Vol 10, No 5 (2016)

A semiempirical model describing how images are formed in a scanning electron microscope operating in the backscattered electron collection mode is discussed. The model involves four imaging mechanisms. The model and the experiment are compared for grooves in silicon with rectangular and trapezoidal relief profiles.

The results of analysis of the oscillation intensity of RHEED specular reflection during the MBE growth of CaF₂/Si(111) structures in a wide temperature range from 100 to 600°С are presented. It is shown that the preliminary formation of a 2D Si buffer layer provides the two-dimensional growth of CaF₂ layers. Possible reasons which for the disruption of 2D growth at high substrate temperatures are discussed.

The surface of frost-resistant elastomers (rubbers) based on nitrile-butadiene rubber and propylene- oxide rubber (pure and modified with fillers: ultrafine PTFE and carbon black) is investigated. Tribological tests show that the addition of carbon black produced the greatest effect: the friction coefficient decreases to 0.2 and remains virtually constant during cooling. Surface and subsurface defects are detected by SEM. These defects can affect the processes in the zone of friction and destruction of the sliding surface of rubber. It is demonstrated that the modification of propylene-oxide rubber results in surface smoothing; the effect is the most pronounced in the samples modified with carbon black. The potential to use scanning probe microscopy for local investigation of the surface of rubber is assessed. A conclusion is made about the adhesive properties of surfaces based on the obtained force–distance curves. The investigation of vibration parameters of a probe in contact with the surface provides an opportunity to estimate the surface elasticity. It is shown that the addition of carbon black results in an increase in hardness of the rubber samples and a drastic reduction in adhesion. At the same time, the introduction of ultrafine PTFE leads to a slight enhancement of the adhesion and hardness. It is concluded that carbon black is the best modifying additive for the studied elastomers.

Structures, each of which is composed of a conducting substrate with a protective dielectric layer containing an array of equal-sized pores formed under the action of high-energy ions and chemical etching, are created. The created pores are electrochemically filled with nickel nanoparticles. With atomic-force microscopy (AFM), it is established that Ni nanoparticles are generated exclusively within ion tracks without film formation on the surface of a silicon-dioxide layer. Histograms illustrating the nanoparticle-diameter distribution are constructed, and areas of the nickel nanoparticles are calculated. The electrochemical and electrocatalytic properties of Ni nanoparticles inherent to ethanol-oxidation reactions are investigated. The catalytic activity per unit area of the nanocatalyst is estimated using voltammograms, AFM data, and histograms characterizing the particle size distribution.

The effect of irradiation on the dislocation structure of epitaxial GaN films, grown by the lateral-overgrowth method, is studied using the electron-beam-induced current mode in a scanning electron microscope. Low-energy electron-beam irradiation is found to lead to the gliding basal-plane dislocations even at very low excitation levels. Changes in the relative contrast of two segments of adjacent basal-plane dislocations may also indicate dislocation movement in the prismatic planes.

The possibilities of changing the conductivity of surface films during electrolysis are studied. The results of experimental research into films on nickel contacts are presented. From a comparison of ellipsometric, X-ray diffraction, and Auger-spectrum measurements of nickel coating surfaces obtained from electrolytes with organic components, it is revealed that the structure and composition of the surface films undergo changes which result in a decrease in the contact resistance. This makes it possible to employ such films in low-current contacts instead of silver or silver-alloy coatings.

Layers formed by the ion-beam-assisted deposition of cadmium, zinc, and aluminum onto the surface of carbon and stainless steels to protect aluminum and its alloys from corrosion in the case of their contact with steel parts are investigated. The protective layers are created via ion-beam-assisted deposition, in which metal deposition and mixing of the deposited layer with the substrate surface (this process is implemented by accelerated (U = 5 kV) ions of the same metal) occurs, respectively, from a neutral vapor fraction and the vacuum arc plasma of a pulsed electric-arc ion source. The morphology and composition of the generated surface layers are studied by means of scanning electron microscopy, electron-probe microanalysis, and Rutherford backscattering spectrometry. The layer composition is revealed to include atoms of the deposited metal, the substrate material, oxygen, and carbon. The layer thickness varies from ~50 to 80 nm, and the deposited metal content of the layers is ~(1.0–3.5) × 10¹⁷ atom/cm². Corrosion tests of the aluminum and its alloy in contact with the materials under study confirm the efficiency of the ion-beam modification of steel surfaces.

The characteristics of a spin-wave neutron interferometer comprising two parallel magnetic mirrors located in noncollinear to the magnetizations of the mirrors are investigated. The device can be used to study the properties of the neutron wave packet and measure the time and spatial correlations of material densities in the medium and on the surface. The interferometer’s sensitivity and the observed neutron coherence length are estimated using experimental data. The possible applications of neutron spin-echo spectrometry based on the two-mirror interferometer are discussed.

