Diffraction Signal Research Articles

In Situ Investigations of Elastic Strain State in Deep Rolled 4140H Steel by Neutron Diffraction Method

Abstract A deep rolling process was applied on 4140H steel specimens with a self-built loading frame and investigated in situ with neutron radiation using the SALSA instrument at the Institut Laue-Langevin (ILL). A neutron diffraction stress imaging approach was developed and used to determine material changes from the surface up to several millimeters inside the material by single expositions. The strains could be evaluated as deviations of the diffraction signal along the height of an area detector, and the theoretical maximum depth resolution was given by geometrical magnification together with the detector pixel size. The results of these experiments together with complementary post-process investigations could be used to link the internal load during the process with resulting material modifications such as the generated residual strains.

Probing chemical heterogeneity of Li-ion batteries by in operando high energy X-ray diffraction radiography

Uniformity of the crystal structure of battery electrodes inside a commercial prismatic Li-ion battery (LiCoO2|C) with a nominal capacity of 1200 mAh were examined by diffraction of a monochromatic photon beam (60 keV). Selected structural parameters related to lithium concentrations in the positive and negative electrodes were determined averaging over cell thickness on a 1 × 1 mm2 grid, thus resembling an experimental radiography technique with a pixel size of 1 mm2, where the diffraction signal is used instead of attenuation of the photon beam. Non-uniformities in a prismatic Li-ion battery were unambiguously revealed by remarkable differences of the diffraction signals and systematic deviations of structural properties at different scan positions. Observed lithium heterogeneities at nominal state-of-charge (SOC) = 100% state are attributed to SOC deviations caused by the current distribution inside the examined prismatic cell.

Multiscale wavelet decomposition of time-resolved X-ray diffraction signals in cyclohexadiene

We demonstrate how the wavelet transform, which is a powerful tool for compression, filtering, and scaling analysis of signals, may be used to separate large- and short-scale electron density features in X-ray diffraction patterns. Wavelets can isolate the electron density associated with delocalized bonds from the much stronger background of highly localized core electrons. The wavelet-processed signals clearly reveal the bond formation and breaking in the early steps of the photoinduced pericyclic ring opening reaction of 1,3-cyclohexadiene, which are not resolved in the bare signal.

Nanoporous-template-modulated azopolymers for enhancing reversible photo-transformation

Recyclable utilization of light energy is essential for current information processing. Photochromic films including azopolymers play a key role in capturing photons, in which many optical manipulations can be achieved. Commonly, inorganic nanoparticles are incorporated into organic azopolymers to increase photo-excitation efficiency and reduce the volume shrinkage rate. However, the aggregation of azopolymers and the uneven distribution of nanoparticles can affect both the material transparency and chemical activity. Reversibility of photo-transformation for such a photochromic system is thus inhibited. Here, a new method is proposed that titania porous films with high optical transparency are used as a nano-template for azopolymer deposition. The results showed that inorganic nanoporous structures not only enhance dye adsorption but also inhibit azopolymer aggregation. In a holographic recording, the diffractive signal is increased 3.6 fold and kept constant for a long time with the support of the TiO2 framework. Based on the property, erasable hologram reconstruction is obtained in the nano-hybrid film by the alternated excitation of coherent lights and single light from a blue laser. This work shows a bright way to inhibit molecule aggregation in solid matrices and contributes to exploit updatable photo-transformation devices.

Characterisation of complex fluid media by an angle-scanning ultrasound diffractometer

The characterisation of complex fluid media (particles in liquids) by ultrasound can provide information on the particle size distribution, concentration, and aggregation of the particles. In the Rayleigh scattering regime, systems of liquid particles are dominated by monopole scatter (potentially producing thermal waves), whereas solid particle suspensions are dominated by dipole scatter (producing shear waves); thus the angular dependence of the diffracted field is expected to be different in these cases. Since mode conversion mechanisms are affected by the proximity of particles and thus by the degree of aggregation, the effect of particle type and degree of aggregation is expected to be observed in the angle-dependent signals. We report an experimental investigation of the angle- and frequency-dependent diffracted signal from cylindrical samples (in tubing) of emulsions and suspensions. The experimental results are compared with theoretical predictions using effective homogeneous properties for the complex fluids derived from multiple scattering models. We identify the differences in the diffracted signals for complex media in which the scattering mechanisms are monopole or dipole-dominated.

