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.     

Liquid phase epitaxy of AlxGa1–xAs-GaAs heterostructures

This paper is concerned with the investigation of the peculiarities of the application of liquid phase epitaxy for obtaining multilayer structures with heterojunctions in the AlAs–GaAs system. Segregational depletion of Al in liquid and in solid phases is characteristic of this system. It is proved that supercooling of the substrate and numerous inclusions of Al allow to decrease this segregational depletion of Al and to obtain layers of nearly constant composition up to 600 μm in thickness. A new technique of crystallization of structures from a limited volume of melt with the change of solutions by way of compulsory squeezing out of the foregoing solution by the following one is put forward with the view to perfect the planarity of multilayer structures with abrupt heterojunctions and to improve the complete change of solutions on a substrate. The results of the study of various methods of controlling the value and direction of the Al concentration gradient are listed. It has been proved that structures with fluent increase of Al concentration during the crystallization process and also structures with alteration in the gradient direction of Al concentration may be obtained by way of artificial slowing down or acceleration of the process of mixing up solutions of various compositions.     

Brittle fracture of single crystals and active structure of cleavage surfaces

By the method of vacuum decoration at an electronmicroscopic scale with the use of lowangle electron diffraction the dependence of brittle fracture of alkali halide crystals and of the active structure of cleavage surfaces on the character of ordered distribution of point defects in crystals has been studied. The occurrence of cleavage steps reflects the presence in crystal volume, where brittle fracture took place, of a high degree of periodicity of point defects mainly in one crystallographic direction. The smooth areas of the cleavage surface reflect the existence in these places of a periodic distribution of point defects in two mutually perpendicular crystallographic directions. Coincidence of periods between the cleavage steps with the periods in the arrangement of point defects on smooth areas of the cleavage surface allows the steps to be regarded not only as elements of the geometric microrelief but primarily as electrically active linear elements of the crystal surface, reflecting the linear arrangement of point defects. Together with cleavage steps exhibiting a stable in time activity there arise cleavage steps with an extremely high, but rather shortlived activity being the consequence of the brittle fracture process proper. The electrically active linear elements of the point defect lattice – linear elements of the potential relief of the surface – play a most important role in heterogeneous processes, in particular crystallization processes.     

Profile-sapphire and its structural perfection

The paper is concerned with the growing of sapphire of various profiles and with the investigation of its structural perfection. It is shown that the kind of the crystallographic forms and the dislocation structure essentially depends on the degree of overheating of the melt. Near the surface of profiled crystals wide dislocation-free zones (upto 200 μm) may be obtained. A dependence of the length of the mosaic block boundary on the rate of growing can be observed. A high ratio of the area of the radiating surface to the crystal volume gives the possibility of a rapid growing of profile crystals.     

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.     

Verfahren und Vorrichtung zur Bestimmung von Krümmungen einkristalliner,scheibenförmiger Körper

With the production of semiconductor devices the problem of bending of monocrystalline slices occurs, these being an expression of the reduction of the crystal perfection, increasing with each working step during the technological process. Thus the determination of the bend can give an information on the influence of each working step on the internal stresses of the crystalline body. A procedure is described which takes advantage of the Bragg reflection of an X-ray beam in the lattice planes of the crystal, in order to determine the inclination of the plane. A design is presented based on this procedure permitting a high degree of automation.     

X-ray studies of biological macromolecules at the Shubnikov Institute of Crystallography of the Russian Academy of Sciences

The results of X-ray diffraction studies of a number of proteins and the carnation mottle virus performed over a period from 1970 to 2000 at the laboratory created by Academician B.K. Vainshtein at the Shubnikov Institute of Crystallography of the Russian Academy of Sciences are surveyed. The fundamental principles of the spatial organization of protein structures are considered. The characteristic features of the three-dimensional structures of a number of various proteins performing various functions are discussed including leghemoglobin, catalases, pyrophosphatases, pyridoxal-dependent enzymes, nucleotide depolymerases, proteases, and plant toxins. The results obtained for carnation mottle virus are summarized. The contribution of X-ray diffraction studies to the understanding of mechanisms of functioning of the above macromolecules and the first stages of the crystallographic studies of nucleic-acid fragments are discussed. The present state and the prospects of studies of three-dimensional structures of macromolecules are also considered.     

Three-dimensionality of space in the structure of the periodic table of chemical elements

The effect of the dimension of the 3D homogeneous and isotropic Euclidean space, and the electron spin on the self-organization of the electron systems of atoms of chemical elements is considered. It is shown that the finite dimension of space creates the possibility of periodicity in the structure of an electron cloud, while the value of the dimension determines the number of stable systems of electrons at different levels of the periodic table of chemical elements and some characteristics of the systems. The conditions for the stability of systems of electrons and the electron system of an atom as a whole are considered. On the basis of the results obtained, comparison with other hierarchical systems (nanostructures and biological structures) is performed.     

Formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet grown by horizontal directed crystallization method

It is shown that the formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet (YAG) grown by the method of HDC is caused by local accumulation of impurities, disturbance of morphological stability of the crystallization front and capture of inclusions and impurities in the nodal region of the melt two‐vortex convection. Studied is the influence of thermal and geometrical parameters of the melt and the shape of the crystallization front on the conditions of the formation of the capture of inclusions.     

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 %).     

Change of the Normal Rate of Hills Growth on the (001) Face of TGS Single Crystal Under Constant Crystallization Conditions

Considerable change (up to 100% in one of the cases) of the normal growth rate of hills on the (001) face of the TGS crystal at strictly constant supersaturation and temperature is registered experimentally. On the basis of the spatial disposition of the dislocations, which form the source of the steps, a model of a growth centre (called herein non-parallel centre of growth) is proposed. The model is qualitatively concordant with the experimental data. It is shown that the inconstancy of the normal rate of growth at constant supersaturation and temperature is an immanent characteristic of the non-parallel centre of growth.     

On the theory of two-dimensional nucleation on a structureless substrate. Effect of supersaturation

The work of formation of two-dimensional nuclei of the (100), (110), and (111) faces of crystal with simple cubic lattice on a structureless substrate was calculated. The simplification of the equilibrium form with increasing supersaturation was taken into consideration. At low supersaturations the formation of nuclei of the (100) face alone is possible. With increasing supersaturation the appearance of two-dimensional nuclei of the other two faces becomes possible. The probability of their formation increases but never exceeds the probability of the formation of two-dimensional nuclei of the (100) face. There exists a limiting supersaturation above which the work of formation of two-dimensional nuclei of the three kinds of faces becomes equal to zero.     

Study of a Surface Layer of Calomel Monocrystals by the Method of Plastmatic Etching

The method of plasma (ionic) etching provides information on both the degree of damage and the real structure of a treated surface of a cleavage crystallographic plane (110). The altered surface structure of this plane, which is due to cutting, grinding and polishing, is a cause of a rapid loss of calomel at the beginning of the etching process. The minimum loss rate is directly proportional to the thickness of the damaged surface. The ensuring rapid loss of calomel is due to an increased ruggedness of the surface. The ionic etching of calomel on the crystallographic plane (110) proceeds in six phases which are documented in photographs. The method of ionic etching is promissing for a high-quality treatment of surfaces of calomel acousto-optical functional elements designed for connections with ultrasound transducers.