The process of nonstationary diffusion of nonequilibrium minority charge carriers occurring after the termination of electron-beam irradiation of a semiconductor target is considered. Mathematical models of three-dimensional diffusion of charge carriers generated by an electron beam with energies up to 50 keV in a homogeneous semiconductor material were investigated for the cases of one or two independent recombination channels. Model calculations were performed for the diffusion of excitons in homogeneous single-crystal gallium nitride.
Using scanning electron and atomic force microscopy and nano- and microhardness testing, we studied the mechanism of the influence of two types of dynamic impacts (explosive and high-voltage nanosecond electromagnetic pulses) on the morphology and structural and mechanical properties of the surface of rocks (granite, quartzite, coal) and rock-forming minerals (dolomite, calcite, quartz). The advantages of using the mechanical (shock-wave) action of an explosion in the processes of rock softening and the nonthermal effect of high-power electromagnetic pulses to increase the selectivity of liberating mineral intergrowths during the processing of refractory mineral raw materials are shown.
Using dielectric spectroscopy (DS), this study investigated the characteristics of polarization processes in copper-doped nanocrystalline silver iodide films in the region of the thermal superionic phase transition. It was found that doping with copper (5 vol
The surface changes of dielectric melamine-formaldehyde (MF-R) microparticles placed in a direct current gas discharge plasma were studied. The microparticles became part of a stable plasma-dust structure and were exposed to the plasma. A stratified glow discharge in an inert gas at a pressure of 0.4 mm Hg was maintained in the discharge chamber and a discharge current of i = 2.5 mA. Using a proven method of injecting and extracting dust particles after the discharge was turned off, the material was collected to study changes in the surface of particles that had been in plasma-dust traps. MF-R particles were monodisperse spheres with a diameter of (7.3 ± 0.4) μm and a density of 1.5 g/cm3. They were exposed to plasma for periods ranging from 5 to 25 min. The particle size and surface texture changed over time. The surface Merlin scanning electron microscope images of the microparticles were observed using a Merlin scanning electron microscope. Image analysis was performed using ImageJ and the FracLac 2.5 add-on module.
The destruction and change of elemental composition of surface layers of an AlN thin film deposited by reactive magnetron sputtering on a glass ceramic substrate (including metal sublayer) under the influence of high-power ion beam of nanosecond duration have been investigated. The spatial characteristics of the surface destruction of the film have been determined. Cracking of the film, as well as partial or complete removal of fragments of film destruction, is observed depending on the beam current density. The effect of a high-power ion beam on the systems AlN thin film‒Al thin film‒glass ceramic and Al thin film‒AlN thin film‒Al thin film‒glass ceramic was considered. The formation of aluminum droplets on the surface of glass ceramic in the areas of the removed Al film, as well as on the surface of fragments of AlN film destruction at a single irradiation with a high-power ion beam with current density up to 150 A/cm2 was found. The depletion of the surface layer of the film by nitrogen was established. Possible mechanisms for the observed changes in the surface layer of AlN thin film are discussed.
The human body primarily comprises spontaneously organized polymers like proteins and ceramic materials such as bone minerals. Additionally, trace elements in the form of metals play pivotal roles at the molecular level. Simultaneously, metals and their alloys serve as crucial structural materials for surgical implants, particularly in orthopedics, and their application has recently expanded to other tissues like blood vessels. However, the increased usage of metal implants in medicine has brought about challenges related to their limited lifespan. Metallic biomaterials encompass a variety of alloys: stainless steels, magnesium, titanium, cobalt, nickel-titanium shape memory alloys, as well as tantalum, silver, and zirconium. This review primarily focuses on titanium-based biomaterials, emphasizing critical issues concerning their clinical application. These issues encompass bone integration in porous or structured implants, joint prostheses wear, surface modification of scaffolds and implants, the general toxicity of metal ions released during corrosion, phase composition of titanium-based alloys, and fatigue failure of structures due to repetitive mechanical stress, particularly corrosion fatigue. In conclusion, the review underscores the most significant challenges associated with titanium-based biomaterials, while also highlighting the most promising approaches and strategies to address them.
