oxygen depletion in the surface layer of the ceramics is established. The effect of irradiation on the structural-phase state of the ceramics is considered. The possible mechanisms of the observed fracture are discussed.

The features of the field electron emission through a drop of a colloidal solution of a surfactant (structured colloidal solution of cetyltrimethylammonium bromide) are studied. The results indicate the possibility of using data on the angular distribution of the electron emission intensity stimulated by a pulsed electric field from structured liquid media to study the positional order and geometry of molecular associates in solutions.

The influence of the form of the Ar–Si interatomic potential on the results of simulating the physical sputtering of amorphous Si by low-energy Ar ions is analyzed. The yields of Si sputtering by Ar ions with an energy of 50–300 eV at normal incidence are calculated using the molecular dynamics (LAMMPS software) and the Monte Carlo methods by means of the MOTREV program developed at the Skobeltsyn Institute of Nuclear Physics, the Moscow State University, and used quantum-mechanical elastic-scattering cross sections. The semiempirical Molière and ZBL pair potentials and a potential developed on the basis of density functional theory calculations are applied to describe Ar–Si interaction. The energy dependences of the sputtering yields obtained using different potentials are analyzed in this paper. Conclusions concerning the applicability of the considered Ar—Si interaction potentials to simulation of the physical sputtering of amorphous Si in the indicated range of projectile energies are drawn.

The design and fabrication technology of test objects in the form of slit-like grooves with a rectangular profile and certified widths in the range of 50–500 nm in silicon are described. Experimental results that substantiate sections of the technology of groove fabrication and confirm the basic properties of the produced structures are given. The test objects are intended for calibrating scanning electron microscopes (SEMs) and studying the mechanisms of SEM-image formation.

A three-layer structure is fabricated on a low-resistance silicon substrate using plasma chemical etching. We study it experimentally and show that a substrate with such a structure can be used as an absorber of terahertz (THz) radiation in the frequency range of 0.5−2.0 THz. For this structure, absorbance in the indicated frequency range is measured to be more than 95%.

Active layers on the surface of AVCarb® Carbon Fiber Paper P50 and Toray Carbon Fiber Paper TGP-H-060 T carbon carriers are formed by the ion-beam-assisted deposition of platinum and one of the rare-earth metals (Ce, Gd, Dy, Yb, and Ho) as an activating additive in order to obtain electrocatalysts for the direct oxidation of ethanol and methanol for fuel cells with a polymer membrane electrolyte. The deposition of metal atoms and mixing of the deposited layer with the surface of the substrate with accelerated ions of the same metal are performed from the neutral vapor fraction and the vacuum arc discharge plasma of a pulsed electric arc ion source, respectively. A distinctive feature of the obtained electrocatalysts is their higher activity in the oxidation process of more complex ethanol molecules as compared with methanol.

The structure, phase composition and tribological properties of surface layers of hypoeutectic silumin after the complex processing including the electroexplosion alloying with the yttrium oxide powder in different regimes and the subsequent electron beam processing have been analyzed by the methods of modern physical material science. With respect to the initial silumin the ≈20-fold increase in the wear resistance and ≈1.5-fold decrease in the friction coefficient have been detected. The complex processing is accompanied by the formation of the multiphase submicro—nanocrystalline layer up to 80 μm in thickness enriched by yttrium and oxygen atoms responsible for the multiple increase in the wear resistance. At the complex processing according to the first regime of electroexplosion alloying (EEA) (Y₂O₃ powder mass—0.0589 g, discharge voltage—2.8 kV) with the subsequent electron beam irradiation, the major phase of the modified layer is the solid solution based on Al (≈71.2 mass %), the remaining phases are SiO₂, YAlO₃, YSi₂. The 1.5-fold increase in the mass of Y₂O₃ powder at EEA and 1.1-fold decrease in the discharge voltage is accompanied by the increase in the quantity of phases, the significant (more than 2.5-fold) decrease in the content of the solid solution based on Al, the ≈2.2-fold increase in the content of silicon oxide, the presence of yttrium oxide and metallic yttrium.