Intensities Of X-ray Reflections Research Articles

One-Stage Synthesis of Microporous Carbon Adsorbents from Walnut Shells—Evolution of Porosity and Structure

One-stage synthesis technology for preparing carbon adsorbents with tailored porosity from agricultural waste is worthwhile due to their extensive application value. Thermal gravimetric analysis, low-temperature N2 adsorption, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and Raman spectroscopy were used to record the structure transformations of carbon materials, namely pore development, proceeding in the course of the step-wise pyrolysis of renewable and low-cost raw materials such as walnut shells (WNSs), which was carried out within a temperature range of 240–950 °C in a CO2 flow. The minimum threshold carbonization temperature for preparing nanoporous carbon materials from WNSs, determined by the examination of the N2 adsorption data, was 500 °C. The maximum specific micropore volume and BET surface achieved in the process without holding a material at a specified temperature were only 0.19 cm3/g and 440 m2/g, respectively. The pyrolysis at 400–600 °C produced amorphous sp2 carbon. At a temperature as high as 750 °C, an increase in the X-ray reflection intensity indicated the ordering of graphite-like crystallites. At high burn-off degrees, the size of coherently scattering domains becomes smaller, and an increased background in X-ray patterns indicates the destruction of cellulose nanofibrils, the disordering of graphene stacks, and an increase in the amount of disordered carbon. At this stage, pores develop in the crystallites. They are tentatively assigned to crystallites with sizes of 15–20 nm and to micropores. According to the Raman spectra combined with the XRD and SAXS data, the structure of all the pyrolysis products is influenced by the complex structure of the walnut shell precursor, which comprises cellulose nanofibrils embedded in lignin. This structure was preserved in the initial stage of pyrolysis, and the graphitization of cellulose fibrils and lignin proceeds at different rates. Most of the pores accessible for gas molecules in the resulting carbon materials are associated with former cellulose fibrils.

Orientational order parameter and mean square displacement of solid heavy nitrogen in the low-temperature phase. Experimental data

This work presents the results of the analysis of the temperature dependence of the x-ray reflection intensity from solid heavy nitrogen in the ordered phase. The temperature dependence of the behavior of the orientational order parameter and mean square displacement of 15N2 molecules obtained from x-ray data is plotted. Based on the dependencies obtained, the orientational order parameter was determined at 0 K, which is 12% higher than the orientational order parameter obtained in theoretical works. It was found that the heavy nitrogen molecule “freely” rotates in the crystal at temperatures above 45 K.

Contribution of Lattice Defects to the Intensity of Quasi-Forbidden X-ray Reflections of Diamond: Comparison of X-Ray Topography and Infrared Spectroscopy Data

New developments of application of X-ray topography in the quasi-forbidden (222) reflection from perfect crystals with diamond lattice to investigate defects are presented. The spatial distribution of intensities of (111) and (222) X-ray reflections is correlated with the distribution of point defects in synthetic diamonds of various types. It is shown that X-ray topography in the quasi-forbidden (222) reflection is a promising tool for investigation of weak stress fields in perfect crystals.

Solid phase reaction between components of the charge in the areas burning solid fuel and features of formation liquid phase

Objective. The influence of solid-phase reactions in the agglomerated charge layer on the quality of manganese ag-glomerate is considered. Research methodology. Thermodynamic analysis was used to establish the predominance of reactions. The phase (mineral) composition of manganese concentrates and the experimental agglomerate was investigated by X-ray diffraction method on a DRON-2 diffractometer in monochromatic Cuα radiation. The interplanar distances at the corresponding values of the X-ray reflection intensity from the investigated samples of concentrates and agglomerate were determined by comparing the obtained data with the corresponding tabular data given in the reference books on X-ray diffraction analysis of substances. Sintering of the experimental agglomerate was performed on a laboratory agglomeration bowl. Research results. It is established that the dissociation of higher manganese oxides begins at relatively low temperatures and proceeds in stages to the formation of MnO. Since the chemical affinity of manganese for oxygen is significant, reduction to metallic Mn was not observed, as this requires a high content of reducing agent and a reducing atmosphere, which is difficult to achieve in real agglomeration processes. Dissociation of rhodochrosite carbonate concentrate and gradual dissociation of dolomitized limestone leads to an increase in CO2 content in the atmosphere. Slag bonds are represented by compounds Mn2SiO4, MnO • Al2O3, Mg2SiO4, CaO • MgO • SiO2, 2CaO • SiO2. Thermodynamic calculations show that at moderate temperatures, compounds such as calcium ferrites are not formed, which is likely for the interaction between basic flux oxides and manganese oxides. Scientific novelty. Studies have shown that CaO does not completely convert to a slag bond, and even with a basicity of order 1, there is undigested lime. White spots are formed in the structure of the finished agglomerate. Such an agglomerate during transportation and storage loses strength and a large amount of trifles is formed..

