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

The work is devoted to a technique for measuring the speed of sound when passing through a thick layer of “poured” nanopowder in an immersed state. A simple experimental setup is proposed consisting of two speakers and one microphone immersed in a container with a nanosized powder. The setup does not require calibration. Two indirect methods for determining speed in the nanopowder using two speakers and a microphone located at different distances from the speakers are shown. Experimental measurements are carried out in a silicon dioxide nanopowder with an average particle size of about 50 nm. It has been established that the speed of sound in this medium is less than that in gas and solid matter and is equal to 35 m/s. It has been shown that the speed of sound does not depend on the frequency of sound for frequencies up to 1600 Hz. A new hypothesis has been proposed that the nanopowder behaves like a new type of continuous medium, “heavy gas,” when a sound wave passes through it. The hypothesis allows one to apply formulas for determining the speed of sound in gas for this case. Based on experimental data, the adiabatic constant for the “heavy gas” is estimated. The proposed application of the effective medium approximation, such as the Hertz–Mindlin contact theory, to estimate the speed of sound in nanopowder shows that the nanoparticles are not in close contact with each other. This can be explained by the inapplicability of this theory to the case of “poured” nanopowder due to the packing of nanoparticles that differs from the theory.

The influence of temperature of amorphous SiO₂/Si substrates on the formation of ultrasmooth highly oriented ZnO(0001) films by direct current magnetron sputtering has been studied. It has been shown that ZnO films obtained at a substrate temperature of 500°С have a lamellar shape of crystallites regardless of the growth rate in the range 1–7 nm/s. This feature of the crystallite morphology is associated with a minimum root-mean-square surface roughness of 0.9 nm for traditional high-speed deposition methods. The ultrasmooth surface of the films and the lamellar shape of the ZnO crystallites are mainly due to the two-dimensional mechanism of film formation under conditions of charging the growing surface in the magnetron discharge plasma.

A high-entropy TiZrNbMoTa alloy with a body-centered cubic lattice has been synthesized. The interaction of the alloy with hydrogen is accompanied by the formation of samples containing hydride phases with tetragonal and cubic lattices. Hydrogen desorption from the hydride at a high temperature leads to the formation of a fine metal powder of the original alloy with the cubic lattice. Samples of the alloy and hydride phases are analyzed by X-ray diffraction and electron microscopy.

The study is conditioned by the need to improve the operational reliability of underground trunk pipelines. This is primarily due to the active development of pipeline transportation of hydrocarbons and increasing the raw material potential of the Russian Federation. During operation at low temperatures, the accumulated moisture can cyclically freeze-melt, expand and mechanically damage the waterproofing. An effective method is modification of the atmospheric pressure sliding arc in plasma, which provides a high degree of modification without deterioration of the strength and optical properties of the films, due to the absence of vacuum equipment and uniformity of modification of the polymer film surface.

Vacuum ultraviolet radiation is a part of ultraviolet radiation with a very short wavelength and is a component of cosmic radiation. Composite materials based on polyimide have great potential for protection against cosmic radiation. The paper presents the results of studies on the effect of vacuum ultraviolet radiation on a polyimide film, a polyimide track membrane, and a composite material based on the polyimide track membrane filled with silica nanofibers. Mass losses, dielectric properties, Fourier-transform infrared spectra, and wettability of the studied samples before and after vacuum ultraviolet irradiation were studied. It was found that the lowest mass losses during vacuum ultraviolet irradiation were observed in the composite material based on the polyimide track membrane filled with SiO₂; the dielectric constant of the composite film after vacuum ultraviolet irradiation increased by 65.8%. It was established that the effect of vacuum ultraviolet radiation on the films under study was accompanied by destruction of a small number of the following bonds: C=O, C–O, C–C, and C–N. At the same time, vacuum ultraviolet radiation caused the least damage to the developed composite material. Contact angle analysis of the studied samples showed that the surface of the polyimide film, polyimide track membrane, and composite material remained hydrophilic after irradiation. No changes were detected in the structure of the film surface.

The synthesis of gallium(II) sulfide was carried out from elements in a closed volume using a two-temperature method. Passivation of the gallium surface in vacuum was observed up to temperatures of 1623 К. The controlled chemical reaction was carried out in a hydrogen atmosphere at a pressure of 1300–2600 Pa. Similar results were achieved in vacuum using photocatalysis with ultraviolet radiation at a wavelength of 240–320 nm with a radiant power of 24.6 W. In both cases, at a temperature of 1323–1373 К gallium(II) sulfide synthesis took no more than 30 min with a loading mass of 100 g. The Rietveld method was used to characterize crystalline gallium(II) sulfide by powder X-ray diffraction. The results of analysis showed that the product of the chemical reaction was a single-phase GaS. The proposed solution to the problem of gallium melt surface passivation for sulfur oligomers from the point of view of quantum electrodynamics made it possible to significantly reduce energy costs and increase the synthesis efficiency of extrapure gallium(II) sulfide for its further use in chalcogenide glasses production.

