Modern Synchrotron Radiation Sources Research Articles

Использование метода синхротронной компьютерной ламинографии при изучении особенностей строения металлических сплавов (обзор исследований)

The paper contains a review of research related to the use of synchrotron radiation computed laminography in the study of the structure features of metal alloys subjected to various methods of external action. Introduction. The important role of X-rays in the field of materials research is discussed. The capabilities of standard X-ray devices equipped with X-ray tubes and modern synchrotron radiation (SR) sources with unique parameters are compared. Methods for studying flat samples. Tomography and synchrotron laminography. An informative method based on the use of synchrotron X-rays is synchrotron radiation computed tomography (SRCT), which allows obtaining cross-section images of objects by processing multiple absorption radiographs. A brief classification of five generations of tomographs is presented. The problems encountered in obtaining data from non-compact (non-isometric) samples are avoided by using the method of synchrotron radiation computed laminography (SRCL), which combines the principles of laminography with the advantages of synchrotron imaging. Currently the method is used for non-destructive testing of non-isometric objects by a number of synchrotron radiation sources (ESRF, ANKA, Spring-8). Resolution of synchrotron radiation computed laminography. The use of monochromatic radiation in realization of computed laminography method is a factor, which provides high spatial resolution down to micron and submicron scale. An equally important factor is related to the characteristics of the detector. Images with a resolution of ~100 nm were obtained using nanolaminography. Comparison of laminography and tomography methods. Augmented laminography. Augmented laminography allows improving image quality by augmenting the Fourier space analyzed by laminography with information obtained from lower resolution CT. Reconstruction performed using Augmented laminography is characterized by the absence of significant artifacts and high resolution. Implementation of the laminography method. The angle of inclination of the rotary axis θ (SRCL method) is related to the geometry of samples and is determined experimentally in each case. In order to achieve the necessary resolution, the value θ should provide an optimal average value of the intensity of the passed radiation. The energy of X-rays is calculated on the basis of material characteristics. To reconstruct images of the objects, software complexes that implement the filtered back projection method based on the Radon transform are used. Examples of laminography application for analysis of metal alloys samples. The laminography method can be used for in-situ investigations allowing real time monitoring of processes occurring under different conditions of external action, e.g. during plastic deformation of metal plates. Data on formation of pore-type defects in the process of loading of metal workpieces are interesting. Numerous examples of post-mortem studies of metal alloys for various purposes are described in the literature. Important information is obtained in the study of fatigue cracks, as well as defects arising in the process of contact-fatigue loading of materials. Conclusion. The SRCT and SRCL methods are rationally implemented at the generation 4+ synchrotron radiation source “SKIF” under construction in Novosibirsk.

Exploring Structural Changes, Manufacturing, Joining, and Repair of Intermetallic γ‐TiAl‐Based Alloys: Recent Progress Enabled by In Situ Synchrotron X‐Ray Techniques

Intermetallic γ‐TiAl‐based alloys are a promising class of materials for lightweight high‐temperature applications. Following intensive research and development activities, they have recently entered service in the automotive and aircraft engine industries. In the course of the past decades, the development of these complex multiphase alloys has benefited considerably from the application of (in situ) X‐ray scattering and diffraction techniques. Herein, a practical introduction and overview of recent progress in this field of research are provided. In particular, four case studies taken from various stages in the alloy development (i.e., fundamental research—manufacturing, joining, and repair—and application) illustrate current prospects at modern synchrotron radiation sources, including detailed information on available setups for in situ high‐energy X‐ray diffraction and small‐angle X‐ray scattering experiments and a discussion of potential limitations in the use of these techniques.

Nuclear resonant scattering from 193Ir as a probe of the electronic and magnetic properties of iridates

The high brilliance of modern synchrotron radiation sources facilitates experiments with high-energy x-rays across a range of disciplines, including the study of the electronic and magnetic correlations using elastic and inelastic scattering techniques. Here we report on Nuclear Resonance Scattering at the 73 keV nuclear level in 193Ir. The transitions between the hyperfine split levels show an untypically high E2/M1 multi-polarity mixing ratio combined with an increased sensitivity to certain changes in the hyperfine field direction compared to non-mixing transitions. The method opens a new way for probing local magnetic and electronic properties of correlated materials containing iridium and provides novel insights into anisotropic magnetism in iridates. In particular, unexpected out-of-plane components of magnetic hyperfine fields and non-zero electric field gradients in Sr2IrO4 have been detected and attributed to the strong spin-orbit interaction in this iridate. Due to the high, 62% natural abundance of the 193Ir isotope, no isotopic enrichment of the samples is required, qualifying the method for a broad range of applications.