Numerical study of Bragg CDI on thick polycrystalline specimens.

Bragg coherent diffraction imaging (BCDI) is a powerful X-ray imaging technique for crystalline materials, providing high resolution maps of structure and strain. The technique is typically used to study a small isolated object, and is in general not compatible with a bulk polycrystalline sample, due to overlap of diffraction signals from various crystalline elements. In this paper, we present an imaging method for bulk samples, based on the use of a coherent source. The diffracted X-ray beam from a grain or domain of choice is magnified by an objective before being monitored by a 2D detector in the far field. The reconstruction principle is similar to the case of BCDI, while taking the magnification and pupil function into account. The concept is demonstrated using numerical simulations and reconstructions. We find that by using an object-lens distance shorter than the focal length, the numerical aperture is larger than in a traditional imaging geometry, and at the same time the setup is insensitive to small phase errors by lens imperfections. According to our simulations, we expect to be able to achieve a spatial resolution smaller than 20 nm when using the objective lens in this configuration.

In situ serial crystallography for rapid de novo membrane protein structure determination

De novo membrane protein structure determination is often limited by the availability of large crystals and the difficulties in obtaining accurate diffraction data for experimental phasing. Here we present a method that combines in situ serial crystallography with de novo phasing for fast, efficient membrane protein structure determination. The method enables systematic diffraction screening and rapid data collection from hundreds of microcrystals in in meso crystallization wells without the need for direct crystal harvesting. The requisite data quality for experimental phasing is achieved by accumulating diffraction signals from isomorphous crystals identified post-data collection. The method works in all experimental phasing scenarios and is particularly attractive with fragile, weakly diffracting microcrystals. The automated serial data collection approach can be readily adopted at most microfocus macromolecular crystallography beamlines.

Fractal analysis of X-ray diffraction patterns of zirconia–alumina mixed oxides

X-ray diffractograms of amorphous material commonly exhibit complex shapes with broad background noise. The X-ray diffraction signal of amorphous material possesses order only at the firsts neighbors (i.e., at the sub-nanometric level). Extracting patterns from such complex signal can provide valuable information on the crystalline structure of amorphous material. In this regard, the aim of this study was explore the use of fractal analysis for extracting structural features of amorphous material from X-ray diffraction signals containing strong background fluctuations To this end, well-characterized mixtures of ZrO2-Al2O3 were prepared by the sol–gel method and calcined at the relative low temperature of 500 °C during 5 h. The fractal analysis carried out with detrended fluctuation analysis for samples with different ZrO2/Al2O3 relative content suggested the presence of long-term correlations. This means that the background noise is not random, containing patterns related to the incipient crystallinity of the mixed oxides. The analysis was complemented with Rietveld refinement using monoclinic and tetragonal symmetries of ZrO2. Despite pure ZrO2 synthesized in the same conditions as those compounds of the mixture ZrO2-Al2O3 is mostly monoclinic, consistent results were found when modeling specimens of the mixture as ZrO2-Al2O3 being tetragonal. Thus, adding Al2O3 has a similar effect in retarding the formation of monoclinic ZrO2 in the mixture compounds. Overall, the results showed that fractal analysis can be a useful tool for extracting valuable information on the structure of semi-crystalline materials from X-ray diffraction signals.

