Calculation of the parameters of the X-ray diffraction station with adaptive segmented optics on the side beam from the wiggler of the Sibir’-2 storage ring

The mounting of an X-ray diffraction station on the side beam of a 19-pole superconducting wiggler makes it possible not only to use the central synchrotron radiation beam with a wavelength of 0.5 ?, but also to solve problems requiring softer X rays at a synchrotron radiation (SR) intensity exceeding that for the beams from the bending magnet. A numerical simulation of the formation of photon beams from a source and their transmission through the elements of the station (and through the station as a whole) allows one to calculate the parameters of the station, compare it with the existing analogs, determine its potential and actual efficiency of its elements, and estimate the adjustment quality. A numerical simulation of the SR source on the side beam from the wiggler and the focusing channel (segmented condenser mirror, monochromator with sagittal focusing by the segmented second crystal, and segmented focusing mirror) has been performed. The sizes of the focus and the divergence of rays in it are determined with allowance for the finite sizes of segments. The intensity of radiation with a wavelength ?? = 1.0 ? in the focus is determined taking into account the loss in the SR extraction channel and in the focusing channel. The values of the critical wavelength for the side beam from the wiggler and the wavelength resolution are calculated. The intensities in the X-ray diffraction pattern and its angular resolution are found.     

Diffraction reflection of a focused X-ray wave by a multilayer crystal

The Bragg diffraction of a narrow X-ray beam in a multilayer crystal is studied in the reflection geometry. It is shown by computer simulation of the experiment that strong integrated kinematic reflection occurs at any boundary of a multilayer crystal at the point of intersection of a narrow beam with the boundary. In contrast to the dynamic diffraction of a plane wave, attenuation of a narrow incident beam due to the reflection is small in comparison with the conventional absorption. As an example of a multilayer crystal, a Fabry-Perot interferometer is considered, which consists of two 70-μm-thick crystal Si layers separated by a 100-μm-thick air layer. The 12 4 0 reflection is studied at a photon energy of 15 keV. Three methods of formation of a narrow beam are considered: wavefront limitation by a slit, focusing with a parabolic lens, and focusing with a zone plate. It is shown that, for a local analysis of the thickness of layers and scattering parameters, the method of parabolic lens focusing has some advantages in comparison with the other methods.     

Thermal strains in focusing channels of the stations for X-ray diffraction analysis in the Sibir-2 storage ring

The thermal load caused by the absorption of synchrotron radiation in X-ray optical elements of the Belok and RSA stations leads to optics elements heating and induces strains upon simultaneous cooling. The heating of the cooled first crystal in the double-crystal monochromator causes its bending and increases the reflected beam divergence, which, in turn, results in the monochromatic beam intensity loss [1]. Numerical simulation makes it possible to more accurately determine the strains, choose the optimal monochromator design, estimate the vertical sizes of the focal spot and wavelength resolution in the focusing channel, correctly design the system for cooling the mirror at the channel input, and choose a design providing the minimum temperature of the beam-limiting slit knives.     

On the update of DIN-2PI spectrometer

The prospects of increasing the resolution of the DIN-2PI spectrometer at initial neutron energies of 50–500 meV are discussed. The spectrometer resolution can be significantly improved using time-of-flight neutron monochromatization supplemented with a monochromator crystal. The application of this combined monochromatization technique makes the dependence that the instrumental resolution has on the duration of the neutron pulse from the IBR-2 reactor insignificant. This update will make it possible to perform experiments with initial neutron energies to several hundreds of meV in the energy-dumping mode, which, in turn, allows one to study condensed media in a wide range of temperatures, including cryogenic.     

Theoretical analysis of the possibilities of Zernike phase contrast method in hard X rays for nondestructive imaging of micropipes in a silicon carbide single crystal

The possibilities of using Zernike phase contrast in hard X rays for imaging micropipes in a silicon carbide single crystal are analyzed by numerical simulation. Calculations are performed for the experimental conditions characteristic of third-generation synchrotron radiation sources. A scheme is considered where the focusing element is a parabolic refracting lens and the phase-shifting element is mounted at the point of the source image. It is shown that micropipe cross sections by a beam with a longitudinal diameter reaching 10 μm are imaged by the lens without distortions. At the same time, the lens makes it possible to magnify the image several tens of times. The cross sections that are significantly elongated along the beam are imaged with artifacts; however, their structure can also be recovered. It is shown that polychromaticity of radiation does not significantly affect the object imaging.     