Large-aperture X-ray refractive lens

An X-ray refractive lens with an enlarged aperture (multilens) is developed and a procedure for obtaining images using this lens and methods of their processing are proposed. The multilens is compared with conventional X-ray refractive lenses, and the method of processing is compared to known techniques. It is shown that the proposed multilens can receive X-ray images with an aperture ratio of two to three orders of magnitude greater than a conventional X-ray refractive lens. Possible applications of the multilens are considered. Most attractive is use of the proposed multilens for imaging biological objects with a very low concentration of contrast agent. Quantitative estimates show that images of such objects can be obtained using modern synchrotron-radiation sources with a resolution of approximately 1 μm in hundreds of seconds.

Partially coherent X-ray wavefront propagation simulations including grazing-incidence focusing optics.

X-ray beamlines in modern synchrotron radiation sources make extensive use ofgrazing-incidence reflective optics, in particular Kirkpatrick-Baez elliptical mirror systems. These systems can focus the incoming X-rays down to nanometer-scale spot sizes while maintaining relatively large acceptance apertures and high flux in the focused radiation spots. In low-emittance storage rings and in free-electron lasers such systems are used with partially or even nearly fully coherent X-ray beams and often target diffraction-limited resolution. Therefore, their accurate simulation and modeling has to be performed within the framework of wave optics. Here the implementation and benchmarking of a wave-optics method for the simulation of grazing-incidence mirrors based on the local stationary-phase approximation or, in other words, the local propagation of the radiation electric field along geometrical rays, is described. The proposed method is CPU-efficient and fully compatible with the numerical methods of Fourier optics. It has been implemented in the Synchrotron Radiation Workshop (SRW) computer code and extensively tested against the geometrical ray-tracing code SHADOW. The test simulations have been performed for cases without and with diffraction at mirror apertures, including cases where the grazing-incidence mirrors can be hardly approximated by ideal lenses. Good agreement between the SRW and SHADOW simulation results is observed in the cases without diffraction. The differences between the simulation results obtained by the two codes in diffraction-dominated cases for illumination with fully or partially coherent radiation are analyzed and interpreted. The application of the new method for the simulation of wavefront propagation through a high-resolution X-ray microspectroscopy beamline at the National Synchrotron Light Source II (Brookhaven National Laboratory, USA) is demonstrated.

A comprehensive facility for EXAFS measurements at the INDUS-2 synchrotron source at RRCAT, Indore, India

The EXAFS technique, which deals with fine structure oscillations observed in the X-ray absorption spectrum of an element from 50 eV to ~700 eV above its absorption edge, gives precise information regarding the short range order and local structure around the particular atomic species in the material. With the advent of modern bright synchrotron radiation sources, EXAFS has emerged to be the most powerful local structure determination technique, which can be applied to any type of material viz. amorphous, polycrystalline, polymers, surfaces and solutions etc. Over the last few years a comprehensive facility for carrying out EXAFS measurements with synchrotron radiation over variety of samples has been developed at the 2.5 GeV, Synchrotron Radiation Source (INDUS-2) at RRCAT, Indore, India. The facility consists of two operational beamlines viz., the energy dispersive EXAFS beamline (BL-08) and the Energy Scanning EXAFS beamline (BL-09).

A wave-optical toolbox for multiple CRL transfocators

Modern synchrotron radiation sources are usually equipped with state-of-the-art focusing setups. In the last decade, modular arrays of compound refractive lenses, the so called transfocators, have emerged as adjustable focusing optics elements. Several arrays of more than one hundred lenses are distributed in the x-ray beam path to obtain optimal focusing; however, fully wave-optical simulations of such set-ups are still missing.We present a simple toolbox of distributed computer codes to numerically propagate an x-ray beam through a sequence of transfocators, illuminated by a point-source and a partially coherent extended source.

High-resolution resonant inelastic soft X-ray scattering applied to liquids

The brilliance of modern synchrotron radiation sources and capabilities of new instrumentation facilitate resonant inelastic soft X-ray scattering of liquids and molecular materials with high spectral quality. Especially, when the energy resolution approaches the natural line widths a detailed analysis provides information about local potential surfaces, dynamic coupling between nuclear and electronic degrees of freedom, and intermolecular interactions. After briefly commenting on various sample handling systems we review the recent high-resolution RIXS results on liquid acetone. The experimental RIXS spectra excited at the O K edge demonstrate that the CO stretching mode dominates the vibrational progressions, and that softer modes are little affected by the nuclear dynamics in the intermediate state. It is shown that intermolecular coupling can be neglected in this specific case, and it is predicted that such interaction significantly broadens spectral features in liquids with larger dipole–dipole interaction. Analysis of the data further shows that initial state thermal excitations at room temperature have a noticeable influence on the spectral features.