Transparent conductive indium tin oxide films are used in aerospace technology as conductive layers of dielectric thermal control coatings and protective glasses of solar batteries. The electrical conductivity of the surface prevents its differential electrification under the influence of charged particle flows in the Earth’s atmosphere. At the same time, the effect of space factors, including the incident flow of atomic oxygen during flight, on electrical conductivity has not been studied. In this paper, we study transparent conductive indium tin oxide coatings deposited on glass and polyimide film substrates. The effect of the incident flow of atomic oxygen was simulated by irradiating the samples with an oxygen plasma flow. The equivalent fluence of the atomic oxygen, determined by the mass loss of a polyimide film witness sample, served as a measure of the effect. Experiments have shown the effect of a 100‒3000-fold drop in the electrical conductivity of the coating as the equivalent fluence of atomic oxygen increases to 9 × 1021 cm–2. Analysis of the dependence of resistance on fluence has shown that the supposed sputtering of the coating under the influence of the plasma flow is not the dominant mechanism. The probable cause of the degradation of electrical conductivity should be sought in the change in the bulk properties of the semiconductor material.
Using small-angle neutron scattering (SANS) a nanoporous material–nonwetting liquid system was studied at pressures up to 600 bar. A mixture of heavy and light water was used to reduce the contrast between the material and liquid. The pores filling with liquid with increasing pressure, as well as the liquid outflow (or its absence) with decreasing pressure, were studied. The material pore sizes were determined, and it was shown that the pore size is not smooth.
The influence of the nearest atomic surrounding on the sputtering of atoms from the surface of (001) Au face in the 〈010〉 azimuthal direction toward the Wehner spot is examined. Using the molecular dynamics method, the ejection of an atom from a surface lattice site toward a lens consisting of two nearest neighbor surface atoms was calculated, taking into account varying numbers of surrounding atoms: 4 or 20 atoms from one top layer and 8 or 16 atoms from two top layers. Due to the above-surface scattering effect, as the atomic surrounding expands, the sputtering yield increases by 17 to 37
The motion of charged particles in a crystal can be either regular or chaotic. At the quantum level, chaotic behavior manifests in the statistical properties of an ensemble of energy levels. Systems in which regions of regular motion in phase space are separated by a domain of dynamical chaos are of particular interest. The level statistics in such systems are strongly influenced by the possibility of tunneling between dynamically isolated regions of phase space. Accounting for this effect leads to the Podolsky–Narimanov distribution function. This article presents an analysis of the dynamics of transverse motion of high-energy positrons (40–50 GeV) channeling along the [100] direction of a silicon crystal. The parameters of the Podolsky–Narimanov distribution are determined. It is shown that the Podolsky–Narimanov distribution describes the statistics of nearest-neighbor energy level spacings of transverse motion more accurately than known alternatives.
To investigate radiation-induced damage, Fe ions with an energy of 5.6 MeV and a fluence of 1015 cm–2 were implanted into two iron oxides: hematite Fe2O3 and magnetite Fe3O4. Conversion electron Mössbauer spectra, Raman spectra, and data from electron and atomic force microscopy were obtained for the irradiated surfaces, as well as after removal of a surface layer with a thickness of 1 μm. Irradiation affected the Mössbauer spectra of hematite and magnetite in different ways. In hematite, an additional H2 sextet was formed, corresponding to defect Fe sites. In magnetite, irradiation caused only line broadening of the B sextet. The study concludes that the spinel structure of Fe3O4 is more resistant to irradiation effects. In the center of the Mössbauer spectra of both oxides, quadrupole doublets corresponding to the Fe2+ phase were observed before polishing. The formation of this phase is interpreted within the thermal spike model as a result of material quenching in the ion track region. According to electron and atomic force microscopy data, after polishing to a depth of approximately 1 μm, a sharp increase in surface roughness was observed, with the formation of pits up to 300 nm deep. The destruction of the subsurface layer is evidently caused by a high concentration of radiation-induced defects, which form regions of large stress, leading to crack formation and loss of layer continuity.
