Vol 10, No 2 (2016)

An experiment is performed to determine the electron beam diameter using a comparison of a video signal curve from a relief structure and the one calculated based on a simplified model of curve formation. Rather than the use of an experimental curve for comparison, this model experiment suggests the use of a curve calculated from the data on electron scattering in substrate by the Monte Carlo method. The comparison results revealed the difference between the calculated diameter value and the value of diameter of a model incident beam. It appeared that the parameters of the relief structure and the electron beam affected the calculated diameter values; as a result, these values can vary by several hundred percent in some cases.

The initial stage of growth of nanoislands prepared by thermal deposition of niobium on the reconstructed surface of Si(111)-7 × 7 in ultrahigh vacuum is experimentally investigated. The morphological and electrophysical properties of niobium-based nanostructures are studied by means of low-temperature scanning tunneling microscopy and spectroscopy. It is found that upon the deposition of niobium on a substrate at room temperature, clusters and nanoislands are formed on the silicon surface, having a characteristic lateral size of 10 nm with the metallic type of tunneling conductivity at low temperatures. Upon the deposition of niobium on a heated substrate, quasi-one-dimensional (1D) and quasi-two-dimensional (2D) structures with typical lateral dimensions of up to 200 nm and three-dimensional pyramidal islands with semiconducting type of tunneling conductivity at low temperatures are formed.

We present the results of studying the effect of a weak external magnetic field on the conductivity of heterostructures containing a wide-gap polymer layer. A set of experiments is singled out for switching the metal–dielectric conductivity, controlled by a weak magnetic field. Evidence of the reliability and repeatability of key experiments are reviewed, and the effect of possible artifacts on switching of the conductivity in the heterostructures under study is discussed.

The features of the cooling of arrays of Josephson junctions fabricated from cuprate superconductors, as well as their interaction with microwave radiation during treatment in a closed-cycle cryocooler, are investigated. Estimation of microchip heating sources is carried out by measuring the current–voltage characteristics (IVCs) of the Josephson junctions. On the developed the developed experimental setup, Shapiro steps with a voltage of about 25 mV are obtained on the IVCs of the structure exposed to microwave radiation at a frequency of 75 GHz.

The evolution of electron wave packets formed from surface states in topological insulators located in an external magnetic field is studied. The electron and spin densities of the wave packets under consideration are calculated analytically and are visualized. The influence of the main characteristics of the wave packets (the spin polarization) on the splitting and the change in their forms with time is considered.

The structure of ribonucleic particles of influenza A virus of the A/California/07/09pdm strain is investigated by transmission electron microscopy and small-angle X-ray scattering. The small-angle X-ray scattering data obtained at room temperature correspond to previously reported data of ribonucleic particles of this virus. At higher temperatures, noticeable changes in the morphology of ribonucleic complexes are observed.

The impact of a nanosecond high-energy ion beam on the structure and morphology of multilayer carbon nanotubes and their ensembles is studied using transmission electron microscopy and scanning electron microscopy. It is shown that ion-beam irradiation leads to a decrease in the outer diameters of carbon nanotubes, which is related to the destruction of their outer layers. In addition, the secondary growth of carbon nanotubes with smaller diameters and the growth of bulblike formations, inside which structures with interplanar distances that are close to those of nanodiamond are fixed, are observed.

The results of studies of the morphological properties of an oxide film obtained by the anodic oxidation of a n-Si(100) single-crystal silicon wafer in distilled water in the potentiostatic mode are presented. Irrespective of the value of the applied potential and the anodic treatment time, the oxide coating is always formed as separate islands, interconnected by a thin layer of barrier oxide, the thickness of which is adjusted by the pH value of an alkaline solution (pH > 7) produced in a limited area of local oxidation.

The elemental composition of loose sediments in the Kan-i-Gut cave mine located in the foothills of the Turkestan range (Kyrgyzstan) is determined by X-ray fluorescence analysis with the use of synchrotron radiation. The samples of loose sediments are selected at different points in the cave, from the entrance to the lowest horizon. The first geochemical data on residual loose sediments in the Kan-i-Gut cave mine are obtained. They allow detailed study of the poorly studied migration of chemical elements in karstic cavities and its specific conditions, which can remain unchanged for a long time.

The crystal structure of iron-doped barium titanate BaTi_1–xFe_xO₃ is studied by neutron diffraction in the range of 0 ≤ x ≤ 0.12. At low concentrations of iron, x < 0.01, and at room temperature, these compounds have a polar structure with tetragonal symmetry with space group P4mm. The temperature of the transition of the tetragonal ferroelectric phase into the cubic paraelectric phase with space group Pm\(\bar 3\)m for an iron concentration of x = 0.01 is 390 K (for pure BaTiO₃, it is 410 K). At an iron concentration of x = 0.07, the crystal structure of the studied compounds varies, and it is described by the centrosymmetric hexagonal space group P6₃/mmc. The structural parameters of various phases of compound BaTi_1–xFe_xO₃ are determined from the experimental data.

