Volume 11, Nº 2 (2017)

The composition and structure of carbon nanowalls formed on silicon substrates from the gas phase of hydrogen and methane activated by a direct-current glow discharge are studied by methods of scanning electron microscopy, X-ray diffractometry, IR spectroscopy, and Raman spectroscopy. It is shown that nanowalls are comprised of a porous material consisting of curved lamellar (flaky) crystallites with a thickness of 3–10 nm. The effect of heat treatment and laser irradiation in air on the structure of the carbon nanowalls is studied, and the current–voltage characteristics of field-emission cathodes on their basis are obtained. The heating temperatures and laser-radiation power densities at which the morphology of the surface of carbon nanowalls changes and the characteristics of field-emission cathodes on their basis are determined.

Samples of composites, in which ethylene-tetrafluoroethylene copolymer is used as a matrix and quasicrystalline Al−Cu−Fe powder as a filler with 0, 1, 2, 4 and 8 vol % concentrations, are prepared. Electron microscopy studies of the sample structure are carried out. The influence of the filler on the crystallinity and temperatures of sample melting and destruction is investigated. The mechanical and tribological properties of the samples are tested. It is found that an increase in the filler content changes neither the mechanical nor thermodynamic characteristics of the material but significantly improves the tribological characteristics. The friction coefficient decreases twice at 1 vol % of the filler and the wear resistance increases by 40 times at 8 vol %. Experimental data indicate the probability of good adhesion of the filler particles to the fluoropolymer matrix. The composites under investigation may be of interest as promising materials for polymer friction bearings.

Active layers of electrocatalysts are prepared by the ion-beam assisted deposition (IBAD) of platinum onto carbon-based AVCarb® Carbon Fiber Paper P50 and Toray Carbon Fiber Paper TGP-H-060 T supports and Nafion® N 115 polymer membrane electrolyte in the mode where the deposited metal ions are used as ions assisting the deposition process. Metal deposition and mixing of the deposited layer with the substrate under an accelerating voltage of 10 kV by the same metal ions are carried out from a neutral fraction of metal vapor and the ionized plasma of a pulsed vacuum-arc discharge, respectively. The composition and microstructure of the surface layers obtained are studied by Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM), electron-probe microanalysis (EPMA), and X-ray fluorescence (XRF) analysis. The platinum concentration in the layers is (0.5–1.5) × 10¹⁶ at/cm². The prepared electrocatalysts exhibit activity in the process of the electrochemical oxidation of methanol and ethanol, which form the basis for the principle of operation of low temperature fuel cells (direct methanol fuel cells (DMFC) and direct ethanol fuel cells (DEFC)).

Based on X-ray diffraction and electron microscopy data on morphological inhomogeneities at the interfaces in Fe−B ribbons, the boundary boron concentration separating the crystal and amorphous states upon spinning (~10 at %) is established. A modulated isotropic stochastic wave structure is detected, the relaxation of which can be presented as spinodal decomposition.

It is proposed that the dimension of similarity of the relief profile be used as an integral characteristic of solid-surface roughness. This parameter coincides with the fractal dimension of the line only in the case of the same length scales in the surface plane and in the direction that is normal to it. The interrelation between the dimension of similarity and the usually used fractal dimension of the relief profile is obtained and analyzed. The optical surface of single-crystal Ge is used as an example in order to reveal the correlation between the dimension of similarity of the relief surface and the transmission coefficient in the infrared range.

GaAs lattice “superdilation” caused by an introduced tellurium impurity, which is well known in publications, is experimentally studied. This phenomenon consists in the fact that the GaAs-lattice dilation can be more than 10 times greater than expansion that would appear upon the replacement of arsenic atoms with tellurium atoms if calculations are performed using the current-carrier concentration and Vegard’s law. The given phenomenon has already been observed at n_Te > 3 × 10¹⁸ cm^–3. A series of GaAs epitaxial layers heavily doped with tellurium and grown via metal-organic chemical vapor deposition are investigated using high-resolution X-ray diffractometry (HRXRD), secondary-ion mass spectrometry (SIMS), and the Hall effect. It is demonstrated that, despite a high Te concentration (10²⁰‒10²¹ cm^–3) in the layer and variations in the growth conditions, the concentration estimates based on HRXRD data depend linearly on the results of elemental analysis performed by means of SIMS. The GaAs lattice expands even somewhat slighter as compared to the case where arsenic atoms are replaced with all Te atoms injected into the layer. At the same time, the Hall carrier concentration decreases sharply beginning at 2 × 10²⁰ cm^–3. In accordance with the obtained results, the examined phenomenon can be interpreted as the strong compensation of donor and acceptor carriers rather than as superdilation.

A method for determining the depth distribution of ion-implanted impurity atoms in semiconductors is developed. The method consists in measuring the concentration of impurities by X-ray fluorescence analysis upon the ellipsometry controlled removal of thin semiconductor layers. It is found that the prolonged low-energy X-ray radiation exposure of an ion-implanted semiconductor layer leads to a change in the distribution profile of the ion-implanted impurity atoms.

The channeling of atomic and molecular particles in carbon nanotubes is considered in the presence of vacancies on the walls and of adsorbed atoms inside them. It is shown that the significant influence of the indicated disturbance of nanotube structures greatly affects channeling, which makes it possible to use beams of atomic and molecular particles to probe nanotubes.

The photo-induced direct current in a system consisting of a one-dimensional Rashba ring with conductors connected to it is calculated. The current is produced under the action of circularly polarized radiation incident on the ring in the presence of Rashba spin—orbit coupling. The charge and spin currents in conductors are expressed in terms of the coefficients of the electron transmission through the ring with inelastic interaction with radiation taken into account. It is shown that the spin current is a complex function of the magnetic flux through the ring, of the radiation frequency, and the spin—orbit coupling constant.