Vibrationally resolved resonant inelastic soft X-ray scattering spectra of free molecules

The brilliance of modern synchrotron radiation sources and capabilities of new instrumentation facilitate molecular resonant inelastic soft X-ray scattering with high spectral quality. Especially, energy resolution of vibrational fine structure allows for a detailed analysis, providing information about the dynamic coupling between nuclear and electronic degrees of freedom. After a brief historical account and a short qualitative comparison between the radiative and non-radiative decay channels we review the recent results for the oxygen molecule. Nuclear wavepacket dynamics in bound and unbound states is studied, and in the latter case spatial quantum beats are observed as the dissociation proceeds via two different electronic states. A new internal spin-coupling conservation rule is established, whereas a commonly accepted selection rule based on orbital symmetry is violated.

X-ray absorption near edge structure (XANES) study of some hydroxamic mixed ligand copper complexes

With the advent of modern bright synchrotron radiation sources, X-ray absorption spectra has emerged as a powerful technique for local structure determination, which can be applied to any type of material. The X-ray absorption measurements of four hydroxamic mixed ligand copper complexes have been performed at the recently developed BL-8 Dispersive EXAFS beamline at 2.5 GeV Indus-2 synchrotron at RRCAT, Indore, India. The X-ray absorption near edge structure (XANES) data obtained has been processed using data analysis program Athena. The energies of the K absorption edge, chemical shifts, edge-widths, shifts of the principal absorption maximum in the complexes have been determined. The values of the chemical shift suggest that copper is in oxidation state +2 in all of the complexes. The chemical shift data has been utilized to estimate effective nuclear charge on copper atom. The order of the chemical shifts has been correlated to the relative ionic character of the bonding in these complexes.

Molecular mechanism of actin-myosin motor in muscle

The interaction of actin and myosin powers striated and smooth muscles and some other types of cell motility. Due to its highly ordered structure, skeletal muscle is a very convenient object for studying the general mechanism of the actin-myosin molecular motor. The history of investigation of the actin-myosin motor is briefly described. Modern concepts and data obtained with different techniques including protein crystallography, electron microscopy, biochemistry, and protein engineering are reviewed. Particular attention is given to X-ray diffraction studies of intact muscles and single muscle fibers with permeabilized membrane as they give insight into structural changes that underlie force generation and work production by the motor. Time-resolved low-angle X-ray diffraction on contracting muscle fibers using modern synchrotron radiation sources is used to follow movement of myosin heads with unique time and spatial resolution under near physiological conditions.

Structure of Liquid Linear Alcohols

The properties of linear alcohols in the liquid phase are studied by molecular dynamics simulations. We analyze the effects of the use of bond length constraints on the simulation density, self-diffusion constant, and hydrogen-bonding characteristics of the alcohol series. We find that the densities are well-reproduced in each of the cases but that the constraints have clear effects on the value of the diffusion constant and hydrogen-bonding properties, which is probably caused by the use of a gas-phase reference value in the OH bond length constraint. Although finite size effects are found to be present in the hydrogen bond networks, the networks are determined to be composed of chain-type structures that are well-converged. The results indicate that liquid alcohols consist of hydrogen-bonded chains of molecules. This finding can likely be tested experimentally with inelastic X-ray techniques at modern synchrotron radiation sources.

Advances in synchrotron hard X-ray based imaging

Modern synchrotron radiation (SR) sources have dramatically fostered the use of SR-based X-ray imaging. The relevant information such as density, chemical composition, chemical states, structure, and crystallographic perfection is mapped in two, or, increasingly, in three dimensions. The development of nano-science requires pushing spatial resolution down towards the nanoscale. The present article describes a selection of hard X-ray imaging and microanalysis techniques that emerged over the last few years, by taking advantage of the flux and coherence of the SR beams, as well as exploiting the advances in X-ray optics and detectors, and the increased possibilities of computers (memory, speed). Examples are given to illustrate the opportunities associated with the use of these techniques, and a number of recent references are provided. To cite this article: J. Baruchel et al., C. R. Physique 9 (2008).

Izobretenie V.L. Ginzburgom ondulyatorov i ikh rol' v sovremennykh istochnikakh sinkhrotronnogo izlucheniya i lazerakh na svobodnykh elektronakh

Izobretenie V.L. Ginzburgom ondulyatorov i ikh rol' v sovremennykh istochnikakh sinkhrotronnogo izlucheniya i lazerakh na svobodnykh elektronakh

MAGNETISM AND LATTICE DYNAMICS OF NANOSCALE STRUCTURES STUDIED BY NUCLEAR RESONANT SCATTERING OF SYNCHROTRON RADIATION

Nuclear resonant scattering of synchrotron radiation is applied to investigate the magnetic structure and the lattice dynamics of nanoscale systems. The outstanding brilliance of modern synchrotron radiation sources allows for sensitivities to smallest amounts of material. Due to the isotopic sensitivity of the scattering process, ultrathin probe layers of Mössbauer isotopes can be used to map out the magnetic and vibrational structure of thin films with sub-nm spatial resolution. Elastic nuclear resonant scattering is applied to determine the magnetic spin structure of an exchange-coupled bilayer system. Inelastic nuclear resonant scattering was used to determine the vibrational density of states in Fe islands on the W(110) surface.

