Том 12, № 4 (2018)

To study spin-dependent transport phenomena in Fe₃Si/p-Si structures we fabricated 3-terminal planar microdevices and metal/semiconductor diode using conventional photolithography and wet chemical etching. I‒V curve of prepared diode demonstrates rectifying behavior, which indicates the presence of Schottky barrier in Fe₃Si/p-Si interface. Calculated Schottky barrier height is 0.57 eV, which can provide necessary conditions for spin accumulation in p-Si. Indeed, in 3-terminal planar device with Fe₃Si/p-Si Schottky contact Hanle effect was observed. By the analysis of Hanle curves spin lifetime spin diffusion length in p-Si were calculated, which are 145 ps and 405 nm, respectively (at T = 300 K). Spin lifetime strongly depends on temperature which can be related to the fact that spin-dependent transport in our device is realized via the surface states. This gives a perspective of creation of spintronic devices based on metal/semiconductor structure without need for forming tunnel or Schottky tunnel contact.

The principles of designing a subcritical neutron-multiplying system with reactivity modulation, which can be used as the target in a superbooster with a linear proton accelerator, are described. Calculations demonstrate that the output neutron-flux density of a pulse can be expected to reach 10¹⁷ cm^–2 s^–1 at maximum and 2 × 10¹⁴ cm^–2 s^–1 on average. The pulse duration of thermal neutrons can be 200–300 and 20–30 μs depending on the moderator and the corresponding pulse duration of the proton accelerator.

Textured Al-doped ZnO films are studied using neutron reflectometry. The films are quasiperiodic structures with a period of several nanometers. The films are inhomogeneous in a surface layer with a thickness of 10–20 nm.

The hydride phases of the intermetallic compounds GdNi₃ and DyNi₃ are synthesized at room temperature and at 273 K under a hydrogen pressure of 1–30 bar. The phase composition of the obtained samples is established using the X-ray diffraction method and the crystal-lattice parameters of the hydride phase are determined. The crystal phases are synthesized at room temperature under a hydrogen pressure of about 1 bar. At 273 K and under a pressure of 30 bar, amorphous samples are formed. The desorption of hydrogen from amorphous hydrides at 573 K leads to the formation of well-crystallized samples of the initial intermetallides. The amorphous samples are formed due to the ordering of hydrogen atoms in the metallic matrix of the hydride at low temperatures.

Re–W nanoparticles are deposited onto multiwalled carbon nanotubes by the metal organic chemical vapor deposition technique. A mixture of dirhenium decacarbonyl and tungsten hexacarbonyl is used as a precursor. Nanoparticles of hybrid materials are studied by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray phase analysis. It is found that in a wide range of ratios of the precursors (dirhenium decacarbonyl and tungsten hexacarbonyl), the crystalline component is a Re–W phase, and the morphology of the nanoparticles is the same as that of the nanodendrites.

A new, XPS-based approach to quantitative and nondestructive determination of the chemical and phase layer composition of multicomponent multilayer films is proposed. It includes a new method for subtracting the background of repeatedly inelastically scattered photoelectrons, taking into account the inhomogeneity of inelastic scattering over depth; a new way of decomposing a photoelectron line into component peaks, taking into account the physical nature of various decomposition parameters; solution of the problem of subtracting the background and decomposing the photoelectron line simultaneously; and determination of the thickness of the layers of a multilayer target using a simple equation. The phase-layer composition of nanoscale Nb and NbN films is determined, and the thicknesses of these layers are calculated.

The surface of Zr‒1%Nb zirconium-alloy samples is treated with titanium via plasma-immersion ion implantation (PIII). Afterward, TiN coatings are deposited onto the implanted and initial samples by means of vacuum-arc deposition (VAD). Before and after each of the treatments mentioned above, changes in the hydrogen sorption rate, depth distribution of elements, and surface topography are investigated. It is found that separately performed VAD and PIII reduce the hydrogen sorption rate by a factor of 2‒15. At the same time, a combination of operations so that PIII is carried out before VAD decreases the sorption rate by one‒two orders of magnitude. It is revealed that the key parameter of the aforementioned methods affecting hydrogen permeability, the depth distribution of elements, and the surface topography is the bias value applied to the sample (substrate). In the case of our setup, the optimum biases of PIII and VAD are‒1500 and‒150 V, respectively.