We investigate how irradiation with high-energy ions (167-MeV ¹³²Xe²⁷⁺, 107-MeV ⁸⁴Kr¹⁷⁺, and 48-MeV ⁴⁰Ar⁸⁺) and 2.5-MeV protons affects the critical parameters of high-temperature superconductor tapes based on YBa₂Cu₃O_7–x and GdBa₂Cu₃O_7–x compounds. The ion ranges in the multilayer structures under study and the thermal regimes of the irradiated samples are calculated using SRIM and thermal-peak models. The calculated results make it possible to estimate the size of radiation-induced defects which serve as the pinning centers of Abrikosov vortices. The performed investigations enable us to reveal that, in the irradiated structures, an increase in the critical current, improvement in the adhesion between the superconducting layer and the substrate, and a reduction in internal stresses are observed under exposure to low levels of Ar- and Kr-ion irradiation. The critical current and the critical temperature decrease at higher fluences and, finally, the phenomenon of superconductivity disappears if the fluence continues to increase. In the case of 2.5-MeV proton irradiation, the radiation resistance of the GdBa₂Cu₃O_7–x samples is found to be higher than that of the YBa₂Cu₃O_7–x tapes.

The interaction of interstitial hydrogen (H) with dislocations and point defects in tungsten (W) is studied via numerical simulation within the framework of classical molecular dynamics (MD). Two alternative models are considered to describe the interatomic interactions: the embedded-atom method (EAM) and the bond-saturation model (the bond-order potential (BOP)). The calculated results are compared with data obtained via ab initio quantum-mechanical simulation. The potential developed recently within the framework of the EAM model demonstrated better agreement with the ab initio results than the BOP one. Molecular- statics calculations showed that hydrogen atoms are attracted by the dislocation core in both cases of screw and edge dislocations. The classical MD simulation of hydrogen diffusion in the vicinity of the edge dislocation demonstrated one-dimensional migration along the dislocation line.

The results of experimental and computer-based studies of the sputtering and erosion of carbonmaterial surfaces under high-fluence irradiation with 30-keV Ar⁺ ions at various angles of ion incidence are given. The irradiation of highly oriented pyrolytic graphite (HOPG) and polyacrylonitrile fibers of carbon–carbon composites, which are characterized by surface corrugation, is considered. A model is proposed for taking into account the influence of parameters of symmetric corrugation on the characteristics of sputtering of the irradiated materials. Calculation shows that taking experimental values of the corrugation slopes into account allows one to explain the angular dependence of the sputtering yield of HOPG. It is found that the pronounced (about two times) suppression of sputtering within the range of incidence angles of 60°–80° is connected with the rear (relative to the ion beam) faces of the corrugation being obscured. Unlike the case of the normal incidence of ions, the sputtering yield at large incidence angles decreases as the corrugation period increases due to blocking of the sputtering of the rear and neighboring faces of microrelief elements.

The effect of a nanosecond high-power ion beam on thin polymer layers of chlorinated polyvinyl chloride and polymethyl methacrylate containing ferrocene as an additive is investigated. Arrays of carbon nanofibers with a characteristic diameter of 30–160 nm and lengths of up to 15 m are formed on the surface of the chlorinated polyvinyl chloride. The same effect on polymethyl-methacrylate layers leads to intense cavitation of the surface layer. The possible mechanisms of the formation of carbon nanofibers in chlorinated polyvinyl chloride with ferrocene additive under the action of a high power ion beam are discussed.

A series of experiments is carried out to study the passage of electrons with an energy of 10 keV through glass macrocapillaries of tapered shape with an input—output diameter ratio of 1 : 10 and 1 : 5. Experiments are performed for different tilt angles of the capillaries with respect to the incident-beam axis. The results demonstrate a significant increase in the current density of a beam passed through the capillaries.

The formation of a topological structure in thin films of the high-temperature superconductor YBa₂Cu_3O7–δ (YBCO) using ion implantation is studied. The crystal structure and electrical properties of the initial film and the formed insulating regions are investigated. The critical temperature and critical current are measured for microbridges with a width of 3–50 μm fabricated by ion implantation. The results indicate the effectiveness of the ion-implantation method for manufacturing topological structures in YBCO films.

The results of estimating different projection approximation schemes (a modified least-squares method and the Galerkin and Ritz methods) are presented. They are used to simulate the distribution of minority charge carriers, which is observed as a result of the diffusion of minority charge carriers generated by a broad electron beam in a homogeneous semiconductor material. Certain computational features of the implementation of the considered methods are considered.

In this paper the results of the investigation of Si-Cr_x resistive cermet films, which are promising for the development of broadband microbolometers of the microwave range, are presented. A model of the conductivity of cermet films based on the theory of transport in granular metals and diluted semiconductors is proposed.

The angular distributions of reflected medium-energy ions are numerically calculated for the case of oblique incidence on the target surface. Calculations are performed by solving the one-velocity transport equation involving the scattering cross section of a truncated Coulomb potential. The results obtained via the method of discrete streams are a generalization of well-known Chandrasekhar data corresponding to simpler scattering cross sections. Theoretical angular distributions are compared with those obtained experimentally.