Features of the magnetic state of the layered Fe-V nanostructure of the superconductor-ferromagnet type

The magnetic state of the V(39 nm)/20 [V(3 nm)/Fe(3 nm)] nanostructure has been investigated by polarized neutron reflectometry in the temperature range from 1.6 to 30 K in magnetic fields from 0.2 to 15 kOe. The data obtained indicate that the superconductivity of vanadium layers may affect magnetic ordering both over the depth of the structure and in its plane.     

Analysis of the applicability of the modified kinematic approximation to describe the off-specular neutron scattering from the surface of micro- and nanostructured objects

The applicability of the modified kinematic approximation to describe the off-specular neutron scattering from interfaces between media is analyzed. It is demonstrated that in some cases one can expect not only a qualitative but also a quantitative agreement between the data and the results of experiments and calculations based on more accurate techniques. Diffuse scattering from rough surfaces and thin films with correlated and noncorrelated roughness of the upper and lower interfaces and the neutron diffraction by stripe magnetic domains and magnetic domains with a random size distribution (magnetic roughness) are considered as examples.     

Kinetics of the photoinduced evolution of the nanostructured porous silicon photoluminescence

In this work we show that the illumination level used during porous silicon preparation is a key factor determining the subsequent photoinduced evolution of the photoluminescence spectra. The post-preparation evolution results from the combination of at least two effects. One of them is ruled by the size changes of the silicon nanostructure due to photo-oxidation, and dominates for samples prepared under low illumination levels. On the other hand, for samples prepared under high illumination levels the post-preparation evolution is dominated by a quenching effect, resulting from photoinduced dangling bonds generation in the hydrogen-rich surface of the nanostructure. The kinetics of dangling bond creation is similar to that found in the Staebler–Wronski effect for hydrogenated amorphous silicon.     

Understanding the effect of solvent polarity on the habit modification of monoclinic paracetamol in terms of molecular recognition at the solvent crystal/interface

The habit change of monoclinic paracetamol crystallized from solutions with different solvents such as water, ethanol, methanol, acetone, isopropyl alcohol, tetrahydrofuran, cyclohexanone, acetonitrile and 1, 4 ‐ dioxane was investigated. Change in solubility, pH and nucleation time of paracetamol in these solvents at ambient condition was studied. The polymorphic form of the nucleated paracetamol was observed under in‐situ optical microscopy. Solutions with different solvents having different chemical nature and polarity yielded paracetamol crystals with different habits: columnar morphology from polar protic water and prismatic morphology from other selected polar protic, aprotic and in non‐polar solvents. The significant differences on the growth rate of various crystal habit faces of the monoclinic paracetamol grown from different solvents are attributed in context with the solubility of the solute, solvent polarity, evaporation number of the solvent, rate of generation of supersaturation and the role of hydrogen bonding interaction between the solvent molecules and protruding solute molecules on the crystal surface. Among the solution with different solvents, bulk monoclinic paracetamol single crystal was grown from ethanolic solution using seed rotation technique by controlled cooling method.     

On the capability of revealing the pseudosymmetry of the chalcopyrite‐type crystal structure

The tetragonal crystal‐structure type of chalcopyrites (chemical formula A^IB^IIIC^VI₂) is a superstructure of sphalerite type. The c /a ratio differs generally from the ideal value 2, i.e., the crystal structure is pseudocubically distorted. For CuInSe₂ and CuGaSe₂ thin films, simulations demonstrate that it is theoretically possible to reveal the tetragonality in electron backscatter‐diffraction (EBSD) patterns for CuGaSe₂, whereas it may not be possible for CuInSe₂. EBSD experiments on CuGaSe₂ thin films using the ”Advanced Fit” band‐detection method show that it is possible to extract accurate misorientation‐angle distributions from the CuGaSe₂ thin film. Pole figures revealing the texture of the CuGaSe₂ thin film are shown, which agree well with X‐ray texture measurements from the same layer. (© 2008 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the conductivity of the lithium borosilicate glass system

The lithium borosilicate system (Li₂O)_0.4(B₂O)_(0.6x)(Si₂O₄)_0.6(1−x) with x = 0, 0.2, 0.3, 0.4, 0.6, and 0.8 was investigated using impedance spectroscopy. Impedance spectra were taken in the frequency range from 50 Hz to 1 MHz and in the temperature range from 100 to 280 °C. The ac- and dc-conductivity, relaxation frequency and activation energy of the dc-conductivity were extracted from the impedance spectra. The dc-conductivity of the investigated glass samples increases almost linearly from silica rich (x = 0) to the boron rich (x = 0.8) samples. Activation energy (E_a) was found to be 0.65 eV for high conducting sample and 0.8 eV for low conducting sample, respectively. The mixed glass-former effect was not observed on the samples studied. The effect of temperature scaling of ac-conductivity was observed, which indicates, that ionic conductivity relaxation mechanism is temperature independent for samples with x = 0, 0.2, 0.3. However, some deviations from scaling were found for the samples with higher x (x = 0.4, 0.6, 0.8).     