The transition radiation of a charged particle in the simplest case of its incidence on the infinite perfectly conducting plane can be described using the method of images known from electrostatics. The same method allows one to find the spatial field distribution in some more complicated cases. The present paper describes the transition radiation from the bunch of nonrelativistic charged particles incident on the target consisting of two conducting half-planes that make rectangular dihedral angle (when the incidence takes the place from the inner side of the angle). The presence of interference maxima and minima in the angular distribution of the radiation makes it possible to relatively easily estimate the main characteristics of the bunch: the impact parameter of its center and the charge density form factor. The results can be used to improve the methods of diagnostics of charge particles beams.
A comparative analysis was performed of the diffuse reflectance spectra and their changes after irradiation with 100 keV protons of TiO2/SiO2 bilayer hollow particles. The intensity of radiation-induced absorption bands in hollow TiO2/SiO2 particles is lower than that in TiO2 microparticles. The enhanced radiation resistance effect of TiO2/SiO2 bilayer hollow particles may be attributed to the high specific surface area of the particles, which serves as a sink for radiation defects, as well as to the presence of a protective amorphous SiO2 layer on the surface of TiO2 microspheres, which leads to a lower concentration of absorption centers in TiO2 responsible for absorption in the visible spectral range.
This study reports the synthesis and structural characterization of two equimolar high-entropy alloys, TiVCrNbCo and TiVCrNbZr, which are promising hydrogen storage materials. The alloys were produced via vacuum arc melting of elemental powders under an argon atmosphere; then their phase composition and microstructure were characterized using X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS), both before and after hydrogen decrepitation (HD process). The TiVCrNbCo alloy predominantly crystallizes in the hexagonal Laves C14 phase, whereas the TiVCrNbZr alloy forms a structure consisting whereas the TiVCrNbZr alloy forms a structure consisting of mixtures of cubic Laves C15 and body-centered cubic (BCC) phases. Hydrogen process transforms both alloys into finely dispersed powders, leaving residual hydrogen contents of 0.19 wt
The present study is devoted to a new technique for creating diffraction gratings based on nanoporous Ge (PGe) layers by irradiating a smooth single-crystal c-Ge (Bi:PGe) substrate with Bi++ ions through a copper mesh mask at an energy of E = 72 keV, an ion beam current density of J = 5 μA/cm2, and a fluence D range from 1.3 × 1015 to 1.3 × 1017 ion/cm2 with the ILU-3 ion accelerator. Morphological and elemental analyses of the Bi:PGe surface for different D values were performed using a high-resolution scanning electron microscope. At D = 1.3 × 1015 ion/cm2, the formation of a porous fraction in the form of vertical honeycombs with nm-sized round holes was detected. When the critical value D = 3.1 × 1015 ion/cm2 is exceeded, a spongy porous structure consisting of intertwining nanowires appears, accompanied by swelling of the Bi:PGe layer instead of the expected sputtering of the c-Ge surface. With increasing D, the nanowires become thinner and the free volume between them increases. The formation of periodic Bi:PGe microstructures on the c-Ge surface was monitored using optical and probe microscopy. The efficiency of the optical diffraction grating was demonstrated by probing it with He–Ne laser radiation.
Tungsten is widely considered one of the key candidate materials for the first wall of fusion reactors due to its favorable thermophysical properties. However, its radiation resistance is largely determined by the behavior of point defects, particularly vacancies, especially at high temperatures. In this work, an atomistic study of the thermodynamic and diffusion characteristics of vacancies in tungsten was carried out. The modeling approach combines a modified molecular statics method (MMSM) with molecular dynamics (MD) within the framework of a natural thermostat model. The calculations were performed using the EAM potential. It was found that, starting from the 11th coordination sphere, atomic displacements around the vacancy exhibit a temperature dependence consistent with that of the lattice parameter. Based on this, temperature dependences of vacancy formation energy and formation volume were determined. Additionally, vacancy migration was simulated, allowing for the calculation of the vacancy diffusion coefficient over a wide temperature range. The results provide critical input for modeling defect evolution mechanisms under radiation damage and high-temperatures conditions.
