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

By analyzing some known data of 3D atomic force microscopy for metallic materials and a number of other theoretical and experimental results, including data on the dislocation dissolution of cementite in pearlitic and martensitic steels, clustering in real Cottrell atmospheres (nanosegregations) is considered and their characteristics, including the number of impurity atoms per dislocation of atomic length, are determined, which differ significantly from those corresponding to classical theoretical models. In particular, Cottrell boron nanosegregations on edge dislocations in an ordered intermetallic compound FeAl containing 40 at % Al and 0.04 at % B, as well as Cottrell carbon nanosegregations on screw dislocations in martensitic steel, are examined. The presence of Fe₃B- and Fe₃C-type clustering in such nanosegregations, which is not taken into account in the framework of the classical models of Cottrell atmospheres (clouds), is shown. It is shown that in metallic materials (FeAl–B, Fe–C, Al–Fe, Pd–H) in real atmospheres (nanosegregations) on dislocations a certain clustering takes place (including the formation of boride-like, carbide-like, intermetallic-like, and hydride-like structures), which differs from that of the classical theoretical models of Cottrell atmospheres. In particular, the methodology for determining the impurity diffusion coefficient in the areas of nanosegregations on dislocations in metallic materials is considered using Pd–H, Al–Fe, and Fe–C systems as an example.

The problem of contamination of the inner surface of the gas-discharge chamber of a high-frequency ion thruster with sputtered material of the accelerating electrode is considered. A physical and mathematical model of electrode surface sputtering by secondary ions is formulated using the sputtering indicatrix. The motion of sputtered atoms through the flow of primary beam particles is considered, and the conditions for the penetration of sputtered material into the plasma of the gas-discharge chamber are determined. The motion of impurity atoms through the gas-discharge plasma is considered taking into account the possibility of impurity ionization. It is also assumed that all impurity atoms reaching the chamber surface are condensed. Numerical modeling of surface contamination for a spherical gas-discharge chamber using carbon and titanium as the material of the accelerating electrode of the ion-optical system is performed, regardless to the chamber material. The angular distribution of particles penetrating the chamber is obtained, and the maximum velocity and localization of particle deposition on the surface of the gas-discharge chamber are estimated. The results are in satisfactory agreement with published experimental data.

Compact neutron sources, including those based on bombardment of beryllium by a proton beam (e.g., DARIA project), assume using of targets with high thermal loading (~10 kW). To dissipate this heating power, we previously developed a concept of a rotating water-cooled target. Each proton pulse hit a new beryllium plate allowing distributing heating power over a large area and achieving good heat removal from the system. However, the cooling was not ideal: high water flow was required, leading to significant pressures near beryllium segments and creating a threat of their destruction during the operation of the device. Here, we consider a new and more efficient concept of water cooling suggesting that water flows normally to the cooled surfaces (jet cooling). Thermodynamic numerical simulations allowed us to estimate the maximum temperature of targets and water pressure near beryllium segments depending on the cooling water flow. We showed a significant improvement of all parameters of the device compared to the old concept of target assembly.

This article discusses the control of the lithographic plate movement in extreme ultraviolet scanners using optimal performance algorithms. The relevance of the topic is due to the new requirements of the semiconductor industry for positioning accuracy during the exposure of silicon substrates. Issues arising from chatter, unwanted oscillations caused by magnetostrictive drives, are addressed. An approach based on Pontryagin’s maximum principle and sliding mode control methods is proposed for damping oscillations. Various control functions, including the signum function and hyperbolic tangent, are investigated to minimize the negative impact of chatter on the mechanical system. Simulation results show that the use of smooth control functions effectively suppresses oscillations and increases positioning accuracy, which is critical for the fabrication of complex integrated circuits.

In this paper, the morphology and composition of stones obtained as a result of surgical interventions for sialolithiasis and cholelithiasis are studied. In the study of the pathogenesis of stone formation, X‑ray microtomography, X-ray fluorescence analysis, transmission scanning electron microscopy, X-ray spectral microanalysis, and Raman spectroscopy are used. Metal nanoparticles can presumably be structural components of crystallization centers or be embedded in the composition of antigenic structures in combination with protein and bacterial components under conditions of chronic endogenous inflammation.