The effect of the H2O/TEOS ratio on the structure of gels derived by the acid catalysed hydrolysis of tetraethoxysilane

Silica gels were produced by the acid catalysed hydrolysis of tetraethoxysilane (TEOS) using H₂O/TEOS ratios from 2 to 50. After heat treatment the structure of the gels was studied using nitrogen adsorption, small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and bulk density measurements.All the gels possessed microporosity in the region of 30 Å or less. For H₂O/TEOS = 25 and 50 the matrix density was found to be uniform, but for gels from solutions with H₂O/TEOS = 2,4 and 10, density fluctuations in the matrix were detected from Porod analysis of the SAXS data. These results indicate that in higher water content solutions, rearrangement of the polymeric chains leads to small densified particles, but for lower water content solutions, gelation results from the entanglement of linear chains leaving free volume on a molecular scale between the chains.     

On the 70th anniversary of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences

We are celebrating the 70th anniversary of the Shubnikov Institute of Crystallography. The institute has gone from being a small laboratory of piezoelectric crystals to a large internationally known scientific center. The 1990s was a decade of ruin, both literally and figuratively, for our institute; however, it is hard to believe that was the case when walking through the corridors of the institute today.     

On the role of the porous shell of the solid core of the earth in the anomalous heat and mass flow to the mantle

The model of the pressure-induced first-order phase transition of a metal melt to the metallicglass state considers a thermodynamically nonequilibrium porous near-surface shell of the solid core of the Earth, which contacts cyclonic vortices in the liquid core. Anomalous flows of heat and light-material mass to the mantle from the solid core at these contact points are calculated. These anomalous flows are shown to be comparable with the observed ones under the assumption of a rapid increase in the melt viscosity at pressures of 1–10 Mbar, which is characteristic of a solid core. In this case, the porous layer permeability may be very low.     

Efficiency of the focusing channel of the Belok Station in the Sibir-2 storage ring

The efficiency of the focusing systems of the Belok station on the synchrotron radiation beam from the bending magnet in the Sibir-2 storage ring has been experimentally determined using the IK-12 and IK-30 miniature ionization chambers developed at the Shubnikov Institute of Crystallography and calibrated with an FDUK-100UV photodiode developed at the Ioffe Physical Technical Institute.     

Effects of the Substrate Crystals upon the Structure of Thermal Oxide Layers on Si

Comparisons of Bragg reflections from thermal oxide thin films on Si wafers were made for five sets of samples with various kinds of substrates. The intensities of the reflections for the samples with the substrate of better quality were stronger than those of poor one, indicating that the structures of the crystalline SiO₂ in the oxide layer were related with the quality of the Si substrates. It is also shown that no diffraction peaks were observed from the oxide layers grown on Si substrates by chemical vapor deposition.     

硅基片上异质外延SiC的机理研究

本文利用低压高温MOCVD系统,成功地在Si(111)基片上外延出了具有高质量的SiC薄膜,并对其反应机理做了一些初步的研究.大部分观点认为,SiC/Si的异质外延,其最初的状态应该为Si衬底中Si的扩散.但是,本文通过在不同流量比的条件下,SiC薄膜在Si基片以及Al2O3基片上外延的比较,发现在SiC/Si的异质外延过程中起重大作用的并非Si衬底中Si的扩散,而是很大程度上作用于C向Si衬底的扩散.同时,还发现反应速率的快慢受SiH4流量所限制.当SiH4流量增加时,反应速率会明显加快,但是结晶质量会相对变差.     

On the inhomogeneity of the transition surface layer of the solid core of the earth

Different geophysical data and conclusions of theoretical models, which can give information about the behavior of the solid and liquid cores of the Earth as well as about the existence of a transition layer as a temperature-hysteresis region at a relatively weak first-order phase transition, are compared. It is concluded that liquid inclusions inevitably exist in this region; these inclusions are involved (due to the complex convective processes occurring in the liquid core) in the transport of light materials from some areas of the solid-core surface. The porosity and permeability of the transition layer determine the seismic acoustic inhomogeneities in these areas, which contact the convective flows in the liquid core. In particular, this explains the well-known ??east-west?? effect. Obviously, the model of the crystalline core is not the only possible alternative for a model of a core with a metallic glasslike structure.     