The possibility of focusing an X-ray beam from a laboratory radiation source using a short-focus refractive composite lens is shown. The lens consists of 161 spherical biconcave epoxy lenses, each with a curvature radius of 50 μm. A Metal Jet (Excillium^TM) microfocus X-ray tube, with a focal-spot size of 20 μm and containing a liquid helium anode, is used as a radiation source. The size of the focal spot in the image plane is 2.4 μm, which corresponds to the theoretical estimate. The possibility of using the composite refractive lens to form a parallel polychromatic X-ray beam is demonstrated. The results obtained allow discussion of the possibility of applying short-focus refractive X-ray lenses for X-ray microanalysis using laboratory sources; such microanalysis is currently a prerogative of synchrotron radiation sources only.

The effect of convective flows caused by the changing direction of the residual gravitational vector relative to the solidification front on the radial inhomogeneity (macrosegregation) of the dopant distribution in semiconductor crystals is studied within the context of mathematical and physical simulation for terrestrial and space conditions. Theoretical calculations and experimental research are carried out by the example of the growth of Ge crystals and their heavy doping with Ga (10¹⁹ сm^–3). The velocities of convective flows near the solidification front which lead to radial macroinhomogeneity in the grown crystals are theoretically calculated. The requirements to obtain homogeneous semiconductor crystals under real microgravity conditions are formulated.

Experiments are carried out for the self-propagating high-temperature synthesis of TiC–NiCr cermets, implemented in a mechanically activated powder mixture of Ti–C–NiCr in the free combustion mode and under pressure. It is found that an increase in the volume fraction of the binder decreases the size of TiC inclusions in particles obtained by the mechanical grinding of synthesized cermet compacts. A CCDS2000 computerized facility developed at the Lavrentyev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, is used to sputter the coatings. The results of comparison of the characteristics of detonation coatings made from the powders produced in this work and commercial Cr₃C₂–NiCr powder are given. The prospects of employing the self-propagating high-temperature synthesis of TiC–NiCr powders for the thermal spraying of wear resistant coatings are discussed.

Correction coefficients to the photoemission intensity taking into account the processes of multiple elastic scattering in finite-thickness layers are introduced. The presented procedure is based on a description of X-ray photoelectron spectroscopy signals using solutions to boundary-value problems for the equations of photoelectron transport by means of invariant-embedding methods. Exact numerical and smallangle solutions to the obtained equations are presented. A generalization to the case of description of the photoemission cross section is obtained taking nondipole corrections into account.

Multicomponent nanocrystalline coatings synthesized by the plasma-assisted vacuum arc method at high-temperatures are studied in situ by the X-ray diffraction method using synchrotron radiation. The main features of these coatings are superhardness (39–45 GPa) and nanocrystalline structure (5–20 nm). Analysis of the results of structural and phase investigations and the physical and mechanical characteristics after high-temperature treatment in air is presented.

The results of investigating the optical properties, chemical composition, and crystal structure of tungsten-oxide films annealed in vacuum and air at 700°C are presented. The films are deposited by means of reactive dc magnetron sputtering. The samples involving single films, as well as heterostructures with tungsten- and titanium-oxide films, located on quartz glass substrates are examined. It is ascertained that, in different samples, annealing leads to different changes in the optical properties, chemical composition, and crystal structure of the films.

The results of studying the phase and elemental compositions, imperfect substructure, and mechanical and tribological properties of commercially pure VT1-0 titanium subjected to combined treatment, which involves nitriding in low-pressure gas-discharge plasma and nitride coating deposition, are presented. The regularities are analyzed, the physical mechanisms of structural modification are discussed, and the optimal impact modes allowing a multiple increase in the microhardness and wear resistance of the material are revealed.

By methods of optical, scanning and transmission electron diffraction microscopy and microhardness and tribology parameters measurement the changes regularities of structure-phase states, defect substructure of rails surface after the long term operation (passed tonnage of gross weight 500 and 1000 mln. tons) were established. It is shown that the wear rate increases in 3 and 3.4 times after passed tonnage of gross weight 500 and 1000 mln. tons, accordingly, and the friction coefficient decreases in 1.4 and 1.1 times. The cementite plates are destroying absolutely and cementite particles of around form with the sizes 10–50 nm are forming after passed tonnage 500 mln tons. The appearance of dynamical recrystallization initial stages is marked after the passed tonnage 1000 mln tons. The possible mechanisms of established regularities are discussed. It is noted that two competitive processes can take place during rails long term operation: 1. Process of cutting of cementite particles followed by their carrying out into the volume of ferrite grains or plates (in the structure of pearlite). 2. Process of cutting, the subsequent dissolution of cementite particles, transition of carbon atoms to dislocations (into Cottrell atmospheres), transition of carbon atoms by dislocations into volume of ferrite grains or plates followed by repeat formation of nanosize cementite particles.

By methods of modern physical materials science the investigations analysis of phase composition, defect substructure, mechanical and tribological properties of Cr–Nb–C–V containing coatings formed in surfacing on martensitic wear resistant steel Hardox 450 were carried out. It was shown that surfacing resulted in the formation of high strength surface layer 6 mm in thinness. This layer had wear resistance 138 times greater than that of the base and friction coefficient 2.5 times less. On the basis of the investigations by methods of X-ray structural analysis and transmission diffraction electron microscopy it was shown that increase strength and tribological properties of surfacing metal were caused by its phase composition and state of defect substructure, namely, availability of interstitial phases (more than 36%) and martensitic type of α-phase structure.