Problems and prospects of development of nanomembrane technology

The latest Russian and foreign studies devoted to the theoretical and experimental investigation of the processes of formation of porous structure of track nanomembranes, the methods for studying their properties, and the application of track membranes to synthesis of nanostructures by a template method are reviewed. The results of the investigations carried out in these promising directions at the Department of Membrane Technologies of the Shubnikov Institute of Crystallography, Russian Academy of Sciences, are also presented. On the basis of the theoretical investigations of the mechanism of interaction of high-energy ions with a solid, it is shown that the theory of instantaneous explosion in a track region must be carefully verified. The results of the experimental investigation of the structure of tracks of high-energy ions in a polymer and the mechanism of pore formation in the stage of chemical etching of tracks showed that the track structure is inhomogeneous in the radial direction. It is shown that the surface of polyethylene terephthalate track membranes becomes negatively charged in neutral and alkaline solutions, and the value of this charge depends on the pore diameter. Good prospects of application of secondary metal structures formed on the basis of track membranes in mass spectroscopy are demonstrated experimentally.     

Optimization of the local crystallization processes of preparing chiral drugs in periodic crystallizers

The regularities of periodic processes of local crystallization of enantiomers and the kinetics of nucleation and growth of crystals are considered. The criteria for optimization of technological processes of preparing chiral drugs with the aim of attaining the maximum yield of final products with a required optical purity are formulated on the basis of experimental data.     

蒙特卡罗模拟金刚石薄膜化学气相沉积过程中甲烷浓度的影响

本工作采用蒙特卡罗模拟,研究了以CH4/H2气体混合物作为源料气体的电子辅助热丝化学气相沉积中甲烷浓度对气相沉积过程的影响.计算了典型实验条件下电子能量分布,研究了电子平均能量、碎片H及CH3数目的空间分布、H与CH3的比值及CH3携带的能量随甲烷浓度的变化.结果表明:当电子能量为2-3eV时,电子的数密度达到一峰值;平均电子能量随着甲烷浓度的增加而增加;电子与气体分子碰撞产生的碎片H、CH3和CH2的数密度随距热丝的距离而变化;随着甲烷浓度的增加,原子氢H的数目缓慢下降,然而,官能团CH3和CH2的数目缓慢上升;H与CH3的数量比随甲烷浓度的增加而减少;碎片CH3携带的能量处于1～5eV范围之内,且当甲烷浓度为1.3;时,该能量达到一最值.     

Methods of crystal optics for studying electromagnetic phenomena in metamaterials: Review

The state of the art of electrodynamics of new composite media—metamaterials—is reviewed. The composites in the form of a periodic lattice of identical elements, which are in essence artificial crystals with characteristic scales of the internal structure from several centimeters to several hundred nanometers are considered. The most important properties of metamaterials and the specific features of propagation of electromagnetic signals in these media are described. Particular attention is paid to the conventional methods of condensed-matter physics, which have found application in the electrodynamics of metamaterials and have provided dynamic development of this new field of science and technology.     

Plasma‐enhanced chemical vapor deposition of 99.95% 28Si in form of nano‐ and polycrystals using silicon tetrafluoride precursor

The process of plasma chemical deposition of silicon was investigated from its tetrafluoride containing 99.99% of ²⁸Si isotope in the form of thin layer of nano‐crystalline silicon on silicon substrate and of thick layer of polycrystalline silicon on the inner surface of quartz reactor. The layers are characterized by the methods of X‐ray diffraction and Raman spectroscopy. Using the SIMS method the mechanism of isotopic dilution was investigated in the PECVD process (the content of ²⁸Si isotope in layers was 99.95‐99.98%). A necessity is indicated in thorough special preparation of the reactor for minimization of isotopic dilution in case of fabrication of silicon containing ≥99.9% of ²⁸Si. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The review of possible interrelations between ionic conductivity, internal friction and the viscosity of glasses and glass forming melts within the framework of Maxwell equations