Hydride phases TiZrTaV(Mo_1 – xNb_x) and TiZrTaNb(Mo_1 – xNi_x) (x = 0.2, 0.4, 0.6, 0.8) have been synthesized on the basis of a series of high-entropy alloys with a body-centered cubic lattice. The phase composition and type of crystal lattices of hydride samples were studied by X-ray diffraction. It has been established that the substitution of molybdenum with niobium or nickel in the alloys leads to the formation of hydrides samples with crystal lattices of various types.

The problems arising in the development of stationary plasma thrusters operating on krypton, which is an alternative to the traditional working substance for these thrusters, xenon, are analyzed. The basic physical concepts and research results that determined the development of stationary plasma thrusters operating on xenon are considered. It is shown that they can also be used in the development of thrusters operating on krypton taking into account its features as a working substance. One of the main features is the need to operate at increased krypton flow densities and discharge power in the acceleration channel. This leads to an increase in the flows of accelerated ions on the structural elements of the thruster and the rate of their erosion, and reduces the thrust efficiency and service life of the thruster. A review of studies carried out at the Research Institute of Applied Mechanics and Electrodynamics, Moscow Aviation Institute, on the possibility of reducing ion flows on the walls of the discharge chamber in a stationary plasma thruster operating on krypton in order to increase its thrust efficiency and service life is provided.

Two interference techniques for measuring the surface profile of extended samples from 60 to 200 mm in length have been developed. The profile is reconstructed by gluing separate frames taken with overlapping. It has been found that the angular reproducibility of the reconstructed profile in both techniques is less than 10 μrad, which corresponds to a profile height difference of about 10 nm. When measuring surfaces with curvature radii R > 1 m, it is recommended to use the stitching technique on a Zygo Verifire 4 highly coherent interferometer, which provides a complete surface map. For surfaces with curvature radii R < 1 m, only the stitching technique on a SuperView W1 white light interferometer is suitable. For particularly important measurements, it is advisable to use both methods to achieve maximum measurement accuracy. The results of the study confirm the effectiveness of the proposed approaches in the field of interference metrological control.

The synthesis of fullerenes C₆₀ and C₇₀ in an electric arc in the atmospheres of various gases, such as argon, helium, krypton, and hydrogen, at pressures in the range of 0.01–0.1 MPa was investigated. A stronger influence of gas-dynamic forces compared to the pinch effect on the possibility of obtaining a cathode deposit and a fullerene-containing soot with a falling volt-ampere characteristic was shown. The parameters of the electric arc, the structure of the cathode deposit, and the possibility of its production in various gases were determined. Spectral analysis of gas samples after experiments using hydrogen did not reveal the presence of hydrocarbons in the working atmosphere of the reactor. Selective deposition on a metal substrate under the action of a high-voltage electric field made it possible to separate a finely dispersed mixture of fullerenes C₆₀ and C₇₀ contained in the arc discharge plasma. It was found that the fractional composition of the C₆₀/C₇₀ fullerene mixture changes depending on the value of the substrate potential.

Studies have been carried out of the influence of a high-power ion beam of nanosecond duration on the atmospheric oxidation of polycrystalline magnesium. A decrease in the magnesium oxide phase was detected with increasing beam current density, which is probably due to the intensification of the processes of gas-dynamic expansion of the surface. Subsequent exposure of unirradiated and irradiated samples to a high-power ion beam at a temperature of 240°C in air led to a slowdown in the growth of the oxide phase in the irradiated samples. In this case, the greatest effect was observed for samples irradiated by a beam with a current density of 150 A/cm². The role of chemical processes, mechanical stresses, and structural changes occurring in the beam-modified zone and influencing the oxidation process is discussed. The observed nonmonotonic dependences of the ratios of oxygen and carbon concentrations to magnesium for different heating times are explained by the formation of not only magnesium oxide but also probably magnesium hydroxide and carbonate. It has been shown that the effect of increasing the oxidation resistance of magnesium irradiated with a high-power ion beam can also be influenced by an increase in the concentration of carbon during its penetration into the surface layer.