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

The change of polytetrafluoroethylene surface properties under the influence of nonthermal nonequilibrium plasma generated by plasma jets at atmospheric pressure is shown. The unsteady form of diffuse discharge, a glow discharge, which is superimposed on weak-current spark discharges, is experimentally realized and formed in the gas flow in the form of atmospheric pressure plasma jets. The plasma jet (diameter of the plasma jet is 2.5 cm, length of the jet is 1–2 cm) is oriented perpendicularly to the surface of polytetrafluoroethylene. Water contact angle measurements and electron microscopy are used to determine the surface characteristics of the material. An intensive and homogeneous improvement of the polymer surface wettability is observed on a large area (contact area S ≈ 7 cm²) subjected to plasma treatment during the first seconds of exposure to the plasma jet. The contact angle of the original polytetrafluoroethylene with a drop of water is 102°, while the contact angle θ decreases to 65° when exposed to plasma jets. In the area of plasma jets impact at atmospheric pressure, in contrast to the original surface, there are pronounced inhomogeneous surface formations, and at the interface a sharp change in the wettability of the surface is observed. On the surface of polytetrafluoroethylene sample in the area of plasma jets impact, the percentage of carbon increases, while the percentage of fluorine decreases.

An experimental study of the effect of high-current electron beams on crystals made of polycrystalline tungsten and corrosion-resistant ferritic-martensitic steel EK-181 was carried out, as well as a numerical simulation of the process of interaction of the beam with the target, in which the energy of the electron beam was absorbed in the near-surface layers of the samples under study. The experiments were carried out on the Kalmar high-current electron accelerator at an average pulse energy of E ≈ 100 ± 20 J (pulse duration at half maximum 100 ns). During the experiments, samples were irradiated from one to ten times. Numerical modeling was performed using electron spectra calculated on the basis of data (currents and voltages in the diode gap) obtained as a result of electrical measurements. The difference in the nature of destruction of tungsten and steel was demonstrated. It has been shown that tungsten begins to crack after three-pulse exposure with an energy of about 100 J, which correlates well with tests on other types of installations. On steel, minor cracking was observed only after 8–10 pulses of exposure. Numerous traces of droplets of melting and redeposition of the target material were found on the surface of the steel target. For both materials, the specific amount of energy absorbed in the region of interaction of the electron beam with the target was estimated.

The structure of the side surfaces of the bulk Zr₆₂Cu₂₂Fe₆Al₁₀ amorphous alloy before and after compressive deformation at room temperature was studied using X-ray diffraction and scanning electron microscopy (SEM) methods. After preparation, the samples of the amorphous alloy had a square cross section of 5 × 5 mm and a length of 40 mm. Examining the side surfaces of the samples allows one to avoid influencing the surface structure of a tool used for deformation. The plastic deformation of amorphous alloys occurs through the formation and propagation of shear bands. During compressive deformation at room temperature, a system of steps was formed on the end surfaces of the sample caused by shear bands coming to the surface. Steps on surfaces have different sizes (thickness and height). It was established that the structure of large steps is complex: they consist of elementary steps 15–30 nm thick. The local deformation was estimated based on the size of the steps. The formation of a small number of nanocrystals during deformation was discovered. The nanocrystals are approximately 10 nm in size. The results obtained open a new direction for research into the structure of deformed amorphous alloys and nanocrystallization processes under the influence of deformation.

The preparation of coating layers containing the borides Cr₂B, Cr₂B₃, and FeB on Kh12MF steel using the electron-beam treatment of reacting coatings made of Cr₂O₃, amorphous boron, and carbon is considered. The influence of the treatment time on the structure, composition, and microhardness of the layers is investigated. The maximum microhardness of the layers is ~18.5 GPa. The studies allow one to conclude that electron-beam treatment can be used to strengthen cutting and other tools, which experience high temperature heating during operation, without a significant reduction in performance. It is known that, along with high hardness and wear resistance, boride layers also have a significant disadvantage: increased brittleness. The studies carried out show that the use of electronic heating allows a reduction in brittleness and increase in plasticity of the alloys. The layers after electron-beam boriding have a heterogeneous structure combining hard (brittle) and more plastic structural components.