In situ observation of atomic movement in a ferroelectric film under an external electric field and stress

Atomic movement under application of external stimuli (i.e., electric field or mechanical stress) in oxide materials has not been observed due to a lack of experimental methods but has been well known to determine the electric polarization. Here, we investigated atomic movement arising from the ferroelectric response of BiFeO3 thin films under the effect of an electric field and stress in real time using a combination of switching spectroscopy, time-resolved X-ray microdiffraction, and in situ stress engineering. Under an electric field applied to a BiFeO3 film, the hysteresis loop of the reflected X-ray intensity was found to result from the opposing directions of displaced atoms between the up and down polarization states. An additional shift of atoms arising from the linearly increased dielectric component of the polarization in BiFeO3 was confirmed through gradual reduction of the diffracted X-ray intensity. The electric-field-induced displacement of oxygen atoms was found to be larger than that of Fe atom for both ferroelectric switching and increase of the polarization. The effect of external stress on the BiFeO3 thin film, which was controlled by applying an electric field to the highly piezoelectric substrate, showed smaller atomic shifts than for the case of applying an electric field to the film, despite the similar tetragonality.

Quantitative Phase Analysis of Plasma-Treated High-Silica Materials

The paper presents the X-ray diffraction (XRD) analysis of the crystal structure of SiO2 in two modifications, namely quartzite and quartz sand before and after plasma treatment. Plasma treatment enables the raw material to melt and evaporate after which the material quenches and condenses to form nanoparticles. The Rietveld refinement method is used to identify the lattice parameters of SiO2 phases. It is found that after plasma treatment SiO2 oxides are in the amorphous state, which are modeled within the microcanonical ensemble. Experiments show that amorphous phases are stable, and model X-ray reflection intensities approximate the experimental XRD patterns with fine precision. Within the modeling, full information is obtained for SiO2 crystalline and amorphous phases, which includes atom arrangement, structural parameters, atomic population of silicon and oxygen atoms in lattice sites.

Radiation response of cubic mesoporous silicate and borosilicate thin films

Abstract The radiation response has been studied of cubic mesoporous silicate and borosilicate thin films having different boron contents prepared using the block copolymer template Brij 58 and the dip coating technique. The degree of pore ordering of the films was analysed using low-angle X-ray diffraction and film thickness measured by X-ray reflectivity. For films calcined at 350 °C, the incorporation of boron resulted in a reproducible oscillatory variation in the d-spacing and intensity of the primary reflection as a function of boron content. A clear peak was observed in the d-spacing at 5–10 mol% boron incorporation. For borosilicate films of a given composition an overall suppression of d-spacing was observed as a function of aging time relative to films that did not contain boron. This was ascribed to a slow condensation process. The films were irradiated in pile with neutrons and with iodine ions at energies of 180 keV and 70 MeV. Neutron irradiation of the silicate thin films for periods up to 30 days and aged for 400 days resulted in little reduction in either d-spacing or intensity of the primary low-angle X-ray reflection indicating that the films retained their mesopore ordering. In contrast borosilicate films for which the B (n, α) reaction was expected to result in enhanced displacement damage showed much larger variations in X-ray parameters. For these films short irradiation times resulted in a reduction of the d-spacing and intensity of the primary reflections considerably beyond that observed through aging. It is concluded that prolonged neutron irradiation and internal α irradiation have only a small, although measurable, impact on mesoporous borosilicate thin films increasing the degree of condensation and increasing unit cell contraction. When these borosilicate films were irradiated with iodine ions, more profound changes occurred. The pore ordering of the films was significantly degraded when low energy ions were used. In some cases the degree of damage was such that no low-angle reflection could be observed. This degradation of pore ordering was confirmed in scanning electron microscopy images of the irradiated films.

