IDATEN and G‐SITENNO: GUI‐assisted software for coherent X‐ray diffraction imaging experiments and data analyses at SACLA

Using our custom‐made diffraction apparatus KOTOBUKI‐1 and two multiport CCD detectors, cryogenic coherent X‐ray diffraction imaging experiments have been undertaken at the SPring‐8 Angstrom Compact free electron LAser (SACLA) facility. To efficiently perform experiments and data processing, two software suites with user‐friendly graphical user interfaces have been developed. The first is a program suite named IDATEN, which was developed to easily conduct four procedures during experiments: aligning KOTOBUKI‐1, loading a flash‐cooled sample into the cryogenic goniometer stage inside the vacuum chamber of KOTOBUKI‐1, adjusting the sample position with respect to the X‐ray beam using a pair of telescopes, and collecting diffraction data by raster scanning the sample with X‐ray pulses. Named G‐SITENNO, the other suite is an automated version of the original SITENNO suite, which was designed for processing diffraction data. These user‐friendly software suites are now indispensable for collecting a large number of diffraction patterns and for processing the diffraction patterns immediately after collecting data within a limited beam time.     

Individual GaAs nanorods imaged by coherent X‐ray diffraction

Using scanning X‐ray diffraction microscopy with a spot size of 220 × 600 nm, it was possible to inspect individual GaAs nanorods grown seed‐free through circular openings in a SiN_x mask in a periodic array with 3 µm spacing on GaAs[111]B. The focused X‐ray beam allows the determination of the strain state of individual rods and, in combination with coherent diffraction imaging, it was also possible to characterize morphological details. Rods grown either in the centre or at the edge of the array show significant differences in shape, size and strain state.     

Utilizing broadband X‐rays in a Bragg coherent X‐ray diffraction imaging experiment

A method is presented to simplify Bragg coherent X‐ray diffraction imaging studies of complex heterogeneous crystalline materials with a two‐stage screening/imaging process that utilizes polychromatic and monochromatic coherent X‐rays and is compatible with in situ sample environments. Coherent white‐beam diffraction is used to identify an individual crystal particle or grain that displays desired properties within a larger population. A three‐dimensional reciprocal‐space map suitable for diffraction imaging is then measured for the Bragg peak of interest using a monochromatic beam energy scan that requires no sample motion, thus simplifying in situ chamber design. This approach was demonstrated with Au nanoparticles and will enable, for example, individual grains in a polycrystalline material of specific orientation to be selected, then imaged in three dimensions while under load.     

Retrieval of the atomic displacements in the crystal from the coherent X‐ray diffraction pattern

The retrieval of spatially resolved atomic displacements is investigated via the phases of the direct(real)‐space image reconstructed from the strained crystal's coherent X‐ray diffraction pattern. It is demonstrated that limiting the spatial variation of the first‐ and second‐order spatial displacement derivatives improves convergence of the iterative phase‐retrieval algorithm for displacements reconstructions to the true solution. This approach is exploited to retrieve the displacement in a periodic array of silicon lines isolated by silicon dioxide filled trenches.     

Hard X‐ray phase‐contrast tomography of non‐homogeneous specimens: grating interferometry versus propagation‐based imaging

X‐ray phase‐contrast imaging is an effective approach to drastically increase the contrast and sensitivity of microtomographic techniques. Numerous approaches to depict the real part of the complex‐valued refractive index of a specimen are nowadays available. A comparative study using experimental data from grating‐based interferometry and propagation‐based phase contrast combined with single‐distance phase retrieval applied to a non‐homogeneous sample is presented (acquired at beamline ID19‐ESRF). It is shown that grating‐based interferometry can handle density gradients in a superior manner. The study underlines the complementarity of the two techniques for practical applications.     

