Journal of Surface Investigation. X-Ray, Synchrotron and Neutron Techniques

The most important condition for the stable operation of controlled thermonuclear fusion facilities is solving the "first wall" problems, which include the analysis of the interaction between thermonuclear plasma and in-vessel materials. Within this framework, the most pressing issue is the analysis of depth profiles of structural materials interacting with the plasma. This task is related to the fact that to reduce the average atomic number of the elements entering the plasma discharge, coatings made of low atomic number materials, such as lithium and boron, are used on plasma-facing components. This work presents a methodology for reflected electron spectroscopy that enables the depth profile analysis of targets with complex composition based on the interpretation of differential energy and angle spectra of reflected electrons. A method for calculating the energy spectra of electrons reflected from multi-component heterogeneous targets is introduced, based on the method of partial intensities, which has been repeatedly tested in numerous studies. Path length distribution function, which is the basis for the method of partial intensities and previously determined only within the framework of Monte Carlo simulations, has been established within an analytical approach. It is noted that to identify the depth profile of the distribution of components in the investigated target, a fitting procedure is employed, which is based on repeatedly solving the forward problem of calculating spectra of electrons reflected from a target of complex composition. A good agreement between the calculations and experimental results has been demonstrated. The simplicity of the experimental implementation of the reflected electron spectroscopy method is emphasized, as it does not require high-energy resolution equipment, since information about the target is extracted from the dome part of the reflected electron spectrum.

One of the most promising areas of research at the moment is the development of optical frequency summation and doubling systems, which use nonlinear crystals as an active element. Gallium phosphide (GaP) in the form of nanowires, which have a high dielectric constant and are transparent in the visible and infrared regions, can be used as a promising material for these elements. These crystals can be easily integrated into modern photonics systems due to their unique shape. In this study, we investigated the process of second harmonic generation in GaP nanowires, depending on their geometric parameters and the direction of incident radiation. We found the conditions that provide the highest efficiency of the generation process along the axis of the crystal. The possibility of the propagation of the second harmonic along the nanowire axis in air is demonstrated for specific parameters of the system — the diameter and angle of radiation. An increase in diameter leads to a reduction in the difference between the actual optimal direction and the predicted one, as the size- related characteristics of the filamentous nanocrystal tend to become more volumetric with increasing diameter. Results can be used to create various nanophotonic devices.

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 the ING-061 neutron generator. During the experiments, several sessions of irradiation of a 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.

We studied the kinetics of changes in the diffuse reflectance spectra and the integral absorption coefficient of solar radiation of the original CaSiO₃ powder with micron-sized grains and modified with CeO₂ nanoparticles at their optimal concentration of 3 wt% under electron irradiation (energy Е = 30 keV, fluence Φ = (1 - 7)×10¹⁶ cm^-2) and the possibility of recording these properties in a vacuum at the irradiation site (in situ). Modification was found to lead to an increase in radiation resistance from 2.39 to 2.89 times depending on the electron fluence. The modification efficiency increases with increasing electron fluence during irradiation. The obtained results can be used to develop new radiation-resistant thermal control coatings of the "optical solar reflectors" class for spacecraft.

The effect of preliminary He⁺ ion implantation on the morphology and microhardness of the surface of vanadium alloy V–10Ti–6Cr–0.05Zr–0.1Si upon subsequent exposure to high-power pulsed laser radiation has been studied. Low-activation vanadium-based structural materials are the most corrosion-resistant with respect to Li. They are promising for reactors with a liquid blanket version, where lithium is a coolant and tritium is a reproducible material. Helium ion implantation into alloy has been carried out in an ion-beam accelerator. General patterns of surface destruction have been established for both the original samples and those pre-irradiated with helium: formation of a hole surrounded by a breastwork and a heat-affected zone located behind the breastwork. The surface erosion is higher in samples implanted with helium: more intense material boiling inside the hole, the formation of a breastwork in the form of an annular rim and the formation of areas of three types in the heat-affected zone are observed. It is found that the microhardness of the alloy surface after He⁺ ion implantation and in the holes formed under subsequent exposure to laser radiation practically does not change (within the measurement error), and the microhardness in the holes of the original alloy first decreases when exposed to laser radiation, and then with an increase in the number of pulses, there is a tendency to its increase. The mechanisms of the observed phenomena are discussed.

The evolution of the phase composition of a metal-ceramic material formed by direct laser deposition using synchrotron radiation has been studied. Electron microscopy and X-ray phase analysis demonstrate that active formation of secondary phases of compounds occurs during repeated remelting in the process of multi-layer deposition. Insignificant formation of secondary phases occurs during single-track deposition due to the short lifetime of the molten pool. It is established that an increase in the concentration of secondary phases leads to an increase in the material microhardness.

The influence of laser radiation power density during laser shock treatment of titanium alloy BT6 on the properties of the surface layer: geometry, microhardness, degree of riveting, residual stress level and microstructure is studied. Comparative fatigue characteristics of samples strengthened in different modes of laser shock treatment are presented. Fractographic analysis is carried out and the relationship between the modes of laser shock treatment and the depth of fatigue crack initiation is determined.

Thin NiO films with thickness from 40 to 170 nm were obtained by pulsed laser deposition on c-Al₂O₃ substrates using the second harmonic of YAG:Nd³⁺- laser for ablation of a metal Ni target in a vacuum chamber at an oxygen pressure of 7.5 mTorr and substrate temperature of 370°C. Using X-ray diffraction, all NiO films were shown to have high crystalline perfection and the [111] orientation. The surface roughness of the obtained films is in the range from 1.6 to 2.3 nm. It was found that with increase in NiO film thickness, the charge carrier concentration decreased and the specific resistance increased. According to measurements of the optical properties of the films, the band gap increases from 3.43 to 3.63 eV with decreasing thickness.