This study examines the differences in the crystallization kinetics of the free and contact sides of an Fe₇₇Ni₁Si₉B₁₃ amorphous-alloy ribbon at 400°C. X-ray phase analysis reveals that crystals based on α-Fe form on the contact side after just 5 min of annealing. In contrast, on the free side, reflections corresponding to α-Fe crystals are only detectable after 30 min of annealing. The relative content of the crystalline phase is determined using X-ray diffraction data, based on the relationship between the integral intensity of the reflection of the analyzed phase and its volume fraction. We explore the possible reasons for the observed differences in crystallization. Crystallization in the surface layers of both the contact and free sides of the ribbon occurs in two stages: the isotropic growth of existing nuclei with a decreasing rate of crystal formation, followed by the slowed anisotropic growth of already formed crystals. The first stage is satisfactorily described by the Johnson–Mehl–Avrami–Kolmogorov (JMAK) thermodynamic formalism, whereas applying a kinetic equation to describe the second stage is not appropriate.

A nanocomposite of zinc oxide doped with nickel oxide (NiO/ZnO) may enhance the electrochemical characteristics of capacitors .This work evaluates the facile sol-gel, solid state, and thermal hydrolysis procedures for producing NiO/ZnO nanoparticles. X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM) were used to examine the impact of the synthesis methods on the structural, functional, and morphological characteristics of NiO/ZnO products. The thermal hydrolysis method confirmed the high purity of NiO/ZnO peaks. The FTIR studies were adopted for the purpose of establishing the M–O groups, and morphological analyses were conducted to determine the thermal hydrolysis methods results. The results showed that NiO/ZnO nanocomposites made by hydrothermal technique might be used as possible electrode materials for high-efficiency super capacitors.

A method is proposed for calculating the component composition and thickness of a layer of two-component targets changed as a result of prolonged (stoichiometric) sputtering when irradiated with light ions. The method is based on a previously tested model of sputtering inhomogeneous two–component materials with light ions. In the case of stationary sputtering of tungsten and tantalum carbides with helium ions, the results of calculations of the component composition and thickness of the modified layer are presented in comparison with experimental data.

The effect of high-temperature electron and proton irradiation on the characteristics of devices based on SiC has been studied. For the study, industrial 4H-SiC integrated Schottky diodes with an n-type base with a blocking voltage of 600, 1200, and 1700 V manufactured by CREE are used. Irradiation is carried out by electrons with an energy of 0.9 MeV and protons with an energy of 15 MeV. It is found that the radiation resistance of SiC Schottky diodes under high-temperature irradiation significantly exceeds the resistance of diodes under irradiation at room temperature. It is shown that this effect arises due to the annealing of compensating radiation defects under high-temperature irradiation. It is revealed that this effect arises due to the annealing of compensating radiation defects under high-temperature irradiation. The parameters of radiation defects are determined by the method of transient capacitance spectroscopy. Under high-temperature (“hot”) irradiation, the spectrum of radiation-induced defects introduced into SiC differs significantly from the spectrum of defects introduced at room temperature. The radiation resistance of silicon and silicon carbide is compared. The relatively small difference in the rate of carrier removal in SiC and Si upon irradiation at room temperature is due to the fact that in SiC, in contrast to Si, there is practically no annealing of primary radiation defects during irradiation.

Methods of modifying surface and near-surface layers of materials and coatings by ion beams can be applied in many fields of science and technology. To practically implement the technologies for the targeted improvement of the performance properties of parts and products for various purposes, it is of great interest to develop the methods of deep ion doping of near-surface layers of semiconductor materials, as well as metals and alloys due to the enhancement of radiation-stimulated diffusion under conditions when the irradiated sample deep layers are not subject to a significant temperature impact. This study concerns features and regularities of implementing the synergy of high-intensity titanium ion implantation at current densities of several hundred mA/cm² with simultaneous energy impact of a submillisecond ion beam with a power density reaching several tens of kW/cm² on the surface. This work is the first to show that the synergy of high-intensity ion implantation and the energy impact of a high-power density ion beam, taking titanium implantation into silicon as an example, provides the possibility of increasing the ion doping depth from fractions of μm to 6 μm by increasing the irradiation time from 0.5 to 60 min.

Anomalous diffusion is a random process in which the root-mean-square displacement of a particle from the starting point depends nonlinearly on time. The possibility of such behavior for high-energy particles moving through the crystal under conditions close to axial channeling was found earlier. In this case, the rapid displacement of particles in a plane transverse to atomic strings (Lévi flights) is due to the temporary capture of the particles in planar channels. In this work, the anomalous diffusion exponent has been found by numerical simulation for different values of the energy of electron transverse motion in the (100) plane of a silicon crystal. It has been shown that, in the case of electrons with an energy exceeding by 1 eV the height of the saddle point of the potential of a system of atomic chains [100], the results are consistent with those obtained earlier. It has been confirmed that the anomalous nature of diffusion is due to the possibility of short-term capture of particles in planar channels. With increasing transverse energy, this possibility disappears and the diffusion becomes normal (Brownian).