Том 61, № 6 (2016)
- Год: 2016
- Статей: 21
- URL: https://journals.rcsi.science/1063-7745/issue/view/11935
Reviews
Electron microscopy methods in studies of cultural heritage sites
Аннотация
The history of the development and application of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray microanalysis (EDXMA) in studies of cultural heritage sites is considered. In fact, investigations based on these methods began when electron microscopes became a commercial product. Currently, these methods, being developed and improved, help solve many historical enigmas. To date, electron microscopy combined with microanalysis makes it possible to investigate any object, from parchment and wooden articles to pigments, tools, and objects of art. Studies by these methods have revealed that some articles were made by ancient masters using ancient “nanotechnologies”; hence, their comprehensive analysis calls for the latest achievements in the corresponding instrumental methods and sample preparation techniques.
Optical and luminescent VUV spectroscopy using synchrotron radiation
Аннотация
The main processes of energy relaxation occurring in solids upon high-energy excitation are described, and the information that can be obtained by vacuum ultraviolet (VUV) spectroscopy for each relaxation stage is presented. The theoretical and experimental results obtained by the authors using synchrotron radiation are reported.
Nanocrystalline sp2 and sp3 carbons: CVD synthesis and applications
Аннотация
The design and production of innovative materials based on nanocrystalline sp2- and sp3-coordinated carbons is presently a focus of the scientific community. We present a review of the nanostructures obtained in our labs using a series of synthetic routes, which make use of chemical vapor deposition (CVD) techniques for the selective production of non-planar graphitic nanostructures, nanocrystalline diamonds, and hybrid two-phase nanostructures.
Diffraction and Scattering of Ionizing Radiations
Time and space domain separation of pulsed X-ray beams diffracted from vibrating crystals
Аннотация
It is known that a set of additional reflections (satellites) may arise on rocking curves in the case of X-ray diffraction in the Bragg geometry from crystals where high-frequency ultrasonic vibrations are excited. It is shown that, under certain conditions, the pulse wave fields of the satellites and main reflection may be intersected in space (playing the role of pump and probe beams) and in time (forming interference superlattices).
Study of a macrodefect in a silicon carbid single crystal by means of X-ray phase contrast
Аннотация
The morphology of a macrodefect in a single-crystal silicon carbide wafer has been investigated by the computer simulation of an experimental X-ray phase-contrast image. A micropipe, i.e., a long cavity with a small (elliptical in the general case) cross section, in a single crystal has been considered as a macrodefect. A far-field image of micropipe has been measured with the aid of synchrotron radiation without a monochromator. The parameters of micropipe elliptical cross section are determined based on one projection in two directions: parallel and perpendicular to the X-ray beam propagation direction, when scanning along the pipe axis. The results demonstrate the efficiency of the phase contrast method supplemented with computer simulation for studying such macrodefects when the defect position in the sample volume is unknown beforehand.
Structure of Inorganic Compounds
New crystals of the CsHSO4–CsH2PO4–H2O system
Аннотация
Cs6H(HSO4)3(H2PO4)4 crystals, grown for the first time based on an analysis of the phase diagram of the CsHSO4–CsH2PO4–H2O ternary system, have been investigated by structural analysis using synchrotron radiation. The atomic structure of the crystals is determined and its specific features are analyzed.
Defect structure of TiS3 single crystals of the A-ZrSe3 type
Аннотация
The defect structure of TiS3 single crystals of the A-ZrSe3 type has been determined based on X-ray diffraction data. Shear defects manifest themselves as displacements of ab layers (which can imitate a twin) by ∼0.5a. Regular shears facilitate the formation of a superstructure along the c axis. A model of defect in the layer structure is proposed to explain the atomic displacements at an angle to the layer plane.
