Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques最新文献

A technique has been proposed for deposition of Nb–Ti coatings on titanium alloy Ti₆Al₄V by electric spark treatment in a mixture of titanium granules with the addition of niobium powder from 2 to 6 vol %. The results of the structural study of the obtained coatings by metallography, X-ray analysis, and scanning electron microscopy are presented. It was shown that the thickness of the coatings is in the range from 31.8 to 35.9 µm. The structure of the coatings is represented by the β-phase of an Nb–Ti alloy with a niobium concentration from 44.6 to 49.1 at %. The corrosion properties of the coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution, and the cyclic oxidation resistance of the samples was investigated at a temperature of 900°C for 100 h. It was shown that the Nb–Ti coatings, contrary to literature data, do not improve the anticorrosion properties of the Ti₆Al₄V alloy. The microhardness of the coatings was studied under a load of 0.5 N, and the tribological properties were examined in dry sliding mode under a load of 25 N. It was shown that the hardness of the prepared Nb–Ti coatings is 4.9–4.95 GPa and the friction coefficient is in the range from 0.88 to 0.74. The deposition of electrospark Nb–Ti coatings using the proposed method makes it possible to increase the wear resistance of the surface of titanium alloy Ti₆Al₄V up to 11 times.

One of the current research areas is the development of optical frequency summation and doubling systems in which nonlinear crystals serve as the active element. Gallium phosphide (GaP) in the form of filamentous nanocrystals, which has a high quadratic dielectric constant and is transparent in the visible and infrared ranges, can be regarded as a promising material for such systems. Owing to their shape, these crystals can be effectively integrated into modern integrated photonic systems. A numerical study was carried out on the process of second harmonic generation in GaP nanowires as a function of their geometric parameters and the orientation of the incident radiation. The conditions that provide the highest generation efficiency along the nanocrystal axis were determined. The possibility of second harmonic propagation along the axis of filamentous nanocrystals in air was demonstrated for specific system parameters—namely, the transverse size of the nanocrystal and the angle of incidence of the radiation. An increase in the transverse size of the structures leads to a reduction in the difference between the actual and predicted propagation directions, since the size-related characteristics of the filamentous nanocrystal tend to become more volumetric with increasing diameter. The results can be used in the development of various nanophotonic devices.

The passage features of a beam of relativistic charged particles (electrons or positrons) through a single crystal along densely packed crystallographic planes or axes, as well as the characteristics of the resulting electromagnetic radiation, are determined by the possibility of capturing particles in the channeling mode and their distribution by quantum states with different transverse motion energies. An accurate quantum calculation of the populating coefficients for different quantum states of the transverse energy spectrum is mathematically very difficult and analytically possible only for the simplest model potentials. For the more realistic potential models of plane or axial channels in crystals the only available possibility is to make estimations using classical or quasi-classical approximations. The article provides calculations and evaluations of the quantum states population probabilities for planar channeling. It is demonstrated that even for collimated particle beams, when the particle capture probabilities are high enough, the particles distribution by transverse energies in planar channel is close to even. The possibility of resonant capture in the axial channeling mode for electrons entering single crystal with angular momentum values relative to the crystal axes multiples of the Planck constant is also evaluated.

The development of nanowire growth technology based on the GaPNAs solid solution is of interest for modern photonics. A structural analysis of core–shell GaPNAs/GaP nanowires grown on a Si(111) substrate using the self-catalyzed molecular beam epitaxy method has been performed. Transmission electron microscopy has shown the formation of a core and a composite shell in the nanowire body. The twinned sphalerite phase and non-twinned wurtzite phase have been determined. Scanning electron microscopy has revealed the formation of a continuous layer of islands on the sample surface when a nitrogen flow is turned on, which confirms embedding of nitrogen into the grown structures. It was impossible to separate the diffraction reflections of the core and shell of both the sphalerite and wurtzite phases using X-ray diffraction analysis with reciprocal space mapping. The average lattice constant of the sphalerite phase was found to be 5.458 ± 0.005 Å, as well as the average lattice parameters of the wurtzite phase: a = 3.87 ± 0.01 and c = 6.28 ± 0.01 Å. The fact that the phase lattice constants are indistinguishable in the nanowires confirms the possibility of creating high-quality low-defect GaPNAs/GaP nanowires.