The motion of fast charged particle (electron or positron) through a single crystal along densely packed crystallographic planes can be adequately described as a motion in a periodic averaged smooth potential formed as a sum of potentials of parallel atomic planes. Here we consider the motion of particles with transverse energies ε еU0 close to the energy of potential barriers separating planar potential channels. Such motion is characterized by the possibility to move from one channel to another, as well as by the band quantum structure of allowed values of transverse energy. It is demonstrated that characteristics of motion, as well as parameters of accompanying electromagnetic radiation, are changing with a gap when a particle changes transverse energy from under-barrier level ε < еU0 to over-barrier level ε > еU0. Namely, the direction of particle drift in crystal deviates from the direction of channels and the frequency of its oscillations doubles. Simultaneously, the amplitude of deviations from the average drift direction decreases multiple times. As the result, the frequency of electromagnetic radiation emitted by the particle doubles and its intensity decreases abruptly. With further growth of transverse energy, the amplitude of oscillations decreases further, the frequencies of radiation emitted by the particle increase, but its intensity decreases.
The emission and fragmentation of iron-carbon clusters under bombardment of interfaces of pyrolytic graphite samples with a Fe target by Cs+ ions with an energy of 18.5 keV were studied. It was found that, along with clusters FeC_n^ - and Fe_2C_n^ - , effective generation of cesium-containing clusters FeCsC_n^ - and Fe_2CsC_n^ - was observed. A conclusion has been made about the prospects of using the ion sputtering technique for generating clusters of different sizes and stoichiometry.
High-pressure cells designed for studies of condensed matter using several neutron scattering techniques, including diffraction, spectroscopy, and small-angle neutron scattering, are discussed. A key factor for an efficient neutron experiment is minimizing the self-shielding effect caused by cell materials while maintaining the required pressure and sample volume. Clamp pressure cells based on nonmagnetic high-hardness alloys with operating pressures up to 3.5 GPa are considered. Optimization of the geometry of high-pressure cells with different angular apertures of the outgoing neutron beam was carried out. The main result of this study is the identified dependence of critical pressure on the opening angle of the neutron beam scattered by the sample.
A model of a glow gas discharge in a mixture of argon and mercury vapor is formulated in the presence of a thin insulating film on the cathode surface. Dependences of the discharge characteristics on the mixture temperature are calculated in the range of its variation, in which a noticeable contribution to ionization of the working gas is made by the ionization of mercury atoms by metastable excited argon atoms (the Penning reaction). It is shown that in the case of a cathode without an insulating film when the temperature increases until the relative mercury content in the mixture reaches 5 × 10–3, a reduction of the electric field strength in the discharge cathode layer takes place due to an increase of the mixture ionization coefficient. A further increase of the temperature, due to growing mercury content in the mixture and a decrease in the contribution of the Penning reaction to the mixture ionization coefficient, results in its reduction, followed by an increase of the electric field strength. At the existence of an insulating film on the cathode a contribution to its effective electron emission coefficient, along with the ion-electron emission, is also made by the temperature-enhanced field electron emission from the cathode metal substrate into the insulating film, caused by the existence of a strong electric field in it. As a result of the increase in temperature, the cathode effective ion-electron emission coefficient decreases due to a reduction in the discharge current density. This leads to a smaller decrease in the electric field strength in the discharge cathode layer than that in case of a cathode without a film, only in a small interval of cathode temperature variation. Therefore, the cathode without an insulating film under its heating in glow discharge is sputtered more intensively than the cathode with the film, which results in a shorter service life of lamps with such cathodes.