Pyroxenoids of pyroxmangite–pyroxferroite series from xenoliths of Bellerberg paleovolcano (Eifel, Germany): Chemical variations and specific features of cation distribution
Аннотация
The pyroxferroite and pyroxmangite from xenoliths of aluminous gneisses in the alkaline basalts of Bellerberg paleovulcano (Eifel, Germany) have been studied by electron-probe and X-ray diffraction methods and IR spectroscopy. The parameters of the triclinic unit cells are found to be a = 6.662(1) Å, b = 7.525(1) Å, c = 15.895(2) Å, α = 91.548(3)°, β = 96.258(3)°, and γ = 94.498(3)° for pyroxferroite and a = 6.661(3) Å, b = 7.513(3) Å, c = 15.877(7) Å, α = 91.870(7)°, β = 96.369(7)°, and γ = 94.724(7)° for pyroxmangite; sp. gr. \(P\overline 1 \). The crystallochemical formulas (Z = 2) are, respectively, M(1–2)(Mn0.5Ca0.4Na0.1)2M(3–6)(Fe, Mn)4M7[Mg0.6(Fe, Mn)0.4][Si7O21] and M(1–3)(Mn, Fe)3M(4–6)[(Fe, Mn)0.7Mg0.3]3M7[Mg0.5(Fe, Mn)0.5][Si7O21]. For these and previously studied representatives of the pyroxmangite structural type, an analysis of the cation distribution over sites indicates wide isomorphism of Mn2+, Fe2+, and Mg in all cation M(1–7) sites and the preferred incorporation of Сa and Na into large seven-vertex M1O7 and M2O7 polyhedra and Mg into the smallest five-vertex M7O5 polyhedron.
Crystal structure of a new polar borate Na2Ce2[BO2(OH)][BO3]2 · H2O with isolated boron triangles
Аннотация
Crystals of a new polar borate Na2Ce2[BO2(OH)][BO3]2 · H2O were prepared by hydrothermal synthesis. The crystals are orthorhombic, a = 7.2295(7) Å, b = 11.2523(8) Å, c = 5.1285(6) Å, Z = 2, sp. gr. C2mm (Amm2), R = 0.0253. The formula of the compound was derived from the structure determination. The Ce and Na atoms are coordinated by nine and six O atoms, respectively. The Ce position is split, and a small amount of Ce is incorporated into the Na1 site with the isomorphous substitution for Na. The anionic moieties exist as isolated BO3 and BO2(OH) triangles. The planes of the BO2(OH) triangles with mm2 symmetry are parallel to the ab plane. The planes of the BO3 triangles with m symmetry are perpendicular to the ab plane and are rotated in a diagonal way. The splitting of the Ce positions and the polar arrangement of the BO2(OH) triangles, water molecules, and Na atoms are observed along the polar a axis. The new structure is most similar to the new borate NaCa4[BO3]3 (sp. gr. Ama2), in which triangles of one type are arranged in a polar fashion along the c axis. Weak nonlinear-optical properties of both polar borates are attributed to the quenching of the second-harmonic generation due to the mutually opposite orientation of two-thirds of B triangles in the unit cell.
Structure of Organic Compounds
Preparation and analysis of multilayer composites based on polyelectrolyte complexes
Аннотация
A method for preparing multilayer film composites based on chitosan has been developed by the example of polymer pairs: chitosan–hyaluronic acid, chitosan–alginic acid, and chitosan–carrageenan. The structure of the composite films is characterized by X-ray diffractometry and scanning electron microscopy. It is shown that the deposition of a solution of hyaluronic acid, alginic acid, or carrageenan on a chitosan gel film leads to the formation of a polyelectrolyte complex layer at the interface, which is accompanied by the ordering of chitosan chains in the surface region; the microstructure of this layer depends on the nature of contacting polymer pairs.