Exploring experimental parameter choice for rapid speckle‐tracking phase‐contrast X‐ray imaging with a paper analyzer

Phase‐contrast X‐ray imaging using a paper analyzer enables the visualization of X‐ray transparent biological structures using the refractive properties of the sample. The technique measures the sample‐induced distortions of a spatially random reference pattern to retrieve quantitative sample information. This phase‐contrast method is promising for biomedical application due to both a simple experimental set‐up and a capability for real‐time imaging. The authors explore the experimental configuration required to achieve robustness and accuracy in terms of (i) the paper analyzer feature size, (ii) the sample‐to‐detector distance, and (iii) the exposure time. Results using a synchrotron source confirm that the technique achieves accurate phase retrieval with a range of paper analyzers and at exposures as short as 0.5 ms. These exposure times are sufficiently short relative to characteristic physiological timescales to enable real‐time dynamic imaging of living samples. A theoretical guide to the choice of sample‐to‐detector distance is also derived. While the measurements are specific to the set‐up, these guidelines, the example speckle images, the strategies for analysis in the presence of noise and the experimental considerations and discussion will be of value to those who wish to use the speckle‐tracking paper analyzer technique.     

Spectrometer for hard X‐ray free‐electron laser based on diffraction focusing

X‐ray free‐electron lasers (XFELs) generate sequences of ultra‐short spatially coherent pulses of X‐ray radiation. A diffraction focusing spectrometer (DFS), which is able to measure the whole energy spectrum of the radiation of a single XFEL pulse with an energy resolution of ΔE/E? 2 × 10^?6, is proposed. This is much better than for most modern X‐ray spectrometers. Such resolution allows one to resolve the fine spectral structure of the XFEL pulse. The effect of diffraction focusing occurs in a single‐crystal plate due to dynamical scattering, and is similar to focusing in a Pendry lens made from a metamaterial with a negative refraction index. Such a spectrometer is easier to operate than those based on bent crystals. It is shown that the DFS can be used in a wide energy range from 5 keV to 20 keV.     

Coherent X‐ray diffractive imaging of protein crystals

The technique of coherent X‐ray diffraction imaging (CXDI) has recently shown great promise for the study of inorganic nanocrystals. In this work the CXDI method has been applied to the study of micrometer‐size protein crystals. Finely sampled diffraction patterns of single crystals were measured and iterative phase‐retrieval algorithms were used to reconstruct the two‐dimensional shape of the crystal. The density maps have limited reproducibility because of radiation damage, but show clear evidence for crystal facets. Qualitative analysis of a number of single‐crystal diffraction peaks indicates the presence of inward surface contraction on 2 µm size crystals. A survey of several hundred diffraction patterns yielded a number of examples with dramatic single‐sided streaks, for which a plausible model is constructed.     

Hard X‐ray phase‐contrast imaging with the Compact Light Source based on inverse Compton X‐rays

The first imaging results obtained from a small‐size synchrotron are reported. The newly developed Compact Light Source produces inverse Compton X‐rays at the intersection point of the counter propagating laser and electron beam. The small size of the intersection point gives a highly coherent cone beam with a few milliradian angular divergence and a few percent energy spread. These specifications make the Compact Light Source ideal for a recently developed grating‐based differential phase‐contrast imaging method.     

Novel silica stabilization method for the analysis of fine nanocrystals using coherent X‐ray diffraction imaging

High‐energy X‐ray Bragg coherent diffraction imaging (BCDI) is a well established synchrotron‐based technique used to quantitatively reconstruct the three‐dimensional morphology and strain distribution in nanocrystals. The BCDI technique has become a powerful analytical tool for quantitative investigations of nanocrystals, nanotubes, nanorods and more recently biological systems. BCDI has however typically failed for fine nanocrystals in sub‐100 nm size regimes – a size routinely achievable by chemical synthesis – despite the spatial resolution of the BCDI technique being 20–30 nm. The limitations of this technique arise from the movement of nanocrystals under illumination by the highly coherent beam, which prevents full diffraction data sets from being acquired. A solution is provided here to overcome this problem and extend the size limit of the BCDI technique, through the design of a novel stabilization method by embedding the fine nanocrystals into a silica matrix. Chemically synthesized FePt nanocrystals of maximum dimension 20 nm and AuPd nanocrystals in the size range 60–65 nm were investigated with BCDI measurement at beamline 34‐ID‐C of the APS, Argonne National Laboratory. Novel experimental methodologies to elucidate the presence of strain in fine nanocrystals are a necessary pre‐requisite in order to better understand strain profiles in engineered nanocrystals for novel device development.     

