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

The fracture and change in the elemental composition of the surface layers of aluminum nitride ceramics under the action of a high-power ion beam of nanosecond duration have been studied. The spatial characteristics of ceramics surface fracture have been determined. The destruction occurs mainly along the boundaries of particles (crystallites) from which the ceramics is sintered. Complete removal of some of these particles from the surface layer is observed both after single and multiple irradiations with a current density of 150 A/cm². The formation of hemispherical droplets of various sizes is detected both on the irradiated surface of the ceramics and on the surface after removal of the fracture fragment (after multiple irradiation). Depletion of the surface layer of the ceramics in nitrogen has been established. Possible mechanisms of the observed changes in the surface layer of the ceramics are discussed.

The energy spectra and average energies of sputtered atoms were calculated for a number of amorphous targets (Si, Ti, Ni, V, and Nb) bombarded with 1 keV Ar ions. The calculations were carried out using the computer simulation programs OKSANA and SRIM-2013. It was shown that for targets whose atoms are heavier than incident ions, SRIM can greatly overestimate the contribution of fast sputtered atoms. This is especially noticeable in calculations with the surface binding energy found by adjusting the calculated sputtering yields to the experimental ones. The simulation results are compared with analytical estimates of the average energy of ejected atoms based on the linear theory of sputtering. It was found that in all the cases considered, these estimates are also greatly overestimated, since they do not take into account the degradation of collision cascades at low bombarding energies. A good agreement of the OKSANA, TRIM.SP, and ACAT simulations is noted.

Results of a study of the effect of X-rays of 100 kR/h on the structure, tribological and elastic properties of elastomers based on nitrile-butadiene rubber with degrees of vulcanization of t₇₀ and t₉₀ are presented. It is found that irradiation of rubber with an exposure dose up to 50 kR leads to an increase in the elongation at break and tensile strength due to a decrease in the degree of crystallinity and to an increase in the crosslink density and a decrease in the specific volume of the polymers. It is obtained that the X-ray irradiation of rubber with exposure doses in the range from 50 to 100 kR leads to an increase in a degree of crystallinity and to deterioration in elastic-strength properties of rubber. It is suggested that the crosslinks of elastomers based on nitrile-butadiene rubber break after the X-ray exposure of dose in the range from 50 to 100 kR. The established nonlinear dependences of the elastic-strength properties of nitrile butadiene rubber with degrees of vulcanization t₇₀ and t₉₀ from an exposure dose point to greatly depending of the rubber intermolecular crosslinks density from an exposure dose of the X-ray and time after exposure. It is obtained a radiation aging of NBR elastomers have been exposure with X-ray. It is established that 2 months after irradiation the elongation at break decreases for NBR elastomers samples and the coefficient of dynamic friction decreases at first and increases after a month.

Images of the distribution of microfocus bremsstrahlung from a new source based on an 18 MeV betatron, which has passed a 0.4 mm thick steel plate with a 1.2 mm wide sharp edge, are presented. The photographs demonstrate an anomaly in the interaction between the microfocus bremsstrahlung and the plate tip in the form of a narrow dark stripe along the tip image, which indicates an increase in the radiation intensity in this area. The dark stripe provides a contrast in the tip image, which, together with the high sharpness due to the microfocus of the source, allows the tip position to be visualized with high precision. The dark stripe in the images was not observed when using radiation from 450 and 45 keV X-ray tubes with foci of 400 and 100 µm. The absorption of radiation ensures a smooth change in the blackening of the sharp edge and blurring of the tip in the image due to the size of the radiation source. The observed effect with microfocus radiation of the new source is determined by the scattering of radiation by the tip with the possible participation of wave effects, which needs to be further investigated.

To explain the increased yield of positive particles from the surface of a positively charged dielectric, a computer simulation was performed using the density functional theory. The model system was a fragment of a Teflon molecule (CF₂) in a vacuum. The binding energy of atoms in this system in the neutral state (without removing electrons from the system) was calculated, after which a similar calculation was performed for an ionized fragment of the Teflon molecule (with the removal of one electron from the system of atoms). The calculations showed that the energy of complete dissociation of one fragment of the Teflon molecule in the neutral state is 11.02 eV, which agrees with the experimental data with good accuracy. The binding energy in the ionized fragment of the molecule is 2.86 eV, while the Teflon molecule fragment dissociates into a neutrally charged fluorine atom and a positively charged CF fragment. In calculations taking into account the dipole moment of the Teflon molecule fragment, the binding energy was equal to –2.75 eV, and the Teflon molecule fragment also dissociated into a neutral fluorine atom and a positively charged CF fragment. The obtained results may be the reason for the increased release of positive particles from the surface of a positively charged massive dielectric.