Structure of Macromolecular Compounds
X-ray structures of uridine phosphorylase from Vibrio cholerae in complexes with uridine, thymidine, uracil, thymine, and phosphate anion: Substrate specificity of bacterial uridine phosphorylases
Аннотация
In many types of human tumor cells and infectious agents, the demand for pyrimidine nitrogen bases increases during the development of the disease, thus increasing the role of the enzyme uridine phosphorylase in metabolic processes. The rational use of uridine phosphorylase and its ligands in pharmaceutical and biotechnology industries requires knowledge of the structural basis for the substrate specificity of the target enzyme. This paper summarizes the results of the systematic study of the three-dimensional structure of uridine phosphorylase from the pathogenic bacterium Vibrio cholerae in complexes with substrates of enzymatic reactions—uridine, phosphate anion, thymidine, uracil, and thymine. These data, supplemented with the results of molecular modeling, were used to consider in detail the structural basis for the substrate specificity of uridine phosphorylases. It was shown for the first time that the formation of a hydrogen-bond network between the 2′-hydroxy group of uridine and atoms of the active-site residues of uridine phosphorylase leads to conformational changes of the ribose moiety of uridine, resulting in an increase in the reactivity of uridine compared to thymidine. Since the binding of thymidine to residues of uridine phosphorylase causes a smaller local strain of the β-N1-glycosidic bond in this the substrate compared to the uridine molecule, the β-N1-glycosidic bond in thymidine is more stable and less reactive than that in uridine. It was shown for the first time that the phosphate anion, which is the second substrate bound at the active site, interacts simultaneously with the residues of the β5-strand and the β1-strand through hydrogen bonding, thus securing the gate loop in a conformation
Crystallization and preliminary X-ray diffraction study of recombinant ribokinase from Thermus Species 2.9
Аннотация
Ribokinase from a thermophilic strain of Thermus species 2.9 belonging to the carbohydrate ribokinase family (EC 2.7.1.15) was isolated, purified, and crystallized. The crystallization conditions were found by the vapor-diffusion technique and were then optimized to apply the capillary counter-diffusion technique. The X-ray diffraction data set was collected from the crystals, which were grown by the counter-diffusion technique, at the SPring-8 synchrotron radiation facility to 2.87 Å resolution. The crystals belong to sp. gr. P1211 and have the following unit-cell parameters: a = 81.613 Å, b = 156.132 Å, c = 87.714 Å, α = γ = 90°, β = 103.819°. The X-ray diffraction data set is suitable for determining the three-dimensional structure of the protein by the molecular-replacement method.
Real Structure of Crystals
X-ray diffraction characterization of epitaxial CVD diamond films with natural and isotopically modified compositions
Аннотация
Comparative investigations of homoepitaxial diamond films with natural and modified isotopic compositions, grown by chemical vapor deposition (CVD) on type-Ib diamond substrates, are carried out using double-crystal X-ray diffractometry and topography. The lattice mismatch between the substrate and film is precisely measured. A decrease in the lattice constant on the order of (Δa/a)relax ∼ (1.1–1.2) × 10–4 is recorded in isotopically modified 13С (99.96%) films. The critical thicknesses of pseudomorphic diamond films is calculated. A significant increase in the dislocation density due to the elastic stress relaxation is revealed by X-ray topography.
Study of the nanosiderite from ferruginous quartzites of Kursk magnetic anomaly by transmission electron microscopy
Аннотация
Biogenic siderite consisting of equally crystallographically oriented disklike nanoparticles 5–20 nm in size has been found (using transmission electron microscopy) in oxidized ferruginous quartzites (jaspilites) of the Lebedinsky field of the Kursk magnetic anomaly. Based on microdiffraction data and highresolution images, lowering of the siderite structure symmetry from \(R\overline 3 c\) to \(R\overline 3 \) has been established for the first time. A siderite structure model is proposed to explain this fact. Within this model, vacancies formed as a result of oxidation of some part of Fe2+ cations to the Fe3+ state are ordered in one of two nonequivalent octahedral sites. Identical crystallographic orientation and nanoparticle morphology have been established for coexisting siderite and hematite. It is suggested that the revealed specific features of nanosiderite are related to its biogenic origin.
Surface and Thin Films
Neuromorphic elements and systems as the basis for the physical implementation of artificial intelligence technologies
Аннотация
The instrumental realization of neuromorphic systems may form the basis of a radically new social and economic setup, redistributing roles between humans and complex technical aggregates. The basic elements of any neuromorphic system are neurons and synapses. New memristive elements based on both organic (polymer) and inorganic materials have been formed, and the possibilities of instrumental implementation of very simple neuromorphic systems with different architectures on the basis of these elements have been demonstrated.
Electron microscopy study of the microstructure of Ni–W substrate surface
Аннотация
The surface microstructure of Ni–W alloy tapes, which are used as substrates to form films of high-temperature superconductors and photovoltaic devices, has been studied. Several samples of a Ni95W5 tape (Evico) annealed under different conditions were analyzed using scanning electron microscopy, energy-dispersive X-ray microanalysis, electron diffraction, and electron energy-loss spectroscopy. NiWO4 precipitates are found on the surface of annealed samples. The growth of precipitates at a temperature of 950°С is accompanied by the formation of pores on the surface or under an oxide film. Depressions with a wedge-shaped profile are found at the grain boundaries. Annealing in a reducing atmosphere using a specially prepared chamber allows one to form a surface free of nickel tungstate precipitates.