A method of hard X‐ray phase‐shifting digital holography

A new method of phase‐shifting digital holography is demonstrated in the hard X‐ray region. An in‐line‐type phase‐shifting holography setup was installed in a 6.80 keV hard X‐ray synchrotron beamline. By placing a phase plate consisting of a hole and a band at the focusing point of a Fresnel lens, the relative phase of the reference and objective beams could be successfully shifted for use with a three‐step phase‐shift algorithm. The system was verified by measuring the shape of a gold test pattern and a silica sphere.     

In situ X‐ray diffraction study on the growth kinetics of NiO nanoparticles

The growth kinetics of NiO nanoparticles have been studied by in situ X‐ray diffraction using two detection systems (conventional and imaging plate). NiO nanoparticles were formed by thermal decomposition after heating of an amorphous compound formed by the coprecipitation method. It was found that the detection method using an imaging plate is more efficient than the conventional detection mode for observing changes in the crystallite growth of nanocrystalline materials. Studies have been carried out to investigate the effects of the heating rates on the particles growth. The results suggest that the growth process of the particles is accelerated when the samples are treated at low heating rates. The evolution of particles size and the diffusion coefficient obtained from X‐ray powder diffraction patterns are discussed in terms of the thermal conditions for the two types of detection.     

Application of an ePix100 detector for coherent scattering using a hard X‐ray free‐electron laser

A prototype ePix100 detector was used in small‐angle scattering geometry to capture speckle patterns from a static sample using the Linac Coherent Light Source (LCLS) hard X‐ray free‐electron laser at 8.34 keV. The average number of detected photons per pixel per pulse was varied over three orders of magnitude from about 23 down to 0.01 to test the detector performance. At high average photon count rates, the speckle contrast was evaluated by analyzing the probability distribution of the pixel counts at a constant scattering vector for single frames. For very low average photon counts of less than 0.2 per pixel, the `droplet algorithm' was first applied to the patterns for correcting the effect of charge sharing, and then the pixel count statistics of multiple frames were analyzed collectively to extract the speckle contrast. Results obtained using both methods agree within the uncertainty intervals, providing strong experimental evidence for the validity of the statistical analysis. More importantly it confirms the suitability of the ePix100 detector for X‐ray coherent scattering experiments, especially at very low count rates with performances surpassing those of previously available LCLS detectors.     

Diffraction of X‐ray free‐electron laser femtosecond pulses on single crystals in the Bragg and Laue geometry

A solution of the problem of dynamical diffraction for X‐ray pulses with arbitrary dimensions in the Bragg and Laue cases in a crystal of any thickness and asymmetry coefficient of reflection is presented. Analysis of pulse form and duration transformation in the process of diffraction and propagation in a vacuum is conducted. It is shown that only the symmetrical Bragg case can be used to avoid smearing of reflected pulses.     

Design and application of a high‐temperature microfurnace for an in situ X‐ray diffraction study of phase transformation

Thermal treatment of mineral ores such as ilmenite can initiate phase transformations that could affect their activation or deactivation, subsequently influencing their ability to dissolve in a leaching agent. Most laboratory‐based X‐ray diffraction (XRD) studies were carried out ex situ in which realistic diffraction patterns could not be obtained simultaneously with occurring reactions and were time‐consuming. The availability of synchrotron‐radiation‐based XRD not only allows in situ analysis, but significantly shortens the data recording time. The present study details the design of a robust high‐temperature microfurnace which allows thermal processing of mineral ore samples and the simultaneous collection of high‐resolution synchrotron XRD data. In addition, the application of the manufactured microfurnace for in situ study of phase transformations of ilmenite ore under reducing conditions is demonstrated.     

X‐ray focusing by the system of refractive lens(es) placed inside asymmetric channel‐cut crystals

An X‐ray one‐dimensionally focusing system, a refracting–diffracting lens (RDL), composed of Bragg double‐asymmetric‐reflecting two‐crystal plane parallel plates and a double‐concave cylindrical parabolic lens placed in the gap between the plates is described. It is shown that the focal length of the RDL is equal to the focal distance of the separate lens multiplied by the square of the asymmetry factor. One can obtain RDLs with different focal lengths for certain applications. Using the point‐source function of dynamic diffraction, as well as the Green function in a vacuum with parabolic approximation, an expression for the double‐diffracted beam amplitude for an arbitrary incident wave is presented. Focusing of the plane incident wave and imaging of a point source are studied. The cases of non‐absorptive and absorptive lenses are discussed. The intensity distribution in the focusing plane and on the focusing line, and its dependence on wavelength, deviation from the Bragg angle and magnification is studied. Geometrical optical considerations are also given. RDLs can be applied to focus radiation from both laboratory and synchrotron X‐ray sources, for X‐ray imaging of objects, and for obtaining high‐intensity beams. RDLs can also be applied in X‐ray astronomy.     

