Том 12, № 3 (2018)

The review deals with studies carried out at the BM01 diffraction beam line of the European Synchrotron Radiation Facility. X-ray diffraction analysis of single-crystal proton conductors demonstrates the possibilities of a precise diffraction experiment in which phase transitions associated with the release of crystallization water and transformation of the network of hydrogen contacts are investigated. Scanning of reciprocal space with the help of a 2D detector enables us to determine the new phase symmetry in a thin-film multiferroic sample based on bismuth ferrite (the given phase is stable only under thin-film conditions). A combination of Bragg and diffusion scattering processes is employed to investigate the interdependence between the structure and dynamics of a crystal lattice and the physical properties of a relaxor material with a perovskite-like structure. The complementarity and synergy of neutron and synchrotron experiments are demonstrated using the combined study of materials from the manganese-silicide group, which has revealed a nontrivial relationship between magnetic and crystallographic chiralities in noncollinear magnets. Although the given review is limited to only a few experiments carried out by Russian scientists at the BM01 beam line, they still illustrate a variety of problems that can be solved using a modern diffraction station where the bending magnet of a third-generation synchrotron is employed as the synchrotron radiation source.

A high-resolution neutron diffractometer has been fabricated on the basis of an IN-06 pulsed neutron source at the Institute for Nuclear Research, Russian Academy of Sciences. The diffractometer incorporates two blocks of detectors with helium neutron counters and time-of-flight (TOF) focusing at scattering angles of 156°–165°. A block of new-type high-efficiency scintillation detectors of thermal neutrons based on a ZnS(Ag)/LiF scintillator and silicon photomultipliers with TOF focusing is developed and tested. Test measurements are performed, and the diffractometer resolution is estimated. The diffraction pattern of nonmagnetic NiCrAl alloy is measured and used to determine the phase composition by means of the Rietveld method. It is demonstrated that the given setup can be applied to phase analysis.

Band structure calculations have been performed on heavy rare-earths R₂Fe₁₇ compounds. The iron moments are strongly dependent on the site location and little influenced by the rare-earth partner. The Curie temperatures follow a linear trend as function of R5d band polarizations. The magneto-volume effects are well described in models where the iron moments have a rather great degree of localization. The magnetic properties of GdFe₂, at high pressures, were theoretically analysed. Both magnetic and structure transitions have been suggested, as the pressure increases.

Biomimetic materials (biocomposites) with an organic-mineral composition related to natural dental tissues (enamel and dentin) are obtained for the first time and their structural and optical characteristics are studied. It is demonstrated by a complex of structural and spectroscopic methods that in the formation of biocomposites, the introduced organic component, bearing a number of amino acids, does not affect the structure of the inorganic component (carbonate-substituted calcium hydroxyapatite) of the sample. The carbonate-substituted calcium hydroxyapatite synthesized using a biogenic source of calcium, which forms the basis of the biocomposite, has a luminescence spectrum similar to that of apatite tooth enamel. The spectrum of the intact dentin of a human tooth has a broader luminescence band than that for the enamel spectrum. It is determined that both organic and inorganic components contribute to the dentin luminescence band. The features found in the luminescence spectra of intact tissues and in simulating biocomposites can be used to develop a procedure for effective early diagnosis of the demineralization of hard dental tissues and general dental examination.

The applicability of the Monte Carlo method for modeling images obtained in a scanning electron microscope is assessed. It is shown that in the Monte Carlo method, it is impossible to take into account all the mechanisms of the interaction of electrons with matter that affect image formation. Modern random-number generators create an insufficient amount of random numbers necessary for modeling the scattering of electrons in matter. The time it takes to modeling images using contemporary personal computers is too long: it takes years of continuous computer operation. There is no evidence of correctness of the results of the Monte Carlo method when generating images. These factors prove the impossibility of using the Monte Carlo method to modeling the scattering of electrons in a solid, which is used in image formation in a scanning electron microscope.