Comparison of residual stress before and after shot peening on the surface of a Ti-6Al-4V titanium alloy by μ-X360n equipment

This comparison study is on the residual stress of a Ti-6Al-4V titanium alloy before and after shot peening. The Ti-6Al-4V titanium alloy is one of the most widely used materials due to a very good comprehensive performance. Testing the titanium alloy reveals that it adopts a Cu Κα for the target material because it has a strong diffraction peak under the crystal surface (213). The equipment used is the two-dimensional surface diffraction method to test the stress of the Ti-6Al-4V titanium alloy. The two-dimensional surface agent contains a detector and the detector consists of a complete probe. The core component of the detector is greater than 2 inches in diameter and the size of the detector determinesits ability to collect the diffraction signal; the greater the acquisition ability, the stronger it is. This piece of equipment is currently the most advanced full two-dimensional piece of equipment. The residual stress in the x-direction on the upper surface of the Ti-6Al-4V titanium alloy before shot peening is 296 Mpa and the error is 12 Mpa. The residual stress in the y-direction was 106 MPa and the error was 16 Mpa. The residual stress on the surface x-direction of the Ti-6Al-4V titanium alloy after shot peening was −532 Mpa and the error was 27 Mpa. The residual stress in the y-direction was −87 Mpa and the error was 32 Mpa. The measurement results indicate that the stress orientation is not uniform and that there was an obvious texture. On the surface of the Ti-6Al-4V titanium alloy, the residual stress in the x-direction of the upper surface is −532 Mpa, which is consistent with the theory and principle. The two-dimensional detector needs only one exposure to get the complete material Debye ringaccording to the integrity of the Debye ring and its intensity distribution characteristics. It can be concluded that the Ti-6Al-4V titanium alloy has a texture after shot peening. The stress change principle of the Ti-6Al-4V titanium alloy was compared from tensile stress to compressive stress, before and after the shot peening treatment.

Modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering

We report the modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering from x-ray diffraction experiments and magnetic measurements. The incommensurate modulation was observed on (n n 3m+3/2) type diffraction signal around magnetic ordering temperature where n and m are integer. The modulation was also observed on charge ordering signal, indicating spin-charge coupling. The incommensurate modulation was observed only on (n/3 n/3 3m) type charge ordering signal. This selectivity can be explained by polar charge ordering models.

Validation of Registration Techniques Applied to XRD Signals for Stress Evaluations in Titanium Alloys

To estimate stresses near specimen surfaces, X-ray diffraction (XRD) is applied to titanium alloys. Some of these alloys are difficult to study since they are composed of various phases of different proportions, shapes and scales. For millimetric probed volumes, such multi-phase microstructures induce shallow and noisy diffraction signals. Two peak registration techniques are introduced and validated thanks to tensile tests performed on two titanium alloy samples.

The role of MOFs in Thin-Film Nanocomposite (TFN) membranes

Incorporation of MOFs in interfacially polymerized Thin-Film Nanocomposite (TFN) membranes has widely been shown to result in increased membrane performance. However, the exact functioning of these membranes is poorly understood as large variability in permeance increase, filler incorporation and rejection changes can be observed in literature. The synthesis and functioning of TFN membranes (herein exemplified by ZIF-8 filled polyamide (PA) membranes prepared via the EFP method) was investigated via targeted membrane synthesis and thorough characterization via STEM-EDX, XRD and PALS. It is hypothesized that the acid generated during the interfacial polymerization (IP) at least partially degrades the crystalline, acid-sensitive ZIF-8 and that this influences the membrane formation (through so-called secondary effects, i.e. not strictly linked to the pore morphology of the MOF). Nanoscale HAADF-STEM imaging and STEM-EDX Zn-mapping revealed no ZIF-8 particles but rather the presence of randomly shaped regions with elevated Zn-content. Also XRD failed to show the presence of crystalline areas in the composite PA films. As the addition of the acid-quenching TEA led to an increase in the diffraction signal observed in XRD, the role of the acid was confirmed. The separate addition of dissolved Zn2+ to the synthesis of regular TFC membranes showed an increase in permeance while losing some salt retention, similar to observations regularly made for TFN membranes. While the addition of a porous material to a TFC membrane is a straightforward concept, all obtained results indicate that the synthesis and performance of such composite membranes is often more complex than commonly accepted.