Study of X-ray diffraction from a surface acoustic wave in the grazing geometry with allowance for the curvature of the unperturbed crystal surface

Fresnel X-ray diffraction from a concave crystal surface in the presence of a surface acoustic wave (SAW) has been considered for grazing angles of incidence in noncoplanar symmetric Laue geometry. It is shown that the main peak and diffraction satellites are focused at different distances from a crystal. The effect of deviation from the Bragg angle, the spectral line width, and the SAW amplitude on the X-ray diffraction pattern has been analyzed. It is established that the contrast of an X-ray diffraction pattern of an SAW in Bragg-Laue grazing geometry is related to the character of irregularities of the crystal surface, and the pattern details depend on the measurement mode. The sensitivity of the method is about a nanometer. The focal image of the SAW serves as a scale landmark for determining the crystal surface characteristics.     

The Provenance Study of the Raw Materials of the Ancient Terracotta Found near the Crimean Bridge: Natural-Science Approach

Crystallography Reports - The paste of a series of ceramic products from the Black Sea and Mediterranean regions have been studied at the National Research Centre “Kurchatov Institute”...     

The fiftieth anniversary of the liquid crystal display

ABSTRACT

A record is given of the special meeting organised by the UK&I Chapter of the Society of Information Display held at the Royal Academy of Engineering in London, to celebrate the 50th anniversary of the RCA announcement of the first Liquid Crystal Display on 28th May 1968. Coming exactly eighty years after the report of the first liquid crystal materials, this announcement sparked interest across the globe, and particularly in the UK, Switzerland and Japan. Presentations of the early LCD history from Hilsum, Schadt and Raynes give insights into both the science and also the process of invention itself. These early contributors are followed by a view from the USA from Bos and representation from the companies Sharp and Merck that helped shape the success of these fascinating and useful materials. Also reviewed are talks on the use of organic semiconductors to drive plastic LCD by Sirringhaus, reflective LCD of Folium Optics, retail signage of Displaydata, as well as a look to the future from LCD competitors from Bodle (Phase Change Material displays) and BOE (OLED).     

Influence of Curing Frequency on the Morphology and the Electro-Optical Property of Polymer-Stabilized Cholesteric Textures

The effect of curing frequency on the morphology of polymer networks and the electro-optical property of normal-mode polymer-stabilized cholesteric textures (PSCTs) has been investigated. The scanning electron microscopy indicates that the shape of polymer networks transforms from honeycomb-like to fiber-like due to the increased solubility of the monomer at higher curing frequencies. The PSCTs cured at lower frequencies with sufficiently large network voids show a two-stage reorientation process that correlates with two kinds of cholesteric liquid crystal (LC) under different environments. The threshold voltage decreases as the curing frequency increases from 1 Hz to 10,000 Hz, while the field-off response time increases.     

On the dependence of the surface tension at the crystal-melt interface on the impurity concentration

The stationary task of impurity diffusion in a melt has been solved within a two-dimensional crystallization model in a second-order approximation with respect to the amplitude of deviation from a smooth crystallization front. The dependence of the surface tension Γ at the interface on the impurity concentration C is taken into account in the form Γ = Γ₀ + ζ _d C, where Γ₀ and ζ _d are constants. The variational method is used to obtain the condition for the transition from a smooth crystallization front to a cellular one. It is shown that calculated cell sizes are in agreement with the experimental data in the literature only when the parameter ζ _d ≠ 0. For binary systems with distribution coefficients k < 1 and k > 1, ζ _d should be positive and negative, respectively.

     

Scaling of the local dynamics and the intermolecular potential

The experimental fact that relaxation times, τ, of supercooled liquids and polymers are uniquely defined by the quantity TV^γ, where T is temperature, V specific volume, and γ a material constant, leads to a number of interpretations and predictions concerning the dynamics of vitrification. Herein we examine means to determine the scaling exponent γ apart from the usual superpositioning of relaxation data. If the intermolecular potential can be approximated by an inverse power law, as implied by the TV^γ scaling, various equations are derived relating γ to the Grüneisen parameter and to a common expression for the pressure derivative of the glass temperature. In addition, without assumptions, γ can be obtained directly from pressure-volume-temperature data. These methods for determining γ from molecular or thermodynamic properties are useful because they enable the P- and V-dependences of τ to be obtained, and thereby various analyses of the dynamics to be explored, without the need to carry out relaxation measurements beyond ambient pressure.     

Study of liquid crystals at the institute of crystallography

The history of studying liquid crystal at the Shubnikov Institute of Crystallography is briefly reviewed. The scientific results of researchers from the institute (starting from the 1960s and leading to the formation of a new field of science: physics of liquid crystals) are presented. In particular, it is shown how the physics of electro-hydrodynamic instability was developed in the 1970s. The origin of the physics of photonic crystals is considered. The discovery of the ferroelectric properties of ultrathin films of polar molecules is described. A breakthrough in the molecular theory of ferroelectricity in liquid crystals in the new century is discussed. The entire abundance of liquid-crystalline phases and processes occurring in them is estimated. An analysis of the participation of researchers from the Institute of Crystallography in the development of liquid-crystal science demonstrates their valuable contribution, which offers perspectives of new studies in this field.