The relevance of the work is associated with the widespread use of high-temperature heaters in industry. A promising method for producing such heaters is self-propagating high-temperature synthesis (SHS). MAX phases, which combine the properties of metals and ceramics, are resistant to oxidation in air at high temperatures, are not afraid of thermal shocks and are promising for the production of high-temperature heaters. The aim of this work was to study the possibility of producing conductive coatings based on the MAX phase Ti₂AlC by the SHS method in the self-propagating mode and in the “thermal explosion” mode. For this purpose, layers of Ti, Al, C powders and Ti + C, 2Ti + Al mixtures in various combinations were applied to the substrate. In the self-propagating mode, the reaction was initiated using a Ti + 2 B mixture and an electric coil. In the thermal explosion mode, the samples were heated with a linear change in the furnace temperature and the temperature of the powder layers was recorded. Anomalously low reaction initiation temperatures were recorded. It has been suggested that this may be due to the oxidation of the mixture components in air and the transition of the process from the thermal explosion mode to the ignition mode. Samples with high electrical conductivity have been obtained, which can be used as electric heaters.

The development of biodegradable composite materials is crucial for advancing temporary medical implants. Ultrafine-grained (UFG) magnesium alloys, despite their excellent mechanical properties and biocompatibility, suffer from rapid corrosion in physiological environments. To improve this issue, we applied surface plasma modifications by first depositing strontium-doped calcium phosphate (Sr-CaP) coatings using Micro-arc oxidation method to improve osteointegration and provide initial corrosion protection followed by a zirconium dioxide (ZrO₂) top layer deposited using an RF magnetron sputtering, which further enhanced the corrosion resistance and mechanical stability of the system. The dual-layered Sr-CaP/ZrO₂ system showed a significant improvement in corrosion resistance, with a reduction in corrosion current density by several orders of magnitude and polarization resistance reaching up to 2.3 × 10⁷ Ohm cm². Optimized deposition parameters ensured the formation of a uniform ZrO₂ coating with a poorly crystalline monoclinic phase and high residual stresses, contributing to the enhanced protective properties, however still providing biodegradation possibility. This multilayered coating system provides a promising surface modification strategy for controlling the degradation rate of UFG magnesium alloys, making them suitable for use in temporary biomedical implants such as orthopedic devices.

By thermal decomposition of nickel carboxylate and zinc carboxylate based on substituted aromatic acids, nickel oxide and zinc oxide nanoparticles were obtained, respectively. It was shown that the shape of nickel oxide nanoparticles is spherical with a particle size of up to 55 nm and the shape of zinc oxide nanoparticles is close to pyramidal with sizes of up to 60 nm. It was proven that the introduction of nickel oxide nanoparticles with a concentration of 0.05% into industrial oil as an additive increases the antiwear properties of the friction surface by 25% and zinc oxide nanoparticles with a concentration of 0.025% increases the antiwear properties of the friction surface by 20%.

Xenon ions with energies of 5 and 8 keV are used to amorphize a single-crystal silicon substrate. Cross-sectional samples of the irradiated areas are examined by transmission electron microscopy in the bright-field mode, and the thicknesses of the amorphized layers are determined based on analysis of the obtained images. The ion-bombardment process is modeled using the Monte Carlo method along with the critical point defect density model, which makes it possible to obtain theoretical estimates of the thickness of these layers. The calculation results are compared with experimental data. It is shown that Monte Carlo simulation describes the low-energy xenon-ion-induced amorphization of single-crystal silicon with acceptable precision.

The work proposes a mechanism for the formation of a layered structure of metal nanoparticles in dielectrics irradiated with fast electrons. On the example of silver-containing glass, a model is discussed in which silver nanoparticles can accumulate under the surface in two layers: wide, at the depth of embedded primary electrons (~3 μm for 30 keV), and extremely narrow ~0.1 µm, closer to the surface (at a depth of ~0.5 μm). Both the first and second layers are due to strong electrostatic fields arising in the regions of embedded electrons (space negative charge) and near-surface positive space charge formed by true secondary electron emission. The process of diffusion of polarized silver atoms in the specified inhomogeneous electric field with a secondary electron emission coefficient greater than unity is considered. In the presented model of the distribution of space charge and electric field in silver-containing glass irradiated with fast electrons, an equilibrium profile of the concentration of silver atoms in the near-surface layer is obtained. It is shown that in the formed electric fields it is possible to form a structure with areas of enrichment and depletion of the specified impurity. The calculated values of the equilibrium concentrations of silver atoms at the surface may exceed the corresponding volume values by several times.