Unexpected Composition Dependence of the First Sharp Diffraction Peak in an Alcohol–Aldehyde Liquid Mixture: n‐Pentanol and Pentanal

The total scattering structure factors of pure liquid n‐pentanol, pentanal, and five of their mixtures, as determined by high energy synchrotron X‐ray diffraction experiments, are presented. For the interpretation of measured data, molecular dynamics computer simulations are performed, utilizing “all‐atom” type force fields. The diffraction signals in general resemble each other over most of the monitored scattering variable, Q, range above 1 Å−1, but the absolute values of the intensities of the small‐angle scattering maximum (“pre‐peak,” “first sharp diffraction peak”), around 0.6 Å−1, change in an unexpected fashion, non‐linearly with the composition. Molecular dynamics simulations are not able to reproduce this low‐Q behavior; on the other hand, they do reproduce the experimental diffraction data above 1 Å−1 rather accurately. Partial radial distribution functions are calculated based on the atomic coordinates in the simulated configurations. Inspection of the various OO and OH partial radial distribution functions clearly shows that both the alcoholic and the aldehydic oxygens form hydrogen bonds with the hydrogen atoms of the alcoholic OH‐group.

Interpretation of Indications Generated by Small Welding Discontinuities in Ultrasonic Time of Flight Diffraction Technique

The article presents results of research on non-destructive ultrasonic time of flight diffraction technique TOFD and metallographic examinations of selected cross-sections of a MAG welded joint. The main objective was to compare the results of TOFD and metallographic examination at the locations where a large number of point-like indications, located on specific depths, have been detected on TOFD images and analyse the impact of this type of indication on results of a welded joint evaluation. Considered, that the indications have not exhibited separations between upper and lower diffraction signals, because of their small heights, measuring of height of indications in those cases was impossible. In all cases, the occurrence of discontinuities of 0.16–0.78 mm in height, in locations indicated by TOFD has been confirmed.

X-ray diffraction imaging of cardiac cells and tissue

With the development of advanced focusing optics for x-rays, we can now use x-ray beams with spot sizes in the micro- or nanometer range to scan cells and large areas of tissues and continuously record the diffraction signals. From this data, x-ray scattering maps or so-called x-ray darkfield images are computed showing how different types of cells or regions of tissues differ in their diffraction intensity. At the same time a diffraction pattern is available for each scan point which encodes the local nanostructure, averaged over many contributing constituents illuminated by the beam. In this work we have exploited these new capabilities of scanning x-ray diffraction to investigate cardiac muscle cells as well as cardiac tissue. We give examples of how cardiac cells, especially living, cultured cells, can be prepared to be compatible with the instrumentation constraints of nano- or micro-diffraction instruments. Furthermore, we show how the developmental stage, ranging from neonatal to adult cells, as well as the final preparation state of the cardiomyocytes influences the recorded scattering signal and how these diffraction signals compare to the structure of a fully developed cardiac muscle.

PIND: High spatial resolution by pinhole neutron diffraction

A pinhole neutron diffraction (PIND) technique was developed to enable improving the spatial resolution down to 250 μm. Instead of the conventional engineering diffraction method which integrates all the diffraction signals on the detector plane, the PIND setup utilizes the diffraction pattern of each pixel on 2D detectors. The proposed PIND arrangement enables improving the spatial resolution of time-of-flight instruments and allows solving problems involving steep gradients of strain or texture. The phase content and preferential orientation of grains inside samples can be spatially resolved in 2D/3D. Further, PIND retains the capability of in-situ non-destructive neutron diffraction mapping of lattice strain and grain orientation under external stimuli such as temperature and force.

Thick Filament Mechano-Sensing in Skeletal and Cardiac Muscles: A Common Mechanism Able to Adapt the Energetic Cost of the Contraction to the Task.