The results of studies into microporous scaffolds based on polycaprolactone, in particular, involving nanoparticles and microparticles of modified (silicon-containing) hydroxyapatite (hybrid scaffolds) are presented. When hydroxyapatite particles are used during the electrospinning of polymer scaffolds, their porosity is found to increase substantially and a structure with nanofibers and microfibers can be created. X-ray phase analysis demonstrates that the characteristic lines of polycaprolactone and hydroxyapatite exist in the 3D hybrid scaffold structure. According to the data of infrared (IR) spectroscopy of the hydroxyapatitepowder precursor, (SiO₄)^4– ions are embedded in its lattice. The results of studies into the surface wettability indicate that the contact angles of wetting with water are smaller for hybrid scaffolds than for pure polycaprolactone scaffolds. Adhesive and proliferative activity tests of human mesenchymal stem cells (MSCs) performed upon hybrid-scaffold cultivation on the surface, as well as histologic investigations, indicate the high biocompatibility of the samples. On the basis of a polymerase chain reaction, it is revealed that the differentiation of MSCs occurs in the osteogenic direction. On account of a porous structure, hybrid scaffolds can be employed to recover bone-tissue defects.

The structure of ceramic BiFe_1‒xZn_xO₃ multiferroic samples is investigated using the X-ray diffraction method and Mössbauer spectroscopy. X-ray diffraction analysis of the samples indicates the existence of the Bi₁₂(Bi_0.5Fe_0.5)O_19.5 impurity phase. High-temperature heating of the samples generates additional phases. The parameters of the Mössbauer spectra depend on the zinc concentration. In this case, for pure bismuth ferrite, the spectrum is a superposition between two Zeeman sextets and two paramagnetic doublets arising from two nonequivalent magnetic and electrical positions occupied by iron ions at the crystallattice sites of a sample. The replacement of iron ions with zinc ions substantially affects the spectrum parameters. This is probably related to changes in the spin-cycloid structure typical of multiferroics, the destruction of which stimulates the appearance of significant magnetoelectric interactions.

The possibility of creating a laboratory UV photolithography setup with the help of commercially available components, such as optical-mechanical positioners and UV (ultraviolet) objective lenses, is discussed. Existing technical solutions concerning the optical systems of optical lithography, which rely on object‒image reduction, are considered. The main trends in the design of such systems based on lens optics are analyzed. The theoretical and practical aspects underlying the design of similar systems are examined taking into account the basic conditions of image obtainment: congruence to the initial object, ray-path telecentricity, and achievement of the required parameters by linear fields and resolution.

For adequate description of the adsorption and self-assembly of C₆₀F₁₈ polar molecules on the surface Au(111), quantum-chemical studies of the electronic and electrical properties of a single molecule are performed. Using various procedures of density functional theory, the electric dipole moment of the molecule, distributions of the electrostatic potential, electric-field magnitude and electron density are calculated with controlled accuracy for the first time. An improved value of the electric dipole moment of the C₆₀F₁₈ molecule is obtained in a range from 10 to 11 D. The known approximation of a point dipole for electric-field strength is shown to be fulfilled within an accuracy of 30% even at distances twice greater than the size of the molecule. The structural fragments of the calculated lowest unoccupied and highest occupied molecular orbitals are assigned to their images, which were previously obtained using scanning tunneling microscopy and spectroscopy.

A method for calculating the ranges of ions with a nuclear charge of Z = 2‒10 in the region of ion velocities of 1 au < V < 20 au in carbon and methane is proposed. The dependences of the ion ranges on the charge and masses of nuclei and ion velocities in different media are analyzed. Special attention is paid to the region of intermediate ion velocities, where charge exchange processes (electron capture and loss by an ion) play an important role, as a result of which the ion charge changes during propagation through a matter.

