Crystallography Reports最新文献

The surface topography and density of unoccupied electronic states at thermal deposition of ultrathin dibromo-bianthracene films on the ZnO surface have been studied. The electronic characteristics of unoccupied electronic states during growth of dibromo-bianthracene films to a thickness of 10 nm have been investigated by total current spectroscopy using a probe electron beam. The experimental dependences have been analyzed using theoretical calculation of the orbital energies for dibromo-bianthracene molecules by the method of density functional theory (DFT).

Titanium and zirconium alloys are indispensable structural materials in many technical applications due to their unique mechanical and physicochemical properties. Titanium and zirconium belong to the fourth (“titanium”) group, due to which one would expect them to exhibit a similar character of hydrogen permeability through alloys of these metals. The results of experiments on the hydrogen permeability of these alloys are compared and analyzed. It is revealed that the hydrogen permeation kinetics for both alloys is mainly determined by the low rate of surface processes and phase transformations, occurring as a result of increasing hydrogen concentration. It is shown that the hydrogen permeability method can be used to find the terminal solid solubility of hydrogen in metals.

Systems with a focused ion beam, using gas field ion sources, are described. The principles of operation and ways of formation of these sources, in which the effective ionization region is determined by sizes of a single atom, are considered in the historical context. The described systems have a wide range of applications, both in the field of scanning ion microscopy in combination with various analytical methods and in the field of high-resolution modification of electrical, optical, magnetic, and other properties of materials. This modification, based on ion-induced changes in the structure of material, is most pronounced in crystalline semiconductors, superconductors, and magnets.

The possibilities of the luminescence method for studying Si–oxide and Si–SiO₂–oxide structures have been demonstrated. A model of the electronic structure of Ta₂O₅ and TiO₂ layers is proposed, which explains the shape of the spectral luminescence distribution independent of the excitation way. A comparison of the luminescence spectra of single oxide layers with the spectrum of Si–SiO₂–oxide structures made it possible to draw conclusions about the interaction between layers during layered structure formation and estimate the band gap: 4.4 and 3.3 eV for Ta₂O₅ and TiO₂, respectively. The formation of Ta₂O₅ on the SiO₂ surface led to transformation in the SiO₂ surface region, manifesting itself in weakening of the luminescence band at 1.9 eV and formation of defects (luminescence centers) in the vicinity of 3 eV. Synthesis of TiO₂ on the surface of SiO₂ was not accompanied by any changes in the luminescence spectra.

Aluminum nitride films have been synthesized by reactive magnetron sputtering on n-Si(100) substrates. AlN layers with thicknesses from 2 to 150 nm were obtained to establish a correlation between the structure of the films and their electrical conductivity. Electron microscopy revealed that the amorphous structure of the films passes to nanocrystalline one while moving away from the substrate surface. Films with thicknesses below 20 nm had a high conductivity: up to 10 (Ω cm)^–1; with an increase in thickness the conductivity dropped to 10^–7 (Ω cm)^–1. The high conductivity of thin AlN layers is believed to be due to the high density of the boundaries of grains built-in into amorphous matrix.

The synthesis of submicron particles in the nonequilibrium processes occurring in a capillary electrode–aqueous electrolyte system on noble metal (gold, silver, or platinum) electrodes under the action of microsecond current pulses is reported. The variations in the value and sign of a voltage pulse on the “sacrificial” electrode affect the shape and composition of nanoparticles. Nanostructures of characteristic crystallographic shapes are obtained.

This work is a continuation of the previous study of the synthesis of intermetallic hydride compound Mg₂NiH₄ in the reaction between a nickel foil and magnesium hydride MgH₂ in a hydrogen atmosphere at pressures exceeding the decomposition pressures of both MgH₂ and Mg₂NiH₄. The synthesis was performed at temperatures of 400 and 475°С. With allowance for the results obtained previously at a temperature 450°С, it was found that, after some incubation time, the thickness of grown Mg₂NiH₄ film depends linearly on time. During incubation, a sublayer of intermetallic compound MgNi₂ is synthesized. The set of these data validates the previously proposed synthesis mechanism, where the limiting factor is the diffusion entry of nickel atoms with a constant rate over the MgNi₂ sublayer. Based on the analysis of X-ray diffraction (XRD) data, it was concluded that the MgNi₂ sublayer thickness is approximately the same for all three synthesis temperatures. The film growth rates were found for all three temperatures using thermal desorption spectroscopy, and the kinetic parameters of the diffusion of nickel atoms in the sublayer of intermetallic compound MgNi₂ were determined based on these data.

The most important structure types of nonmetals belonging to the VIII–IV groups and their importance for the development of the ideas about the composition and structure of the deep shells of the Earth and terrestrial-group planets are analyzed. The structural features of gas hydrates and their possible role in geological processes are considered. The structures of inert gases, hydrogen, and astrophysical ices in the Earth and other planets of the Solar system are presented in the light of new data. The modern concepts of the crystal chemistry of carbon polymorphs, genetic types of diamond, the indicator role of inclusions in its crystals, and conditions of its formation in nature and in model experiments are reviewed.

The minerals belonging to the class of carbonates constitute 18% of the Earth’s sedimentary shell, which is 1.7 wt % of the Earth’s crust mass. Carbonates are the main minerals of marine sediments. This is a widespread but crystallochemically understudied class of minerals, which includes 290 species. Among the 90 anhydrous carbonates, two large groups are distinguished, which include minerals with rhombohedral and orthorhombic symmetries, accumulating 90% of carbon of the Earth’s crust. The characteristic structural features of the main representatives of these groups and other common carbonates are considered. Data on possible transformations of carbonates in deep geospheres are reported.

The main structure types of the large group of oxide and hydroxide minerals are characterized. A particular attention is paid to the new data on the structural transformations of high-pressure minerals (which are of geophysical interest) occurring in the deep interior of Earth. These minerals include (Fe,Ni) oxides with ilmenite and post-spinel phase structures, silica polymorphs, etc. The crystal structures of basic minerals of the upper mantle, transition zone, and lower mantle, as well as the minerals of iron–manganese concretions, are characterized. The structural principles of the oxides used in ion batteries as cathode materials are considered.