A new class of experimental techniques is presented which allows the behavior of elementary collective excitations (quasiparticles) in solids to be studied at the mesoscopic scale. New experimental equipment is being constructed in the classical scheme of an atomic force microscope in which the sensor of primary information is a cantilever. The defining feature of the proposed sensor based on a cantilever is the addition of a generator and detector of quasiparticles to its design. The generator is located either on the tip of the cantilever or in close proximity to the needle on the cantilever, so that the flow of quasiparticles emitted by the generator propagates along the needle of the cantilever to the point where the needle tip touches the surface. The detector is located in a similar way. The measured quantity is the reflection coefficient of the flux of quasiparticles from the interface between the cantilever needle tip and the surface being scanned.

To reveal the effect of isomorphic substitution on the kinetics of phase transitions, single crystals of (K_1–x(NH₄)_x)mH_n(SO₄)_{(m + n)/2} · yH₂O solid solutions are grown from the K₃H(SO₄)₂–(NH₄)₃H(SO₄)₂–H₂O system. The chemical composition of the single crystals grown is determined by energy dispersive X-ray microanalysis. The thermal, optical and dielectric properties of (K_1–x(NH₄)_x)_mH_n(SO₄)_{(m + n)/2} · yH₂O single crystals are studied. The structural conditionality of the physical properties of these compounds is determined on the basis of the data of precision studies of the structure.

The reasons underlying the selective acceleration of the etching of heavy-ion tracks in polyethylene terephthalate irradiated by ultraviolet radiation (UV) are examined. The use of high-performance liquid chromatography, atomic-force microscopy, and infrared (IR) spectroscopy enable us to ascertain that etching is accelerated mainly due to the photodestruction of radiolysis products, which leads to the formation of an additional amount of low-molecular products with carboxyl groups in the region of tracks, thereby ultimately accelerating the polymer-etching process.

Structural changes in MK-40 sulfocation-exchange membrane material are estimated after the electrodialysis of natural waters. The reasons for a deterioration of its operational properties under the influence of various factors are revealed. Differences in the surface and bulk microstructures of membrane samples, which arise after long-term operation in electrodialysis apparatuses of various types, are visualized via scanning electron microscopy. The membrane extracted from an electrodialyzer-desalinator is characterized by an increase in macroporosity. The membrane from the near-electrode section of a reverse electrodialysis unit is distinguished by the fact that slightly soluble compounds are formed both on the membrane surface and in its bulk (salt contamination). It is established that morphological changes and sedimentation caused by the electrodialysis of natural waters affect the electrochemical and physical-chemical properties of the MK-40 sulfocation-exchange membrane. The growth in membrane macroporosity in the case of the longterm desalination of natural waters is the primary reason for an increase both in the electroconductivity against the background of losses in the exchange capacity and selectivity and in the water content and diffusion permeability. It is ascertained that the membrane transport properties deteriorate due to sedimentation which affects not only the membrane surface but also its bulk.

A conceptual model of an X-ray source based on a field emission cathode and a transmission-type target combined with a silicon X-ray window is suggested. By numerical simulation, it is shown that the proposed structure can generate a substantial emission current. It is possible to obtain a small focal spot at the target and, therefore, a high resolution. The parameters of targets providing the maximum X-ray emission intensity are determined. It is shown that effective generation is reached in a 0.25-μm-thick tungsten film and a 0.13-μm-thick molybdenum film. The transparency of a 1–2-μm-thick silicon membrane to X-rays and sufficient mechanical strength of the membrane against a pressure drop on the order of 2 atm are demonstrated, which indicates the possibility of its application as an X-ray window.

The results of investigating the plasma-immersion ion implantation of titanium into Zr–1Nb alloy from arc-discharge plasma are presented. The investigations are performed using 1.5-kV bias voltage applied to the sample by means of a coaxial plasma filter for 5, 15, and 30 min. Scanning electron and atomic-force microscopy data demonstrate that, after implantation, grains with sizes of ~50–100 nm and craters with lateral sizes varying from ~1 μm to vanishingly small values are detected on the surface. Energy-dispersive X-ray spectroscopy data indicate the formation of an oxide film under titanium implantation. It follows from X-ray diffraction analysis that implanted titanium is in the dissolved state and the crystal-lattice-parameter ratio c/a increases after ion implantation. The layer-by-layer elemental analysis of the implanted layer performed via optical emission spectroscopy is evidence that the titanium-concentration maximum is shifted to larger depths with incresing implantation duration.

The features of phase-formation mechanisms (PFMs) inherent to various temperature stages of surface phase creation are discussed with the locality of thermostimulated surface heterosegregation processes taken into account. The contributions of diffusion and sublimation processes to PFMs are estimated. It is demonstrated that pressure (vacuum) affects diffusion, adsorption, sublimation, and chemical reactions during thermostimulated segregation. The segregant type and inclination to segregation are predicted for compounds with a substantial difference between the partial pressures of the vapors of constituent components. The general PFM on the composite-oxide surface as a result of segregation is proposed.

The results of studying the effect of thermal and laser annealing on the distribution profiles of phosphorus and boron atoms in Si(111), implanted with different energies and radiation doses, are presented. It is demonstrated that an almost uniform distribution of impurity atoms can be obtained in the near-surface region of Si(111) by means of high-dose ion implantation and thermal and laser annealing. By the phased ion implantation of P⁺ and B⁺ into different sides of Si(111) with a gradual decrease in energy and radiation dose, p–i–n structures with a controlled thickness of the p and n regions are obtained, which is of great practical importance in the establishment of various device structures.