The review contains the results of application of Maxwell equations for mechanical relaxation and electrical conductivity, to the systematization of large amount of experimental data related to mechanical, viscous, and electrical properties of inorganic glasses and glass forming melts. The generalization of internal friction results shows the existence of characteristic values for the ratios of temperatures, responsible for α-, β- and ionic relaxations; they are independent on the frequency and chemical composition. This is the evidence for the main role of elastic deformations at various corpuscular processes and the existence of characteristic scale of activation barriers predetermined by local volumes of deformation. It is shown the possibility of very precise calculation of the temperature of “ionic” internal friction maximum for one-alkali oxide glasses directly from Maxwell equation and d.c. conductivity experimental data. The volumes of particles overcoming the potential barrier at viscous flow practically coincide with the results of direct structural determinations. The existence of universal relation between d.c. conductivity and viscosity for the extremely wide temperature intervals (Littleton relation) is proved for silicate and phosphate melts. The theory of this dependence is proposed. The results show the effectiveness of the attempts to unite the continual and discrete approaches within the framework of Maxwell equations to obtain the simplest understanding the mechanisms of different types of relaxation. The review comprises many Russian papers unknown in English scientific literature.     

The influence of crystalline anisotropy on the evolution of the crystallization front during directional solidification

The evolution of the crystallization front of transparent crystals of succinonitrile and pivalic acid in the course of directional solidification in the field of a temperature gradient (Bridgman method) is investigated experimentally. The influence of crystalline anisotropy is examined using single crystals of different orientations. Bulk (cylindrical) and planar single crystals of the materials under investigation are studied and compared for the first time. It is established that the crystallographic direction of growth plays an important role and determines the structure of the crystallization front at different stages of its evolution. New manifestations of the dynamic effects responsible for the development of the nonstationary periodic structure are revealed.     

Effect of nonstoichiometry and technological impurities on the structural properties and absorption of Y3F5O12 crystals in the IR range

Complex studies of the optical and structural properties and the elemental composition of a series of yttrium iron garnets (YIG) grown from flux have been performed with due regard for the crystallographic orientation of the platelets. It has been established that the presence of Mn, Ba, and V microimpurity ions at a level of a few thousandths of a percent can play a stabilizing role in the synthesis of perfect crystals with the garnet structure. The criterion of the quality of the grown crystals is formulated as the ratio of the total number of Y and Fe cations to the number of oxygen anions (in wt %).     

High-resolution transmission electron microscopy for crystallographic study of nanomaterials

The potential of high-resolution transmission electron microscopy (including the quantitative computer processing of images and computer simulation) in a local analysis of nanomaterials is discussed. A number of examples of the application of fast Fourier transform and simulated high-resolution electronmicroscopy images in the identification of nanophases and the crystallographic study of nanocrystals and nanoparticles are considered. The role that B.K. Vainshtein played in the development of a unified approach for determination of the structure of materials using short-wave diffraction is indicated.     

Manifestation of optical activity in crystals of different symmetry classes

Specific features of manifestation of optical activity in cubic, uniaxial, and biaxial crystals are described. The effect of optical activity on characteristics of transmitted light is considered as a function of the wavelength of incident light, temperature, and the orientation the optical axis. The results of the investigation of crystals of different symmetry classes are reported.     

Dielectric investigations of organic–inorganic hybrid based on (2-hydroxypropyl) cellulose with nanosheet crystallites of quasi-TiO2

In this paper, dielectric spectroscopy investigations of organic–inorganic hybrid composite obtained from (2-hydroxypropyl)cellulose (HPC) with nanosheet crystallites of quasi-TiO₂ are presented. This hybrid belongs to the class of composites, which have no covalent bonds between organic and inorganic constituents and the behaviour of composite is determined mainly by interface of two constituents. The analysis of the molecular dynamics of the hybrid system reveals the influence of the nanosheet crystallites of quasi-TiO₂ on the relaxation processes of HPC matrix. The relaxation strength of γ process strongly increases in composite as compared to neat HPC. A shift to higher temperature has been evidenced in the case of α and β processes. A higher value of the slope of the maximum frequency vs. the inverse temperature for the α-relaxation of the composite has been observed. At high temperatures the mesomorphic behaviour of HPC has been drastically reduced in the composite. The results of our investigations are interpreted in terms of a presence of intermolecular forces between HPC and nanosheet crystallites of quasi-TiO₂.     

Study of nanostructured materials by optical and photoelectron spectroscopy

The results of investigations of the electronic energy structure and physicochemical properties of nanostructured systems by optical and photoelectron spectroscopy using synchrotron radiation are briefly reviewed. The quantum-size effect in thin metal films and surface lateral superlattices are analyzed. The effect of structural defects on the chemical state of metal clusters on the surface of oxides in catalytically active systems is discussed. The results of the study of the specific features of chemical bonding in solid-state nanostructures within the quasi-molecular approach are presented. The possibility of using biological structures (proteins) as matrices for the formation of ensembles of nanoclusters is considered.     