Implementation of ultrafast X‐ray diffraction at the 1W2B wiggler beamline of Beijing Synchrotron Radiation Facility

The implementation of a laser pump/X‐ray probe scheme for performing picosecond‐resolution X‐ray diffraction at the 1W2B wiggler beamline at Beijing Synchrotron Radiation Facility is reported. With the hybrid fill pattern in top‐up mode, a pixel array X‐ray detector was optimized to gate out the signal from the singlet bunch with interval 85 ns from the bunch train. The singlet pulse intensity is ～2.5 × 10⁶ photons pulse^?1 at 10 keV. The laser pulse is synchronized to this singlet bunch at a 1 kHz repetition rate. A polycapillary X‐ray lens was used for secondary focusing to obtain a 72 µm (FWHM) X‐ray spot. Transient photo‐induced strain in BiFeO₃ film was observed at a ～150 ps time resolution for demonstration.     

Three‐dimensional imaging of chemical phase transformations at the nanoscale with full‐field transmission X‐ray microscopy

The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano‐ and micrometer‐scale factors at the origin of macroscopic behavior. While different electron‐ and X‐ray‐based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X‐ray imaging set‐up is proposed, combining full‐field transmission X‐ray microscopy (TXM) with X‐ray absorption near‐edge structure (XANES) spectroscopy to follow two‐dimensional and three‐dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields.     

Radiation damage to protein specimens from electron beam imaging and diffraction: a mini‐review of anti‐damage approaches,with special reference to synchrotron X‐ray crystallography

Recent research progress using X‐ray cryo‐crystallography with the photon beams from third‐generation synchrotron sources has resulted in recognition that this intense radiation commonly damages protein samples even when they are held at 100 K. Other structural biologists examining thin protein crystals or single particle specimens encounter similar radiation damage problems during electron diffraction and imaging, but have developed some effective countermeasures. The aim of this concise review is to examine whether analogous approaches can be utilized to alleviate the X‐ray radiation damage problem in synchrotron macromolecular crystallography. The critical discussion of this question is preceded by presentation of background material on modern technical procedures with electron beam instruments using 300–400 kV accelerating voltage, low‐dose exposures for data recording, and protection of protein specimens by cryogenic cooling; these practical approaches to dealing with electron radiation damage currently permit best resolution levels of 6 Å (0.6 nm) for single particle specimens, and of 1.9 Å for two‐dimensional membrane protein crystals. Final determination of the potential effectiveness and practical value of using such new or unconventional ideas will necessitate showing, by experimental testing, that these produce significantly improved protection of three‐dimensional protein crystals during synchrotron X‐ray diffraction.     

In situ synchrotron high‐energy X‐ray diffraction analysis on phase transformations in Ti–Al alloys processed by equal‐channel angular pressing

Mixtures of 47‐Al and 53‐Ti powders (atomic %) have been consolidated using back pressure equal‐channel angular pressing starting with both raw and ball‐milled powders. In situ synchrotron high‐energy X‐ray diffraction studies are presented with continuous Rietveld analysis obtained upon a heating ramp from 300 K to 1075 K performed after the consolidation process. Initial phase distributions contain all intermetallic compounds of this system except Al, with distribution maxima in the outer regions of the concentrations (α‐Ti, TiAl₃). Upon annealing, the phase evolution and lattice parameter changes owing to chemical segregation, which is in favour for the more equilibrated phases such as γ‐TiAl, α₂‐Ti₃Al and TiAl₂, were followed unprecedentedly in detail. An initial δ‐TiH₂ content with a phase transition at about 625 K upon heating created an intermediate β‐Ti phase which played an important role in the reaction chain and gradually transformed into the final products.