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

The work is aimed at studying the properties of the “guiding” effect, namely the possibility of generating electromagnetic radiation when guiding beams of accelerated electrons. In this paper, we discuss a model of motion for the case of electron guiding during the interaction of electron beams with a dielectric surface. It is noted that when an electron beam is pressed against the surface of a dielectric by an external transverse electric field, in this case, due to the guiding effect, the electrons experience transverse vibrations when moving along the surface. Consequently, the movement of electrons in the transverse direction is accelerated and, accordingly, electron beams in the case of guiding should be a source of electromagnetic radiation, similar to the radiation of undulators and wigglers. The numerical estimates carried out in the work using the Larmor formula show that the power of this radiation should have a value sufficient for its experimental detection. This radiation should be of a pulsed nature against the background of continuous radiation. The power of the pulsed radiation must be several orders of magnitude greater than the power of the continuous background radiation.

In this paper, we study the anisotropic properties of a layer of carbon nanotubes upon electron reflection. Only a small proportion of the incident electrons is found to be reflected from a target with a surface layer of oriented carbon nanotubes. Reflection occurs only from a layer of horizontally oriented nanotubes at an incidence angle greater than 80° and vertically oriented nanotubes at an incidence angle less than 10°. The effect is explained by the peculiarities of the formation of an electron flow in the surface layers of the target.

A comparative analysis of the diffuse reflectance spectra and their changes after irradiation with electrons with an energy of 30 keV of coatings based on polymethylphenylsiloxane resin and pigment powders of two-layer hollow ZnO/SiO₂ particles is carried out. The analysis is performed in situ in the range of 250–2500 nm. The samples are irradiated using a Spectrum space-conditions simulator. The radiation resistance of the studied coatings based on two-layer hollow ZnO/SiO₂ particles is estimated relative to coatings based on ZnO polycrystals by analyzing the difference diffuse reflectance spectra obtained by subtracting the spectra after irradiation from the spectra of the unirradiated samples. It is found that the intensity of the induced absorption bands in coatings based on hollow ZnO/SiO₂ particles is less than in coatings based on ZnO microparticles, and the radiation resistance when estimating changes in the integral absorption coefficient of solar radiation (Δα_S) is twice as high. The increase in the radiation resistance is probably determined by the different nature of defect accumulation: in the case of solid microparticles, defects can accumulate inside grains; in hollow particles, the accumulation of defects can occur only within the thin shell of the sphere.

The application of mathematical models and artificial neural networks for predicting the properties of diffusion coatings created by thermal–chemical treatment based on the boroaluminizing process is considered. The formalization and analysis of forecasting experimental results are conducted. Building computer models for prediction based on experimental data of the boroaluminizing process with high accuracy is a solvable task when using artificial neural networks such as a multilayer perceptron. Testing the number of hidden layers and the number of neurons in them revealed the highest correlation coefficient R = 0.99993 for an artificial neural network using two hidden layers with ten and six neurons, respectively. The highest efficiency can be achieved using the hyperbolic tangent activation function.

The effect of deformation nanostructuring on the ion-beam erosion of copper at a high fluence of irradiation with 30 keV argon ions is experimentally studied. To form an ultrafine-grained structure with a grain size of ~0.4 μm in copper samples with an initial grain size of about 2 μm, deformation nanostructuring by high-pressure torsion is used. It is found that when a layer with a thickness comparable to the grain size is sputtered, a steady-state cone-shaped relief is formed on the copper surface, the appearance of which does not change with increasing irradiation fluence. It is shown that the smaller the grain size in copper, the greater the concentration and the smaller the height of the cones on the surface. The cone inclination angles, close to 82°, as well as the sputtering yield of 9.6 at/ion, are practically independent of the grain size of copper, the thickness of the sputtered layer, and the irradiation fluence. Calculations using the SRIM program show that, when taking into account the redeposition of atoms from the walls of the cones, the sputtering yield of a cone-shaped copper relief Y_c is 3.5 times less than the sputtering yield of a single cone, 1.2 times greater than the sputtering yield of a smooth surface, and the value of 9.25 at/ion is close to the experimentally measured one.

We propose a model for a low-current gas discharge in a mixture of argon and mercury vapor in the presence of a thin dielectric film on the surface of a cathode. The model takes into account that in such a mixture, a significant contribution to ionization of the working gas can be made by the ionization of mercury atoms during their collisions with metastable excited argon atoms. Positive charges accumulate in the discharge on the surface of the film, creating an electric field in the dielectric sufficient to induce field electron emission from the metal substrate of the electrode into the dielectric. These electrons are accelerated in the film by an electric field and can exit it into the discharge volume. This increases the effective ion–electron emission yield of the cathode. The temperature dependences of the discharge characteristics show that due to a rapid decrease in the concentration of mercury vapor in the mixture with decreasing temperature, the electric-field strength in the discharge gap and the discharge voltage increase. The presence of a thin dielectric film on the cathode can improve its emission properties and significantly decrease the discharge voltage. These phenomena result in a decrease in the energy of ions and atoms bombarding the cathode surface and, consequently, a reduction in the intensity of cathode sputtering in the discharge.