The structure of carbon nanopillars grown without catalysis by low-temperature plasmaenhanced-chemical-vapor deposition on a silicon substrate is investigated using the suggested focused ion beam technique for preparing a sample composed of several thin plan-view foils. Studying the prepared sample by electron diffraction and bright-field transmission electron microscopy allows determination of the variation of the two-dimensionally ordered crystallite fraction along the growth direction. It us established that the crystalline phase fraction inside the nanopillars gradually decreases during the growth process. Nearly 90% of the crystalline material is located between the base and the middle of the nanopillars while their upper parts almost entirely consist of amorphous carbon.

The structural-phase state of the 50 vol % TiC/50 vol % (Ni‒Cr) surface layer of a metal-ceramic composite subjected to pulsed electron irradiation in plasma of inert gases with different atomic masses is experimentally investigated and the obtained results are presented. The regularities of the influence of the atomic mass of a plasma-forming inert gas on the characteristic features of the heterogeneous structure of the nanostructured surface layer of a metal-ceramic composite and the thickness of the surface layer with modified structure are presented and discussed. It is demonstrated that, in the case of the pulsed electron irradiation of a metal-ceramic alloy, the formation of a nanostructured surface layer significantly increases the surface-layer wear resistance and reduces the friction coefficient over the irradiated surface. An increase in the wear resistance of the surface layer and a decrease in the friction coefficient along the irradiated surface occur in accordance with an increase in the atomic mass of the plasma-forming gas under pulsed electron irradiation.

The irradiation of semiconductor structures with low-energy protons is used to control changes in their properties at a depth ranging from 0.1 to 1000 μm. Devices manufactured from such structures have high sensitivities to changes in the state of the surface region. The paper is dedicated to studying the effect of radiation-induced defects produced by low-energy protons in a heavily doped diffusion region on the properties of Si structures with an n⁺‒p junction. The structures are irradiated with a flux of protons with an energy of 40 keV and a dose of 10¹⁵ cm⁻² at a sample temperature of 83 and 300 K. The distributions of the average number of interstitial Si, vacancies, and divacancies produced by one proton under these conditions per length unit of the projective range in the diffusion layer of an n⁺‒p junction are calculated. It is shown that the number of radiation-induced defects in the distribution maximum at a depth of 0.39 μm in a layer with n-type conductivity at a sample irradiation temperature of 83 K is significantly less than that at 300 K. This conclusion is confirmed by the results of studies of electrophysical and optical properties of irradiated n⁺‒p‒p⁺ structures.

The influence of the carbamide concentration on the nitrocarburizing temperature and changes in the mass of titanium samples, which are related to the anodic dissolution and high-temperature oxidation of titanium in a vapor‒gas shell, is investigated. The modified layer structure is revealed to contain an external oxide layer (rutile) and an intermediate diffusion layer whose microhardness reaches 770 HV. It is demonstrated that an increase in the nitrocarburizing temperature stimulates growth in the oxide-layer thickness, and the diffusion-layer thickness depends on the carbamide concentration in the solution. It is found that, at 850°С, the surface roughness decreases from 1.0 to 0.3–0.5 μm and the wear rate reduces from 6.7 × 10^–7 to (1.2–1.7) × 10^–7 due to nitrocarburizing in an electrolyte incorporating 10–15 wt % ammonium chloride and 10–12.5 wt % carbamide.

By the methods of reflection-absorption IR (infrared) spectroscopy, electrical measurement and AFM microscopy, the process of the radiation-stimulated hydrogenation of the aluminum surface in the Al/ads n-hexane system under γ-irradiation at room temperate is studied. On the basis of the dose dependence of the Al surface specific resistance, two stages of the hydrogenation process in the absorbed dose range (0.5‒120 kGy) are revealed. It is established that the transition from the first to the second stage is accompanied by a decrease in the electrical conductivity of Al by 35 times and an increase in the hydride-nanolayer thickness by an order of magnitude. AFM studies of the aluminum surface relief showed that radiation-stimulated hydrogenation is accompanied by the formation of carbon-nanotube structures. A possible mechanism for the radiation-stimulated hydrogenation of aluminum is suggested.

Inelastic energy losses can be presented as two components determined by processes of the ionization of target atoms and the charge exchange of ions. These components are interrelated. The interrelation is determined by the value of the average ion charge. The energy losses during the ionization of a target atom are calculated using a parameter which characterize the effect of states of excited atoms. The difference between inelastic energy losses in gaseous and solid targets is explained.