The work is focused on the analysis of the influence of direct electric current and constant magnetic field on the strength and plastic characteristics of the polycrystalline alloy Zn–Al–Cu–Mg. The results prove that weak magnetic fields significantly affect the plastic characteristics of the materials under study. The effect of magnetic field depends on the magnetic induction magnitude. Microhardness and the creep rate increase significantly under the influence of magnetic field under direct current flow conditions.

The aim of this paper is to determine the optimum wavelength interval for non-contact measurement of temperature and emissivity using the least squares method (LSS) in the gray body approximation, where the measurement uncertainties of these parameters will be minimal. Analysis of the statistical uncertainty of the remote temperature measurement reveals that the both uncertainties of the temperature and emissivity measurements have minima at the wavelength close to that of the Wien’s displacement law. The relationship between optimal wavelength, λ_min, and temperature, T, is obtained in the paper.

The results of a study of deuterium ion saturation of a textured polycrystalline diamond target are presented. Deuterium implantation into a polycrystalline diamond target was carried out by a deuterium ion beam at the HELIS accelerator (LPI RAS) at a deuterium ion energy of 25 keV and a beam current of 30–35 µA. Fast neutrons formed in the reaction of deuterium nuclei synthesis in the target were detected. Neutron registration was carried out by scintillation detectors with organic crystals. The calibration of the scintillation detectors was performed using an ING-061 neutron generator. During the experiments, several sessions of irradiation of the polycrystalline diamond target with a beam of deuterium ions were carried out. The yield of neutrons from the target was recorded depending on the irradiation time and the time between irradiation sessions. A simulation of the passage of deuterium ions in diamond was carried out. According to the experimental results, taking into account the calculations of the energy of deuterium ions and the cross section of the nuclear reaction (d + d), depending on the depth of deuterium passage into the target, the values of deuterium concentration in the surface layer of the polycrystalline diamond target were obtained.

A signal processing technique for X-ray photoelectron spectroscopy has been developed based on the interpretation of both the peak area and the energy-loss region adjacent to the photoelectron peaks. The methodology is derived from the method of partial intensities. The results of calculations of partial coefficients obtained in the small-angle approximation are in good agreement with those performed using Monte Carlo simulation. It is noted that calculating partial coefficients in the small-angle approximation allows obtaining analytical expressions that considerably reduce computation time compared with the Monte Carlo simulation method traditionally used for such calculations. This methodology has enabled the analysis of changes in the allotropic structure of materials subjected to helium plasma under conditions simulating the plasma–wall interface in nuclear fusion devices. Changes in the allotrope type of MPG-8 grade graphite and tungsten under plasma exposure have been studied. It has been shown that the surface of the MPG-8 sample acquires a structure resembling pyrolytic graphite as a result of plasma exposure. It has been established that the dielectric permittivity of tungsten does not change when tungsten “fuzz” forms on the surface due to plasma action. Growth of tungsten carbide as a result of plasma exposure has also been observed.

Boron carbide films deposited by sputtering of powder and solid B₄C targets in different frequency modes of magnetron operation (13.56 MHz, 50 kHz and DC) on Si and glass substrates at temperatures of 200–500°C and argon pressure up to 12 mTorr have been investigated. It was found that the magnetron sputtering of the powder target is characterized by higher values of target surface temperature (up to 900°C) and discharge voltage (up to 850 V). Films deposited by sputtering of the powder target at 50 kHz have lower microhardness (up to 16 GPa) and increased boron content by ~20%, film deposition rate (up to 3.5 μm/h) is 30–50% higher as for the solid target. The films are found to be X-ray amorphous. The root mean square (RMS) surface roughness of the films measured by atomic force microscopy was 16–19 nm over an area of 100 × 100 μm.

The review presents currently available data on the processes occurring during irradiation of reduced activation ferritic/martensitic steels with low-energy (≤200 eV) deuterium plasma. The mechanisms of formation of rough nanosized structures on the surface of steels, which affect the sputtering yields of these steels, are considered. The parameters of the transfer of hydrogen isotopes in these steels, obtained from experiments on gas permeability and plasma irradiation of hydrogen isotopes, have been collected. The results of studies on the accumulation of deuterium in steels without and containing radiation-induced defects are discussed.