A dual regulation of contraction operates in both skeletal and cardiac muscles. The first mechanism, based on Ca2+-dependent structural changes of the regulatory proteins in the thin filament, makes the actin sites available for binding of the myosin motors. The second recruits the myosin heads from the OFF state, in which they are unable to split ATP and bind to actin, in relation to the force during contraction. Comparison of the relevant X-ray diffraction signals marking the state of the thick filament demonstrates that the force feedback that controls the regulatory state of the thick filament works in the same way in skeletal as in cardiac muscles: even if in an isometric tetanus of skeletal muscle force is under the control of the firing frequency of the motor unit, while in a heartbeat force is controlled by the afterload, the stress-sensor switching the motors ON plays the same role in adapting the energetic cost of the contraction to the force. A new aspect of the Frank-Starling law of the heart emerges: independent of the diastolic filling of the ventricle, the number of myosin motors switched ON during systole, and thus the energetic cost of contraction, are tuned to the arterial pressure. Deterioration of the thick-filament regulation mechanism may explain the hyper-contractility related to hypertrophic cardiomyopathy, an inherited heart disease that in 40% of cases is due to mutations in cardiac myosin.

Modified ultrasonic time-of-flight diffraction testing with Barker code excitation for sizing inclined crack

Effectively sizing inclined cracks inside material is a difficult issue in ultrasonic non-destructive testing. To size the length, depth and orientation of inclined crack, a modified ultrasonic time-of-flight diffraction testing with double receivers (DR-TOFD) using Barker code excitation is proposed. The DR-TOFD technique is excited by Barker code, which has accurate time precision, and the diffraction wave of the crack tips is received by two receivers. The diffraction signals are compressed by matched filter to obtain desired detecting signals, which are used to estimate the length, depth and orientation of crack. Finite element method, which simulates wave propagation in specimen with a 6 mm crack with different inclination angles, is used to evaluate the detecting ability of the DR-TOFD with Barker code excitation. The simulation results show that the time precision of the proposed technique is up to 0.01 μs. Experiment is also performed to verify the detecting ability of DR-TOFD. The experiment results show that the proposed technique is able to expediently and accurately size inclined crack.

Single-particle XFEL 3D reconstruction of ribosome-size particles based on Fourier slice matching: requirements to reach subnanometer resolution.

Three-dimensional (3D) structures of biomolecules provide insight into their functions. Using X-ray free-electron laser (XFEL) scattering experiments, it was possible to observe biomolecules that are difficult to crystallize, under conditions that are similar to their natural environment. However, resolving 3D structure from XFEL data is not without its challenges. For example, strong beam intensity is required to obtain sufficient diffraction signal and the beam incidence angles to the molecule need to be estimated for diffraction patterns with significant noise. Therefore, it is important to quantitatively assess how the experimental conditions such as the amount of data and their quality affect the expected resolution of the resulting 3D models. In this study, as an example, the restoration of 3D structure of ribosome from two-dimensional diffraction patterns created by simulation is shown. Tests are performed using the diffraction patterns simulated for different beam intensities and using different numbers of these patterns. Guidelines for selecting parameters for slice-matching 3D reconstruction procedures are established. Also, the minimum requirements for XFEL experimental conditions to obtain diffraction patterns for reconstructing molecular structures to a high-resolution of a few nanometers are discussed.

Single-shot 3D coherent diffractive imaging of core-shell nanoparticles with elemental specificity

We report 3D coherent diffractive imaging (CDI) of Au/Pd core-shell nanoparticles with 6.1 nm spatial resolution with elemental specificity. We measured single-shot diffraction patterns of the nanoparticles using intense x-ray free electron laser pulses. By exploiting the curvature of the Ewald sphere and the symmetry of the nanoparticle, we reconstructed the 3D electron density of 34 core-shell structures from these diffraction patterns. To extract 3D structural information beyond the diffraction signal, we implemented a super-resolution technique by taking advantage of CDI’s quantitative reconstruction capabilities. We used high-resolution model fitting to determine the Au core size and the Pd shell thickness to be 65.0 ± 1.0 nm and 4.0 ± 0.5 nm, respectively. We also identified the 3D elemental distribution inside the nanoparticles with an accuracy of 3%. To further examine the model fitting procedure, we simulated noisy diffraction patterns from a Au/Pd core-shell model and a solid Au model and confirmed the validity of the method. We anticipate this super-resolution CDI method can be generally used for quantitative 3D imaging of symmetrical nanostructures with elemental specificity.