The possible reactions between thermal F atoms and SiCF₃ surface groups are simulated using density functional theory. These reactions constitute a part of the multistage mechanism by which SiOCH films are damaged and etched by fluorine radicals. The results of simulation demonstrate that a probable channel for removing carbon-containing compounds from the surface is the generation of volatile CF₃ radicals with the simultaneous formation of SiF surface groups. The probability of the separation of a CF₄ molecule is low due to a forbidding activation barrier of ~1.4 eV.

A comparative analysis of the effect of magnetron-sputtering parameters on the formation of the structure of thin tantalum-diboride films deposited using a radio-frequency magnetron sputtering system and a sputtering system with an unbalanced direct-current magnetron is carried out. The sign and magnitude of the bias voltage is shown to significantly affect the structure of tantalum-diboride films.

A review of the most recent papers concerning the study of interatomic potentials is given. In the case of small distances, the potential values for a distance of up to 0.005a_f (a_f is the Firsov screening length) are obtained from a scattering experiment using proposed procedures. A new formula for the screening constant is put forward, and the influence of electron screening on cross sections for nuclear fusion reactions is described. In the range of medium internuclear distances, the experimental data on potentials agree well with the calculated ones obtained using the density functional approximation and the DMol software package for choosing the basis of wave functions. The first studies involving determination of the projectile—surface system potential from data on rainbow scattering during surface channeling are discussed.

The Raman spectra of kinked carbon chains with a set of end groups composed of hydrogen, silver, and copper atoms are calculated. It is analyzed how end groups, as well as the positions of impurity atoms in the chain, affect shifts characterizing the main peaks of the harmonic vibrations of chemical bonds between carbon atoms in polyyne- and cumulene-like (respectively, (–C≡C–)_n and (=C=)_n) chains.

The results obtained by the method of secondary ion mass spectrometry study of the initial stages of hydrogen interaction with the LaNi₅ alloy surface are presented. It is demonstrated that the alloy surface is partially covered with a layer of island-structure oxides. Upon impinging on clean surface regions, hydrogen forms chemical compounds with both (nickel and lanthanum) alloy components. When the amount of hydrogen increases, hydride structures with different stoichiometric compositions involving both alloy components are formed on the surface and in the near-surface region.

Structures, namely, powder and films, deposited onto vacuum-chamber walls from low-temperature vacuum arc discharge and tokamak plasma are investigated. The fractal parameters of the given structures are compared. The possible mechanisms of their formation are discussed.

The nitriding of cylindrical tubes with a length of 300 mm, an external diameter of 20 mm, and an internal diameter of 6 mm made of low-alloy structural steel 30CrN2MFA is investigated. The tubes are subjected to heat treatment (quenching at 860°C and aging at 600°C) before nitriding. Nitriding is performed at 500°C for 4 h in a N₂: H₂ = 1: 1 mixture at a total pressure of 5.3 mbar in abnormal glow discharge. The hardness after nitriding increases by 1.5‒2 times on both the external and internal surfaces of the tubes. The thickness of the hardened layer on the internal surface varies from 90 to 225 μm.

The effect of mechanical stresses of different signs on the formation of radiation defects in crystalline silicon is studied alongside the effect of strain on the accumulation of radiation defects in KEF-4.5 silicon after the implantation of protons with an energy of 140 and 500 keV and a dose of 2.5 × 10¹⁵ cm^–2. The stress-strain state of a thin circular plate with a strained surface layer is calculated. It is shown that the applied mechanical stresses generally have an effect on the thickness of the damaged layer, whose thickness decreases with an increase in compressive stresses near the surface in comparison with its thickness in the undamaged sample and grows in the opposite case.

Tubular InSbS₃ crystals are obtained for the first time by means of inadvertently growth on the surface of an antimony layer located on single-crystal indium antimonide. The crystals are studied by scanning electron microscopy, energy-dispersive analysis, and X-ray diffraction. They are established to be an independent phase. A mechanism for tubular growth is proposed.

The title of the article should read as follows:

Structural Analysis of Aluminum Oxyhydroxide Aerogel: Small Angle Scattering Studies