Ferritic–martensitic steels alloyed with chromium and containing nickel impurities are considered as promising structural materials for nuclear and thermonuclear power engineering. During operation, the plastic properties of such materials degrade under the influence of neutron irradiation caused by the generation of radiation defects of the crystal structure, in particular, dislocation loops and new phases (precipitates). In this paper, an atomistic computer simulation of the interaction of mobile edge dislocations with dislocation loops having the 〈100〉 and 1/2〈111〉 Burgers vectors forming a single extended defect with Ni−Cr precipitates is performed using the classical molecular dynamics method at various temperatures (300 and 600 K). Such composite radiation-induced defects cause a change in the plastic properties of the irradiated material due to radiation hardening. The results of studying the interactions of gliding dislocations with loops (both in pure iron and in the Fe−Ni−Cr alloy, taking into account the precipitation of Ni and Cr at dislocation loops) show that the presence of an increased concentration of chromium and nickel atoms near the dislocation-loop perimeter at 300 K either decreases the critical stress for passing the dislocation through a defect (by more than 50 MPa) for the 〈100〉 loops at 300 K or increases it for the 1/2〈111〉 loops at 300 K. At a high temperature (600 K), the presence of Ni and Cr impurities near the dislocation loop leads to an increase in the critical stress for both types of loops. It is shown that the presence of an increased concentration of Ni and Cr atoms near the loop perimeter facilitates or hinders (depending on the specific dislocation-loop configuration) the transverse gliding of dislocation segments, complicates the possibility of the resplitting of junction segments of the dislocation and loop in the plane of loop location, and causes the immobilization of the loop having the [111] Burgers vector parallel to the gliding plane of the dislocation at 300 K.

The fracturing of Al−Cu alloy surface layers is studied under the action of a high-power ion beam of nanosecond duration. Local exfoliation of the surface layer whose thickness is 7‒15 μm is found to occur if the alloy is irradiated once by an ion beam with a current density of 150 A/cm². Changes in the surface composition of the irradiated alloy are detected with the help of energy dispersive X-ray microanalysis. The alloy sample surface is enriched with copper under all irradiation conditions. Possible mechanisms of the observed fractures are discussed.

Problems concerning the local ion-beam deposition of platinum from the gas phase are discussed. A mathematical model for predicting the platinum deposition rate, in which the precursor-gas characteristics and ion-beam currents are taking into account, is analyzed. A refined mathematical model describing the local ion-beam deposition of platinum, which allows for the size of the region of gallium ion-beam overlap, is proposed. The simulation results are used to reveal the dependence between the platinum-deposition rate and the size of the region of gallium ion-beam overlap. The calculation results are experimentally confirmed. The maximum platinum deposition rate is demonstrated to increase to 20 nm/s with increasing region of beam overlap. It is found that the deposition process is not converted into the etching one at a beam current of less than 80 pA despite an increase in the region of overlap and etching always dominates at a current of greater than or equal to 1000 pA.

A SiO₂/Si/CoSi₂/Si(111) heterostructure is synthesized via successive Co⁺- and O₂⁺-ion implantation into silicon followed by annealing. The optimal implantation and annealing conditions needed to obtain such a structure are determined. It is demonstrated that CoSi₂ and SiО₂ layers formed in the surface region are single- and polycrystalline, respectively.

The temperature-accelerated dynamic simulation technique based on an increase in the temperature of a system to intensify the thermally induced motion of its atoms enables the simulation of atomic systems over time periods inaccessible by means of classical molecular dynamics simulation. The technique of changing the interaction potential within the temperature-accelerated simulation proposed in this paper is aimed at compensating thermal expansion of the system when its temperature increases and to estimate the variations of the frequencies of normal modes of system vibrations. The presented examples of the simulation of two- and three-dimensional systems show that the proposed procedure of modification of the interatomic interaction potential enables one to estimate times of atomic-system transitions between states during temperature- accelerated simulation close to the data provided by classical molecular dynamics simulation. Additionally, modification of the interatomic interaction allows one to improve the accuracy of estimations of the transition probabilities at temperature-accelerated simulation, which increases the reliability of the description of nanoatomic-system evolution.