Static magnetic proximity effect inPt/Ni1−xFexbilayers investigated by x-ray resonant magnetic reflectivity

We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive tool to detect proximity induced interface spin polarization in Pt/Fe, Pt/Ni$_{33}$Fe$_{67}$, Pt/Ni$_{81}$Fe$_{19}$ (permalloy), and Pt/Ni bilayers. We demonstrate that a detailed analysis of the reflected x-ray intensity gives insight in the spatial distribution of the spin polarization of a non-magnetic metal across the interface to a ferromagnetic layer. The evaluation of the experimental results with simulations based on optical data from ab initio calculations provides the induced magnetic moment per Pt atom in the spin polarized volume adjacent to the ferromagnet. We find the largest spin polarization in Pt/Fe and a much smaller magnetic proximity effect in Pt/Ni. Additional XRMR experiments with varying photon energy are in good agreement with the theoretical predictions for the energy dependence of the magnetooptic parameters and allow identifying the optical dispersion $\delta$ and absorption $\beta$ across the Pt L3-absorption edge.

Crystal-forming functions of glide planes in the structural organization of a number of (Pb, Bi)-containing sulfides

The reasons for the preference of glide planes in natural crystals are considered by studying the results of an X-ray crystallography analysis of the minerals salzburgite, eldragonite, izoklakeite, and vikingite. The glide planes organize the combination of right- of atomic fragments, which appear during crystallization, and contribute to a uniform distribution of atoms in complex compositions and a more dense and symmetrical packing. The fact that the structures have cation and anion sublattices with similar dimensions and orientations creates a situation similar to that of beats in oscillatory systems and, hence, modulates the intensity of X-ray reflections. The progressively increasing number of structures where individual atomic positions are occupied by two or more types of atoms suggests a stable geometry of the corresponding atomic sublattices with respect to compositional variations. Analysis of these “skeletal” sublattices is a key to understanding the solid-phase transformations, contact interactions, and dynamic processes in mineral associations.

Complex oxide growth using simultaneous in situ reflection high-energy electron diffraction and x-ray reflectivity: When is one layer complete?

During layer-by-layer homoepitaxial growth, both the Reflection High-Energy Electron Diffraction (RHEED) intensity and the x-ray reflection intensity will oscillate, and each complete oscillation indicates the addition of one monolayer of material. However, it is well documented, but not well understood, that the phase of the RHEED oscillations varies from growth to growth and thus the maxima in the RHEED intensity oscillations do not necessarily occur at the completion of a layer. We demonstrate this by using simultaneous in situ x-ray reflectivity and RHEED to characterize layer-by-layer growth of SrTiO3. We show that we can control the RHEED oscillation phase by changing the pre-growth substrate annealing conditions, changing the RHEED oscillation phase by as much as 137°. In addition, during growth via pulsed laser deposition, the relaxation times between each laser pulse can be used to determine when a layer is complete, independent of the phase of the RHEED oscillation.

Structure and composition of silicon carbide films synthesized by ion implantation

The mathematical decomposition of the IR absorption spectrum obtained from a Si layer after the C+ ion implantation with an energy of 10 or 40 keV or from a homogeneous SiC0.7 film has demonstrated that fractions of weak elongated Si-C bonds in the amorphous phase, strong shortened Si-C bonds on the surface of small nanocrystals, and tetrahedral Si-C bonds in the crystalline phase (degree of crystallinity) after high-temperature annealing (1250–1400°C) of the layers are equal to 29/29/42, 22/7/71, and 21/31/48%, respectively. A system of SiC2.0, SiO2, SiC0.8, and SiC0.6 layers in the film on the Si substrate has been identified using X-ray reflectometry and the simulation with the Release software. The reflectometry data on fluctuations of the intensity of X-ray reflections in the region of the main maximum have been interpreted in terms of variations in the density over the depth of the layer with a Gaussian distribution of carbon atoms from 2.55 and 2.90 g/cm3 for the SiC0.25 and SiC0.65 layers, respectively, to 3.29 g/cm3 for the SiC1.36 layer.

Metalorganic vapor phase epitaxy growth of ternary tetradymite Bi2Te3−xSex compounds

We report on a metal organic vapor epitaxy (MOVPE) of Bi2Te3−xSex films over the entire range of compositions (0≤x≤3) for the first time. The films were grown on Al2O3(0001) substrates at 465°C using trimethylbismuth (Bi2Me3), diethyltellurium (Et2Te) and diisopropylselenium (iPro2Se) as metalorganic sources. To realize the 2D growth mode and to grow films with flat surfaces and high crystalline quality, a thin ZnTe buffer layer was used. As-grown films were studied using optical and AFM microscopy techniques and X-ray diffraction. It was found that under steady growth conditions the composition of Bi2Te3−xSex films strongly depends on the film thickness. But a high rate of interdiffusion of chalcogens at the growth temperature rapidly leads to a homogeneous composition of the film in the growth direction. Dependence of the intensity of X-ray reflection (0012) on the composition of Bi2Te3−xSex films x has extremes near x=1 (Bi2Te2Se) and x=2 (Bi2Se2Te). The AFM micrographs and profiles show large (above 2μm) triangle-shaped atomically flat terraces with step height of a quintuple layer (0.90nm) of the tetradymite-type compounds. The electronic properties of the grown films have been characterized via four probe magnetotransport measurements.

