Vol 12, No 1 (2018)

As a result of the exposure of tungsten to a high-intensity plasma flow, it is established that the exposure of recrystallized and plastically deformed samples leads to fundamentally different mechanisms of confinement of plasma particles and associated deformation of the surface. The surface of the exposed deformed samples contains micrometer-sized ruptured blisters: an indication of the formation of subsurface bubbles on a grid of dislocations forming during deformation. Desorption spectra of both types of sample are decomposed into three peaks, corresponding to the detachment of plasma–gas particles from dislocations, deuterium-vacancy clusters, and pores. Plastic deformation, which leads to an increase in the dislocation density, does not change the position of the three peaks in the desorption spectra but increases their amplitude in comparison with the recrystallized material.

The applicability of the modified kinematic approximation for simulation of the specular reflection and the diffraction of a neutron beam from regularly ordered nanostructured objects on the surface and in the surface material layer is analyzed. The obtained results are compared with those of the real experiment and simulation of the distorted-wave Born approximation (DWBA). The influence of various factors on the obtained results is analyzed. These factors include the effect of neutron-wave refraction at the interfaces between media, the spectrometer-resolution function, and renormalization of the results for a nonspecular scattering signal based on data obtained for a specular channel. It is shown that, in many cases, it is possible to obtain rather good agreement with the experimental data and with the results of calculations using DWBA methods and of calculations using the Parratt algorithm.

The temperature dependences of the magnetization of polycrystalline samples of (NdSmDy)(FeCo)B sintered permanent magnets are measured in various magnetic fields by a SQUID magnetometer. Near T = 110 K, the spin-reorientation transition occurs. Bistable magnetic states with two equally possible orientations of the magnetization vector corresponding to different polarities of the permanent magnet are formed in the samples near the spin-reorientation transition. The polarity of the sintered magnets can be stabilized by a small external magnetic field of ∼250 Oe. It provides new possibilities for the application of these magnets in cryomagnetic systems such as magnetic undulators.

New experimental data are presented on the radiation-stimulated diffusion of hydrogen in metals, in particular, nickel and palladium, under the action of a 30-keV accelerated electron beam. Hydrogen desorption rates from nickel and palladium are determined for thermal and electron beam heating; a substantial shift of the thermal gas-desorption peaks to the low-temperature range is detected upon radiationinduced heating. The presence of an internal hydrogen atmosphere is shown to create favorable conditions for the vibrational-translational exchange (V–T exchange), non-equilibrium redistribution, and desorption of hydrogen from a solid upon irradiation. Accelerated hydrogen migration stimulated by electrons with an energy below the defect-formation threshold is explained at a qualitative level. First-principles calculations of the electronic structure of the metal–hydrogen system reveal that plasmons are also an efficient mechanism for radiation-energy dissipation over the whole crystal.

The principles of constructing a sputtering-type high-current source of homogeneous and heterogeneous cluster ions are comprehensively analyzed. The results of analysis are used to perform computer simulation of the given source. The ion-optical scheme and structural model of a new cluster ion source are developed.

The formation of molecular water clusters is simulated using the theoretical density functional theory/ B3LYP/6-311+G(d,p) method. The spatial configurations of 29 clusters with 2 to 28 water molecules are calculated. The dipole moments, the complete complex-formation enthalpy, and the enthalpy of the successive joining of water molecules are determined with the basis-set superposition error taken into account. The features of the geometric structure and the hydrogen-bond strength of water clusters are analyzed on the basis of the obtained theoretical data. The complex-formation enthalpy is revealed to depend periodically on the number of water molecules in a cluster. It is found that clusters with molecules whose number is a multiple of four are energetically most advantageous. When a molecular cluster is built starting with 17 molecules, the cluster structure is changed, resulting in that one end of the complex rolls up into a prismatic configuration.

Heat-transfer- and thermocapillary-convection macroprocesses observed during direct laser metal deposition (DLMD) with coaxial powder injection are examined. The study is performed using the 3D mathematical model incorporating self-consistent equations for free surface evolution, heat transfer, and hydrodynamics, which allow for powder-particle embedding into the thermocapillary convection zone under DLMD. The processes under consideration refer to the main ones underlying additive laser technologies, which determine the microstructural properties and quality of synthesized parts. The convection-diffusion equations are numerically solved using the final volume method. Calculations are carried out for the thermocapillary convection of H13 steel powder. The influence of laser-radiation characteristics (power, scanning rate, intensity distribution in the beam) and the powder-mass flow velocity on temperature fields, the structure of convective melt flow (including a maximum melt velocity), and the geometric characteristics (height and width) of the object formed is investigated.

Single crystals of bismuth-germanate grown by the Czochralski method and possessing a combination of piezoelectric, electro-optical and magneto-optical characteristics are studied. The possibility of the non-destructive quality control of the grown crystals by X-ray diffraction investigation of their natural lateral faces is shown.

Algorithms for using the Galerkin projection method and the projection least squares method to analyze the three-dimensional model of the diffusion of minority charge carriers generated by an electron probe in a semiconductor material are presented. The results obtained using these methods are compared with the analytical solution. An estimate of the error is given, and the condition for the computation stability of the projection least squares method in the form of the limiting relation is obtained.