Combined X-ray and neutron fibre diffraction studies of biological and synthetic polymers

The fibrous state is a natural one for polymer molecules which tend to assume regular helical conformations rather than the globular structures characteristic of many proteins. Fibre diffraction therefore has broad application to the study of a wide range of biological and synthetic polymers. The purpose of this paper is to illustrate the general scope of the method and in particular to demonstrate the impact of a combined approach involving both X-ray and neutron diffraction methods.While the flux of modern X-ray synchrotron radiation sources allows high quality datasets to be recorded with good resolution within a very short space of time, neutron studies can provide unique information through the ability to locate hydrogen or deuterium atoms that are often difficult or impossible to locate using X-ray methods. Furthermore, neutron fibre diffraction methods can, through the ability to selectively label specific parts of a structure, be used to highlight novel aspects of polymer structure that can not be studied using X-rays.Two examples are given. The first describes X-ray and neutron diffraction studies of conformational transitions in DNA. The second describes structural studies of the synthetic high-performance polymer poly(p-phenylene terephthalamide) (PPTA), known commercially as Kevlar® or Twaron®.

Hard X-ray photoelectron spectroscopy: sensitivity to depth, chemistry and orbital character

Photoelectron spectroscopy is growing in importance as a tool for characterizing not only the surface but also the bulk of solids. Photon fluxes of modern synchrotron radiation sources compensate the cross-section lowering of photoelectrons with kinetic energy in the hard X-ray range, the only electrons able to escape from bulk regions. We present examples of photoelectron emission experiments where we measured core and valence photoelectrons up to ∼ 5 keV kinetic energy. We studied the evolution of photoelectron emission spectra collected at increasing incident photon energy: core-level spectra of Samarium and its compounds indicate increased bulk-sensitivity, valence band spectra reveal significant cross-section changes of electrons with different orbital character. The chemical and depth sensitivity given by the energy dependence of the attenuation length has been quantitatively assessed in the case of layered GaAs/AlAs/GaAs. These are examples of the wide scientific importance that hard X-ray photoelectron spectroscopy is acquiring in many aspects of the study of solids.

Resonant x-ray scattering as a probe of toroidal moments in centrosymmetric systems

The aim of this paper is to show that it is possible to detect, by means of resonant x-ray scattering (RXS), the magnetic toroidal moment and/or higher order time-reversal and parity-odd multipoles in centrosymmetric systems, where absorption-dichroic techniques are ineffective. We have found a material, ${\mathrm{Li}}_{2}\mathrm{V}\mathrm{O}\mathrm{Si}{\mathrm{O}}_{4}$, whose magnetic space group allows such a measurement. We then performed an ab initio numerical simulation based on a relativistic extension of the multiple scattering theory to show that the intensity of the RXS signal can be detected in modern third generation synchrotron radiation sources. Finally, we stress that RXS, unlike dichroism in absorption, allows a complete separation of toroidal dipole moment and higher order multipoles, due to the possibility of exploiting the extra degrees of freedom related to the incoming and outgoing polarizations.

Higher-order processes in X-ray photoionization and decay

Over the past decade, modern synchrotron radiation sources have provided continuously tunable, intense well-collimated beams of hard X-rays. Our group has exploited such beams, in the energy range 2–100 keV, to study higher-order processes in atomic photoionization and vacancy decay which were hitherto difficult to observe and we review five specific examples of that work here. These topics include high-energy photoionization of helium, nondipolar photoionization, double K-shell ionization, two-photon decays of inner-shell vacancies, and nuclear excitations by electronic transition.

Counting statistics of X-ray detectors at high counting rates.

Modern synchrotron radiation sources with insertion devices and focusing optics produce high fluxes of X-rays at the sample, which leads to a requirement for photon-counting detectors to operate at high counting rates. With high counting rates there can be significant non-linearity in the response of the detector to incident X-ray flux, where this non-linearity is caused by the overlap of the electronic pulses that are produced by each X-ray. A model that describes the overlap of detector pulses is developed in this paper. This model predicts that the correction to the counting rate for pulse overlap is the same as a conventional dead-time correction. The model is also used to calculate the statistical uncertainty of a measurement and predicts that the error associated with a measurement can be increased significantly over that predicted by Poisson (N(-1/2)) statistics. The error differs from that predicted by a conventional dead-time treatment.