Ulrich Wolfgang Arndt. 23 April 1924 — 24 March 2006

Ulrich (Uli) Arndt was a physicist and engineer whose contributions to the development of a wide range of instrumentation for X-ray crystallography played an important part in our ability to solve the atomic structure of large biological molecules. Such detailed information about protein structures has for the past 50 years underpinned the huge advances in the field of molecular biology. His innovations spanned all aspects of data generation and collection, from improvements in X-ray tubes, through novel designs for diffractometers and cameras to film scanners and more direct methods of X-ray detection. When he started in the field, the intensities of individual X-ray reflections were often estimated by eye from films. By the end of his career the whole process of collecting from a crystal a three-dimensional data set, possibly comprising hundreds of thousands of measurements, was fully automated and very rapid.

地球化学標準物質（堆積物シリーズ）に逐次溶解法を適用した際に生じる鉱物組成変動

We have applied the sequential extraction procedure developed by the Community Bureau of Reference (BCR) to eight Japanese geochemical reference materials. By using this method, we attempt to extract exchangeable and carbonate phases in step 1, extract iron hydroxide and manganese oxide in step 2, and extract metal sulfide and organic material in step 3. We use X-ray diffractometry (XRD) to measure untreated samples and the residue of samples after each step of the extraction process to determine whether the target material is satisfactorily decomposed during the procedure. For JSd-1 and JSd-3, XRD patterns do not change significantly by using the BCR procedure. Actually, most of the elements in these materials are scarcely extracted by BCR scheme. The peaks of calcite in JSd-4, JMs-1 and JMs2 disappear in the XRD patterns after the first extraction procedure. The result suggests that the target phase of step 1 process is fully decomposed. JLk-1 and JMs-2 show high concentrations of the Fe and Mn extracted in step 2. However, it is difficult to clearly confirm the full decomposition of iron hydroxide and manganese oxide in step 2 because these materials do not show distinct peaks in the XRD patterns. Pyrite in JMs-1 disappears in step 3 of the extraction, which suggests that sulfide is satisfactorily decomposed in this process. X-ray reflection intensities of some peaks for quartz and plagioclase in JSO-1 increase significantly after step 3 of the extraction. It is assumed that organic material thickly covered the mineral surfaces and reduced the X-ray reflection from the minerals prior to the third procedure. Although this evidence is indirect, we conclude that organic material is successfully decomposed and removed from the mineral surface during the third extraction procedure. On the basis of these results, it is confirmed that the BCR protocol can properly extract target materials from the geochemical reference materials.

Recrystallization of BCC Metals: Distribution of Strain Hardening and Texture Formation

Data are presented on the x-ray line broadening distribution over the texture of cold-rolled Nb and Mo sheets. The method of generalized X-ray pole figures, which combine texture measurements with X-ray line profile analysis, is employed. The X-ray line broadening is considered as an indicator of residual deformation effects. It was revealed that these effects in cold-rolled BCC metals rise as the grain orientation shifts away from texture maxima towards texture minima. The intensity of X-ray reflections change during annealing at 200 – 500C and this change correlates with the line broadening. The recrystallization texture of BCC metals is dominated by orientations deflected from the peak maxima by 25 – 30 deg. These orientations in the deformed structure have relatively high stored energy. Their volume fraction is sufficient for them to be able to consume most of the deformed matrix.