Laterally‐Graded SiGe Crystals for High Resolution Synchrotron Optics

A novel type of optical element for synchrotron radiation applications in the X‐ray region: namely laterally‐graded aperiodic crystals on the basis of Si_1‐xGe_x mixed crystal is presented. The lattice parameter of such gradient crystals containing up to some at. % Ge changes nearly linearly along the plane of diffraction. Thus the variation of the Bragg angle of divergent incident light on the crystal can be compensated. This opens up the possibility to operate a crystal monochromator in nearly crystal limited resolution in the whole energy range above 2 keV at the full vertical synchrotron source divergence without a collimating pre‐mirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si‐crystal monochromator.     

Fabrication of a new gradient-index rod lens with high performance

A gradient-index rod lens was fabricated by the new ion-exchange technique, in which another dopant was added to the fused salt. It was found that this dopant remained only in the merginal region of the glass rod and modified the improper refractive index distribution in this region. The lens has high numerical aperture of 0.6 and gives good results in the light focusing system and the light source coupling system.     

Texturtopographie

Using the X-ray beam coming from a Johannsson monochromator the represented method records the diffracted intensity not at the place of focusing according to Guinier technique but in the double distance from the specimen. If the analysed object is e.g. a polycristalline metal sample with inhomogenious texture one can obtain a texture topograph with a relationship between reflectivity of the reflection spot and the blackening of the equivalent spot on the film. A necessary requirement is a soller slit placed between sample and film to eliminate other than the focused rays of the diffraction are.     

The Microcamera Used for Photoelectron Excited by the X-ray Standing Wave (XSW) Recording and Submicron Layer Structure Studies

Information obtained owing to aquaintance with the course of the angular dependence of photoelectron intensity excited by the X-ray standing waves allows to determine, more explicitly, the state of crystal surface layer deformation. The aim of this work is to present a new measuring device constructed at the Institute of Physics of the Polish Academy of Sciences, especially the X-ray microcamera being simultaneously the proportional flowing counter used for measuring of photoelectron current emitted from the examined crystal. The angular dependence of the photoelectron current can be measured in coincidence with the angular running of rocking-curves. It is possible due to a computer program controlling the X-ray doble-crystal spectrometer, the microcamera and the electronic system for registration of the intensity of the diffracted beam as well the flowing counter. The scheme of the X-ray double-crystal spectrometer, the microcamera, and the electronic measuring system operation is given. There are also given the results of the introductory measurements carried out for the Si(111) implanted with the Au ions. The calculation of rocking-curve for non-disturbed crystal in the case of asymmetrically cut monochromator crystal was made. There was also estimated the range of depth from that the photoelectrons were emitted.     

The belok station for protein crystallography on the synchrotron radiation beam from the bending magnet in the Sibir-2 storage ring

Design modifications made in the initial project of the Belok station in the Sibir-2 storage ring and the alignment and calibration methods are considered. The main operating parameters of the station are reported. Protein single crystals in a capillary at T = 293 K and without a capillary at T = 95 K, powders (angular resolution Δ2? = 0.04°), and nanocrystalline Na and Cl₂ precipitates (sizes, shape, and orientation) in electron-irradiated NaCl crystals have been investigated. The problem of focusing of a short-wavelength synchrotron radiation beam with sagittal bending of the second crystal in the double-crystal monochromator at a limited source-to-sample distance is solved in the Belok project.     

Study of a macrodefect in a silicon carbid single crystal by means of X-ray phase contrast

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.     

Crystal monochromator with a large curvature of the sagittal bending

A new crystal monochromator is designed and tested. The crystal monochromator allows for the use of a large curvature of the sagittal bending and makes it possible to focus synchrotron radiation at a short wavelength and a limited distance from the synchrotron radiation source to the sample.     

Growth and characterization of 4‐Aminopyridinium‐4‐nitro phenolate single crystals

Organic optical material 4‐Aminopyridinium‐4‐nitro phenolate (4AP4NP) has been synthesized, and single crystals of size 20 x 14 x 6 mm³ have been grown from acetone solvent at room temperature by solvent evaporation technique. The grown crystals have been characterized by X‐ray diffraction to determine the cell parameters, and by FT‐IR technique to confirm the formation of the expected compound. The crystal belongs to monoclinic crystal system with space group P2₁/a.The structural perfection of the grown crystals has been analyzed by high‐resolution X‐ray diffraction (HRXRD) rocking curve measurements. The thermal stability of the compound has been determined by TG‐DTA curves. The transmittance of 4AP4NP has been used to determine the refractive index n; the extinction coefficient K and both the real ε_r and imaginary ε_i components of the dielectric constant as functions of photon energy. The optical band gap of 4AP4NP is 2.4 eV. The dielectric and mechanical behavior of the specimen was also studied. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A method for implementing the diffraction of a widely divergent X-ray beam