Domain structure and properties of triglycine sulfate crystals with profile D,L-α- and L-α-alanine-doped layers
Аннотация
A complex investigation of the domain structure and dielectric properties of triglycine sulfate (TGS) crystals containing profile layers doped with D,L-α-alanine (DLATGS) and L-α-alanine (LATGS) impurities is carried out. The images of the DLATGS and LATGS layers and ferroelectric domains are obtained by piezoelectric force microscopy; the parameters of the domain structure and the degree of unipolarity are determined. It is established that DLATGS layers are multidomain and LATGS stripes are mainly single-domain. The experimental data on the macroscopic dielectric properties of the crystals are compared with the results of a microscopic analysis of the domain structure.
Vapor phase epitaxy of CdTe on sapphire substrates in dependence on the vapor-flow orientation
Аннотация
The growth of cadmium telluride films on a structured (0001) sapphire surface oriented at an angle of 44° to the vapor-flow direction and normal to the steps formed along the \(11\overline 2 0\) direction is studied. It is found that this geometry of the vapor source and a substrate (heated to a temperature of 300°С) provides the growth of single-crystal CdTe films if a step height on the substrate surface is more than 1 nm. The results are explained by the occurrence of a longitudinal component of the diffusion flux of СdTe molecules and atoms toward the steps from the inner side and their high density at the step edge from the outer side due to the presence of the Ehrlich–Schwoebel barrier, which ensures the efficient supply of material and minimum supersaturation necessary for the nucleation at the step edge and growth of oriented CdTe islands. The cadmium telluride films that are grown have the \(\left( {110} \right)\left[ {1\overline 1 0} \right]CdTe\left\| {\left( {0001} \right)} \right.\left[ {11\overline 2 0} \right]A{l_2}{O_3}\) orientation and a composition similar to stoichiometric CdTe.
Nanomaterials and Ceramics
Experimental and theoretical study of the transport of silver nanoparticles at their prolonged administration into a mammal organism
Аннотация
The transport of silver nanoparticles in the organism of laboratory animals has been investigated. A mathematical model of the biokinetics of prolonged administration of nonmetabolizable and nonaglomerating pharmaceutical preparations is proposed, and its analytical solution is found. Based on the experimental data on the prolonged introduction and excretion of colloidal silver nanoparticles and the numerical approximation of the solutions to the equations for the proposed model, time dependences of the silver mass content in brain and blood are obtained and some other important biokinetic parameters are determined. It is concluded that both chronic1 and subchronic2 peroral application of these nanoparticles as an biologically active additive or antiseptic is potentially dangerous.
Crystal Growth
Study of the K2Ni(SO4)2 ∙ 6H2O–K2Co(SO4)2 ∙ 6H2O–H2O diagram and determination of the conditions for growing K2(Ni,Co)(SO4)2 ∙ 6H2O mixed crystals
Аннотация
The phase diagram of the K2Ni(SO4)2 · 6H2O–K2Co(SO4)2 · 6H2O–H2O ternary system is investigated in the temperature range of 30–70°С, and a relationship between the compositions of the equilibrium phases of the K2CoxNi(1–x)(SO4)2 · 6H2O (KCNSH) solid solution and the growth solution is established. It is shown how the salt compositions of the liquid and solid phases change during crystal growth upon slow cooling of solution. A dependence of the lattice parameters of the KCNSH solid solution on the concentration of isomorphic components is experimentally found.
Growth of LiNbO3:Er Crystals and concentration dependences of their properties
Аннотация
A series of lithium niobate (LiNbO3) crystals of congruent and stoichiometric compositions, doped with erbium, have been grown under non-steady-state thermal conditions. A series of LiNbO3:Zn crystals, nominally pure LiNbO3 crystals of congruent and stoichiometric compositions, and a LiNbO3:B crystal have also been grown. Both growth conditions and concentration dependences of physicochemical, ferroelectric, and structural characteristics of LiNbO3:Er crystals are investigated. The growth regular domain microstructures and periodic nanostructures in LiNbO3:Er crystals are analyzed by optical microscopy and atomic force microscopy (AFM). A comparative study of the optical homogeneity and photorefractive properties of LiNbO3:Er crystals of congruent and stoichiometric compositions and the Raman spectra of LiNbO3 crystals of different compositions is performed.