Banana-shaped molecular architecture: Formation of large columns composed of two concentrically enclosed layers

The room-temperature solid phase (X3) of banana-shaped molecules that forms on cooling from the B6 phase is characterized as having an extremely large hexagonal lattice. In this study, we acquired a detailed structure of the X3 phase from synchrotron radiation (SR) micro-beam X-ray and atomic force microscopy (AFM) measurements. Focusing the micro X-ray beam on a single fan-shaped domain, we observed a well-oriented pattern including nine hk0 reflections with spacings of 20–110 A. These can be indexed with a two-dimensional (2-D) hexagonal lattice with an edge length of 126.8 A and incorporating approximately 70 molecules. The hk0 reflections appear in a direction parallel to the long axis of the fan-shaped domain showing that the two-dimensional lattice exists in a plane perpendicular to both the layer and bent direction of the molecules in the preceding B6 phase. An AFM image clearly illustrates the close packing of cylinders with a diameter equal to the hexagonal lattice edge. Further, the electron density map elucidated from the X-ray reflection intensity distribution shows that each cylinder is constructed of two concentrically enclosed layers.

Thin films of a ferroelectric phenazine/chloranilic acid organic cocrystal

Phenazine–chloranilic acid cocrystal thin films can be formed by vacuum evaporation of the component molecules onto cooled substrates. Fluxes of phenazine and chloranilic acid were provided from separate sublimation sources, from which the cocrystalline phase can be formed under a wide range of impingement rates of the component molecules. Substrates consisted of Au or Ni thin films on Si wafers, cooled to 100–140 K during deposition. X-ray diffraction and scanning electron microscopy show that this process yields polycrystalline thin films of the cocrystal with voids between crystalline grains. The relative intensities of X-ray reflections differ from reported intensities of polycrystalline powders, suggesting that the films have an anisotropic distribution of crystallographic orientations. The cocrystalline thin films have an effective dielectric constant of 13 at room temperature, increasing at lower temperatures and exhibiting a broad maximum near 200 K. The means to grow thin films of organic ferroelectric materials will allow the integration of new functionalities into organic electronic device structures, including capacitors and field-effect transistors.

Application of X-ray reflection interface microscopy to thin-film materials

Abstract New X-ray imaging techniques with excellent spatial resolution are under development for investigating surface and interface structures. X-ray reflection imaging microscopy (XRIM) applies full-field imaging to a specularly reflected X-ray beam from a surface or interface. This technique uses a zone plate objective lens to spatially resolve the reflected X-ray intensity and, by exploiting phase contrast, allows steps or terraces to be directly visualized. Thickness fringes caused by interferences in crystalline thin films grown on single-crystal substrates are observed near Bragg peaks and also carry information related to the termination of the film at either the surface or the film–substrate interface. We have applied the XRIM technique to image X-ray intensity along thickness fringes in complex oxide thin-film systems such as SrRuO 3 on SrTiO 3 , EuTiO 3 on DyScO 3 , and Bi 2 O 3 on SrTiO 3 . Measurements of the contrast variations in the images as a function of momentum transfer, Q , allow features to be identified as steps/terraces, or attributed to film inhomogeneities. Using both the Q -resolution and the excellent spatial resolution of the XRIM technique, images of fabricated systems with lateral structures are demonstrated.

Ion channel forming self-assembling systems based on benzenesulfonic acid with unsaturated aliphatic substituents

The structure and phase behavior of amphiphilic compound sodium 2,3,4-tri(dodecyl)benzenesulfonate, which is capable of self-assembling and contains methacryloyl groups in aliphatic ends, were studied by X-ray diffraction and differential scanning calorimetry. The initial samples are characterized by an ordered columnar ϕ oh phase, which, during a rise in temperature to 53°C (at the expense of mobility, an increase in mesogenic groups, and a loss of order in their mutual arrangement), transforms into a disordered columnar ϕ h phase. Under the action of irradiation, the cross-linking of benzenesulfonate molecules by methacryloyl groups and the formation of a continuous polymer matrix occur, which leads to a consistency of the column diameter at high temperatures. Cross linking proceeds much more intensively in the area where the disordered columnar phase exists. To analyze the structure of the columnar phase, we used an established technique: the reconstruction of electron density distribution maps in cylindrically symmetric systems from the relation of the intensities of small-angle X-ray reflections. Mutual ordering of benzenesulfonic groups in the area where the ϕ oh phase exists leads to the formation of ordered ion channels; this opens up possibilities to use this material to make ion-selective membranes with controlled conductivity.

Method for estimating the morphological significance of simple forms of crystals from X-ray data

When developing V.I. Mikheev and I.I. Shafranovskiĭ’s method for estimating the morphological significance of faces of different simple forms from X-ray reflection intensities, a way to approximately evaluate the morphological significance of simple forms on crystals from the structure amplitudes of the corresponding atomic planes is proposed. The potential for this approach is demonstrated by the examples of marcasite and zircon.