Over recent decades, the diffraction of thermal neutrons has become a powerful tool for solving various actual problems of materials science. To carry out scientific investigations on this theme, a neutron time-of-flight Fourier diffractometer FSD was developed and has been successfully operated for many years at the IBR-2 pulsed reactor in the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna. To ensure high resolution of the instrument, a special correlation technique is used, i.e., a fast Fourier chopper for modulation of the primary-neutron-beam intensity and the reverse time-of-flight method for data acquisition. The current state of the FSD diffractometer and its capabilities are described and examples of performed experiments are given.

The results of the combined investigation of the chemical composition of the Bosporan King Rhescuporis V’s billon staters from the 2011 Phanagorian hoard by XRF spectroscopy, neutron tomography and diffraction, and metallographic analysis are presented. The study of the crystal structure of the coin alloy indicates the absence of silver coating of staters minted from low-grade silver.

The search for microinclusions of light platinoids (Ru and Pd) in samples of the Bushveld intrusion complex (South Africa) and corresponding examination are performed by scanning X-ray fluorescence analysis at the SR XRF experimental station with the help of the VEPP-3 storage ring at the Collective-Use Center “Siberian Synchrotron and Terahertz Radiation Center” based at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences. The samples are prepared as plane parallel ground plates 2 mm in thickness. First, one-dimensional scanning with a wide beam (1 × 20 mm) of monochromatic radiation with an excitation energy of 20 and 30 keV is performed. Then, the region with higher contents of light platinoids is two-dimensionally scanned with a beam (30 × 45 μm) which is focused with a polycapillary lens. Sample surface mapping enables identification of a few individual particles 50–100 μm in size with a high Pd content. The potential for micro-XAFS investigation of an individual particle is demonstrated.

The principles of the formation of detonation nanodiamond–polymer thin-film nanocomposites which are promising materials for highly cost-effective field electron vacuum cathodes are studied for the first time. The coatings are deposited onto oriented substrates (Ni, Si) in the processes of self-assembly from an evaporating aqueous solution by the spin-coating technology. Field electron emission studies show that the threshold voltage exceeds values typical for nanocarbon structures by more than ten times. At the same time, it is nearly ten times lower than the work function in macroscopic diamond or graphite. An improvement in the stability of the emission properties of the coating in the presence of polymers in comparison with the deposition of films from a solution of nanodiamond crystallites without polymers is established.

The results of an integrated experimental study of the effect of doping nickel additives (0.4 and 1.0 wt %) on the kinetic processes that occur during the artificial aging of copper–beryllium alloys in a constant magnetic field are described. A “negative” magnetoplastic effect, the magnitude of which reaches ∼35%, is discovered. The presence of nickel additives leads to a significant increase in the microhardness of the alloys and a change in their lattice parameters and fine structure; however, a change in the quantitative content of additives from 0.4 to 1.0 wt % ambiguously affects the measured quantities.

The concept of nanofractality is developed. Models describing the appearance of nanofractality in objects of different dimensions are presented. For two-dimensionality, analysis is based on the modification of Tamm states on fractal surfaces. In this context, the appearance of different effects is analyzed. The fractality of the free and internal surfaces of nanoobjects is found to affect their electronic spectrum, which can lead to radical modification of the physical and chemical properties of nanostructures.

The morphology of the surface of thin films of uranium bis-phthalocyanine and its pyrolysed derivatives is analyzed by atomic-force microscopy. During the pyrolysis of samples in an inert atmosphere (400–800°C), the transition from a crystalline to amorphous carbon structure with immobilized metal atoms is observed in uranium bis-phthalocyanine thin films deposited onto a substrate. It is found that at temperatures above 1000°C the pyrolysis is accompanied by the aggregation of nanoscale particles and the formation of ultraporous matrices with a high specific surface area (∼102 m²/g).

An expression for the Helmholtz free energy is established and the equation of state is derived for a nanocrystal containing vacancies in the lattice and delocalized (diffusing) atoms. The calculations are performed for bcc (body-centered cubic) iron under the isothermal compression of a nanocrystal along the 300-K and 1000-K isotherms. The changes in the specific surface energy (σ), the probability of vacancy formation (ϕ_v) and the probability of atom delocalization (x_d) are studied depending on the size (N) and shape of the nanocrystal at different temperatures (T) and pressures (P). The size dependences are characterized along two isobars: at atmospheric pressure (P = 1 bar) and at P = 100 kbar. As is shown, two P-points arise in the σ(P) isotherms at T ≤ 300 K, where the specific surface energy is independent of the nanocrystal size, which is σ(N) = σ(∞). As the temperature increases, the P points approach each other and at T ≥ 1000 K they vanish in the isotherms. At atmospheric pressure and T = 300 K the amount of vacancies per atom in a nanocrystal is much lower than that in a macrocrystal; however, at T = 1000 K the shredding of the latter leads to an increase in the probability of vacancy formation. Moreover, the smaller the nanocrystal size, the higher the probability of atom delocalization (as well as the self-diffusion coefficient) at any pressure and temperature. The ratio ϕ_v/x_d decreases with decreasing size of the nanocrystal, and less than a certain size, there is an no-vacansies self-diffusion, at which the number of delocalized atoms is greater than the amount of vacant cells in the nanocrystal lattice, i.e., ϕ_v < x_d. As the nanocrystal shape becomes different from the energetically optimal, the size dependences of the lattice properties of the nanocrystal are enhanced.