A method for implementing the diffraction of a widely divergent characteristic X-ray beam from a standard X-ray tube with a linear focal spot was improved. X rays, passing through a diaphragm 30 μm in diameter, diffract from a crystal adjacent to the diaphragm. The crystal, together with a photographic plate, rotates around the axis perpendicular to the plate. It is shown that the diffraction image is a set of hyperbolas in this case. The equations of the hyperbolas are obtained and investigated. A method for interpreting the diffraction images in the case of small crystal asymmetry is proposed.     

Beam focusing on stations with a Sibir’-2 synchrotron source for single-crystal studies of atomic structures

A scheme for obtaining a stationary monochromatic beam that can be focused in the horizontal and the vertical planes and rapidly tuned to a desirable wavelength with the aid of a bending magnet on a Sibir’-2 synchrotron source has been designed. The channel parameters and the size and profile of a sagittally bent single crystal of the double-crystal monochromator were chosen with the use of numerical simulation.     

A curved-crystal spectrometer for soft X-ray emission studies of metals and metallic alloys

Quantitative comparisons between obtained X-ray emission spectra of 3d-transition metal elements and their alloys as well as band structure calculations demand an energetic resolution of the order of E ≈ 1 eV. A highly resolving focussing X-ray spectrometer is described which allows very high quality X-ray emission spectra to be obtained. The spectrometer utilizes a spherically bent Si(111)-crystal operated on the Rowland circle. The selection, fabrication and testing of the crystal are described. A comparison between own measurements of line-width of Co-Kα_1,2- and Cu-Kα_1,2-emission lines as well as literature values is given. The required energetic resolution can be obtained in the upper range of the Bragg angle δ with the described X-ray spectrometer and a spherically bent crystal.     

The 0.96(Bi0.5Na0.5)TiO3 – 0.04BaTiO3 crystal structure: A high‐Q,high‐counting statistics synchrotron diffraction analysis

A synchrotron powder diffraction experiment, especially designed to shed light on the controversial problem of the crystal structure of 0.96(Bi_0.5Na_0.5)TiO₃ – 0.04BaTiO₃, is reported. The investigated material is a key component of the current international search for lead‐free ferro‐piezoelectrics. A wide angular range diffraction pattern was measured in high resolution configuration, with emphasis on trustable counting stastistics in the high‐Q interval. Cc and R3c structural models were tried as primary phases. The obtained experimental results are incompatible with the monoclinic model and clearly favor the rhombohedral symmetry.     

Growth of highly doped p-type ZnTe layers on GaAs using a nitrogen DC plasma cell

In this paper we report about the use of a DC plasma cell for nitrogen doping of ZnTe layers grown on GaAs substrates by molecular beam epitaxy (MBE). The samples, characterized by high resolution X-ray diffraction, photoluminescence and Hall measurements, show good crystalline quality and carrier concentrations as high as 1×10²⁰ cm^-3 with mobilities up to 30 cm²/V·s at room temperature. To our knowledge, this is the highest hole doping level reported so far in the literature for any wide-gap II–VI compound. The achieved hole concentration is one order of magnitude larger than values reported using an RF plasma source.     

Characterization of a newly synthesized organic nonlinear optical crystal: Urea ninhydrin monohydrate

Urea ninhydrin monohydrate (UNM) was synthesized and grown for the first time from aqueous solution employing the slow evaporation method. Single crystal structure was determined by X-ray diffraction data and it reveals that the crystal belongs to centrosymmetric with space group of P2₁/c. The grown crystals were characterized by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and UV–vis–NIR spectroscopy. Preliminary Z-scan measurement indicates that nonlinear refractive index of this crystal is −4.1×10⁻⁸ cm²/W. The etching study was performed to assess the growth pattern of the crystal. Dielectric response of the crystal was analyzed for different frequencies and temperatures.     

Transmission Electron Microscopical Studies of the Layered Structure of the Ternary Semiconductor CuIn5Se8

The structure of the off‐stoichiometric In‐rich ternary phase CuIn₅Se₈ was studied by means of electron diffraction and high‐resolution electron microscopy. The compound shows a layered structure with a 7‐layer stacking sequence of closed‐packed planes, which contains both cubic and hexagonal stacking of Se atoms. The studied CuIn₅Se₈ bulk crystal is known as the β‐phase of this compound.