Layered composite materials based on niobium and cermet are produced via the self-propagating high-temperature synthesis of preliminarily structured samples using metal foils (Ti, Nb, Ta, Ni) and reaction tapes (Ti + 1.7B) and (5Ti + 3Si). The reaction tapes for synthesis are produced by rolling powder mixtures. The microstructure, and elemental and phase compositions of the synthesized multilayer composite materials are studied by scanning electron microscopy and X-ray phase analysis. Particular attention is paid to the formation of intermediate layers and surface modification occurring during combustion. The strength characteristics of the synthesized materials are determined according to the three-point loading scheme at temperatures of 1100°C. Analysis of the obtained materials shows that joining in the combustion mode of metal foils and reaction tapes is provided due to reaction diffusion, mutual impregnation, and chemical reactions occurring in the reaction tapes and on the surface of the metal foils. The formation of thin intermediate layers in the form of cermet and eutectic solutions provides the synthesized multilayer materials with good strength properties up to 87 MPa at 1100°C. These results are of interest for the development of structural materials operating under extreme conditions.

Within the framework of a new approach to the problem of calculating the total energy of a diatomic molecule in first-order perturbation theory, it is shown that the potential-energy screening function is a solution to a diffusion-type equation in which the role of a time variable is played by the mean square of the amplitude of collective oscillations of electrons per degree of freedom. The total energy of a diatomic nitrogen molecule in the ground and excited states is calculated in first-order perturbation theory using tabulated eigenfunctions and eigenvalues of the energy of isolated atoms, which approximate solutions of the Hartree–Fock equation. The reliability of the numerical method for calculating the total energy of a diatomic nitrogen molecule in first-order perturbation theory is verified using an exact solution with an atomic form factor for the screened Coulomb potential. The new approach to the problem of calculating the total energy of a diatomic molecule in first-order perturbation theory does not contain free parameters, but is based on the numerical solution of a system of nonlinear equations.

Using Kerr microscopy, the effect of temperature on the displacement of domain boundaries in ultrathin exchange-coupled ferromagnetic layers in heterophase Pt/Co/Pt/Co/Pt films with perpendicular magnetic anisotropy and a nonmagnetic wedge-shaped spacer layer is experimentally studied. The exchange interaction between the Co layers is investigated for spacer-layer thicknesses ranging from 5 to 6 nm within the temperature range of 200 to 300 K. The independent displacement of domain boundaries in the Co layers under the action of a perpendicular magnetic field applied to the sample surface occurs within the range of thicknesses d₀ < d < d_CR. Throughout the entire temperature range, the displacement of domain boundaries along the Pt wedge results in their stabilization in an equilibrium position. This position depends on the magnitude of the applied field, the thickness of the nonmagnetic spacer layer, and temperature. It is determined by the balance of forces acting on the boundary, including the external field, the effective exchange field between the Co layers, and the coercivity field. Upon the removal of the external field, the domain boundaries relax to the initial state with d = d₀ due to the effect of the exchange field. The characteristics of this relaxation depend on the temperature. The study of the mechanism of domain-boundary stabilization near d_CR reveal that the critical thickness of the nonmagnetic spacer layer d_CR and the coercivity field exhibit oppositely directed dependences on temperature.

The study of the fractal properties of the surface of Nd_{100 – x}Fe_x alloys in a wide range of concentrations х (х = 20–90) was carried out in the framework of the fractal thermodynamics model. To this end, we performed an analysis of scanning electron microscopy images of the surfaces of a series of Nd_{100 – x}Fe_x alloys synthesized by induction melting. A high degree of proximity of the surface structure of all the studied samples, both before and after etching, to fractals is shown. The values of the parameter δ characterizing the relative deviation of the studied samples from the fractal are in the range of 0.017–0.029. Three-dimensional diagrams of the fractal parameters S_f, T_f, E_f, and x and two-dimensional diagrams of the same parameters S_f, T_f, E_f, and x reflecting the nature of the state of the surfaces of Nd_{100 – x}Fe_x alloy samples before and after etching are constructed. For all investigated alloy samples, the values of the parameters of the fractal equations of state are calculated. The correlation of the maximum value of the coercive force H_c = 4.8 kE with the values of fractal entropy S_f = 39.86, fractal temperature T_f = 529, and fractal dimension D = 2.6530 of the Nd_{100 – x}Fe_x alloys at x = 20 has been established.