Scaling in the Optical Characteristics of Aperiodic Structures with Self-Similarity Symmetry

The properties of diffraction gratings and multilayered systems constructed using 1D models of quasicrystals are considered based on numerical simulation. It is shown that there is a direct relationship between the self-similarity symmetry of quasicrystals and scaling in the characteristics of the above-mentioned optical devices. The degree of structural correspondence between the graphical representations of the geometric properties of crystals, light diffraction patterns of gratings, and the transmission spectra of multilayered systems is estimated. It is shown that certain types of self-similarity symmetry make the characteristics of aperiodic diffraction gratings highly stable to a change in the size ratio of forming elements.     

Precise calculations in simulations of the interaction of low energy neutrons with nano-dispersed media

We discuss properties of the interaction of slow neutrons with nano-dispersed media and their application for neutron reflectors. In order to increase the accuracy of model simulation of the interaction of neutrons with nanopowders, we perform precise quantum mechanical calculation of potential scattering of neutrons on single nanoparticles using the method of phase functions. We compare results of precise calculations with those performed within first Born approximation for nanodiamonds with the radius of 2–5 nm and for neutron energies 3 × 10^-7–10^-3 eV. Born approximation overestimates the probability of scattering to large angles, while the accuracy of evaluation of integral characteristics (cross sections, albedo) is acceptable. Using Monte-Carlo method, we calculate albedo of neutrons from different layers of piled up diamond nanopowder.     

Geometrical laws in inorganic chemistry

On the basis of an original interpretation of the crystal state, it is shown that most of the structural types are determined by a small set of planar nets densely filled with the heaviest atoms of the structure. These nets are combined into atomic sublattices (matrices of the structure types) by the operations of (pseudo) symmetry, thus reducing the number of the degrees of freedom in the structure, which, in turn, provides structure stability. It is shown on examples of heavy-cation oxides, fluorides, and sulfides that the number of the types of such matrices (F-, I-, etc.) is limited. Each type is characterized by a certain structure-determining complex of mutually intersecting crystallographic planes parallel to the most densely filled atomic nets. Most of the atomic nets considered in crystal chemistry are, in fact, various sections of the sublattices-matrices formed by a limited number of densely filled atomic nets.     

Nanostructures on the Basis of Porous Alumina with Intercalated with Cholesteric Liquid Crystal

The introduction of liquid crystal materials into the porous material host will help us to get optically active nanocomposites. Nanocomposite based on aluminum oxide host with cholesteric liquid crystal is characterized by a shift of bandwidth wavelength minimum. In case of intercalation of cholesteric liquid crystals into the pores of aluminum oxide host the shift of transmittance minimum into the short wave region are observed. We analyzed the ways, which indicate the deformation of the pitch of the cholesteric helix and showed the role of capillary forces in the deformation of the pitch of cholesteric liquid crystal.     

Possible dynamical mechanism of dislocation drag in metals in the easy slip stage

The slip of an edge dislocation through a system of parallel immobile dislocation dipoles oriented parallel to it has been investigated. A new mechanism of dislocation drag (irreversible transformation of the kinetic energy of a moving dislocation into the energy of natural vibrations of a pair of edge dislocations (forming a dipole), excited by the elastic field of the moving dislocation) is proposed and analyzed. The dynamic drag force of moving dislocation caused by this mechanism is calculated. It is shown that this force is inversely proportional to the slip velocity of mobile dislocations.     

Structural properties of liquid Fe-Si alloys

The atomic structure of liquid Fe-Si alloys within the whole concentration range (including pure components) was investigated at the temperature of 1550 °C by means of X-ray diffraction. Analysis of the reported data on physical properties of Fe-Si melts has been carried out. Interrelation between liquid-state structure and solid-state properties was considered. Fe-Si alloys in the liquid state are shown to be micro-inhomogeneous and they contain atomic micro-formations (clusters) that differ by atomic composition and packing. There are five types of clusters: two of them consist of atoms of one kind (Fe or Al); the composition of the other clusters depends on the stoichiometry of solid Fe₃Si, FeSi and Fe₂Si₅ phases. The entire concentration range of the Fe-Si system consists of four concentration intervals. Within each interval melts are constituted of the clusters of two kinds. The variation of the component concentrations in Fe-Si alloys results in changing of volume fraction of each type clusters, whereas the atomic composition and arrangement inside the clusters remains constant.