This study examines the impact of mechanical damage to an X-ray interferometer block on its observed X-ray diffraction pattern. The origin of contrast resulting from imperfections in the crystal structure of the interferometer block, which arises from mechanical damage, is interpreted. Both theoretical and experimental evidence demonstrates that the curvature of interference fringes in the Moiré topogram is a result of scratches on the surface of the crystal block of the X-ray interferometer. The study determines the relationship between the period of the Moiré fringes, dislocation density, and their displacement. The average dislocation density near the center of the scratch is calculated. The study shows that the period of the Moiré pattern is inversely proportional to the dislocation density. Experimental evidence demonstrates that changes in the Moiré pattern also occur in the presence of dislocations in the crystal, which form as a result of a scratch on the surface of the crystal block of the X-ray interferometer. The geometric parameters of the scratch on the surface of the interferometer’s crystal block are determined. The depth of the scratch and the extent of the dislocation group aligned along the scratch are calculated.

New metal–ceramic laminated composites Ta/Ti₃Al(Si)C₂–TiC were obtained by spark plasma sintering. The samples were synthesized at a temperature of 1250°C and a pressure of 50 MPa for 5 min. For formation of the composites, preceramic paper with a powder filler based on the MAX phase of Ti₃Al(Si)C₂, as well as metal foils made of tantalum, were used. The phase composition, microstructure, and elemental composition were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy, respectively. It was found that as a result of sintering, dense multilayer composites were formed, consisting of tantalum metal layers, ceramic layers containing Ti₃Al(Si)C₂, TiC, and Al₂O₃ phases, as well as reaction layers ~13 μm thick at the metal–ceramic interface enriched with Ta, Al, and Si. Based on the mechanical test data, the ultimate bending strength of the obtained composites was determined (σ_bs = ~430 MPa). Metal–ceramic laminated composites with a refractory tantalum layer were shown to exhibit a ductile fracture mechanism accompanied by a more than fourfold increase in absolute deformation compared to a Ti₃Al(Si)C₂-based ceramic composite. This is achieved due to deflection, branching of cracks at the metal–ceramic interface, and plastic deformation of tantalum layers.

The experimental results of a study of the influence of ion etching of single-crystal films of cation-substituted iron-garnets on their structural, magnetic, optical, and magneto-optical properties are presented. It is shown that the ion etching of single-crystal garnets significantly reduces the surface roughness. Analysis of the domain structure, ferromagnetic resonance spectra, and magneto-optical hysteresis in the epitaxial film of bismuth-substituted iron-garnet during layer-by-layer ion etching shows the presence of three different layers, the state of which changes relative to the compensation point and the interfaces of the layers correspond to the transition through the compensation point. It is shown that the position of the layer interfaces can be varied by changing the temperature of the sample. A study of optical and magneto-optical characteristics shows that in single-crystal (epitaxial) films of iron-garnets, ion etching does not worsen optical transmission and does not destroy the garnet structure down to a thickness of tens of nanometers (the Faraday effect is preserved).

Using the method of reactive anodic evaporation of titanium in an arc discharge in a system with a self-heating hollow cathode in a gas mixture Ar + C₂H₂ + N₂ with the addition of hexamethyldisilazane (HMDS) vapors, dense homogeneous TiSiCN nanocomposite coatings with a thickness of up to 15 µm, a hardness of up to 43 GPa, and a wear coefficient of 2.8 × 10^–14 m²/N were obtained. It has been shown that by changing the pressure, composition, and activation degree of the vapor–gas mixture, it is possible to change the microstructure and properties of the obtained coatings within a wide range. An increase in the fluxes of C₂H₂, N₂, and HMDS, as well as the discharge current leads to an increase in the coating deposition rate. However, coatings with the optimal microhardness and wear resistance were obtained at a low discharge current of 10 A, a relatively low content of C₂H₂ (1 cm³/min) and HMDS (0.3 g/h), exceeding of which leads to a decrease in the hardness of the films and deterioration of their quality, which can be explained by excessive ionic exposure and nonoptimal chemical and phase composition of coatings. The chemical and phase compositions of the obtained coatings were studied. The coating structure is a nanocomposite consisting of TiCN nanocrystallites dissolved in an amorphous SiCN matrix.