High-quality Diffraction Research Articles

<i>In Situ</i> Gas Supply System on the Powder Diffraction Beamline I11 at Diamond Light Source

Beamline I11 at Diamond began accepting users for high resolution powder diffraction experiments in Oct 2008. We present the design, key specifications, performance and the hardware of this new beamline which receives an intense and highly collimated x-ray beam generated by an in-vacuum undulator. With the simple optics (a double-crystal monochromator, harmonic rejection mirrors and slits), a high purity beam of low energy-bandpass X-rays optimised at 15 keV is delivered at the sample. The heavy duty diffraction instrument is designed to have the flexibility to house a variety of sample environments and holds two detection systems to collect high quality diffraction data, i.e. multi-analysing crystals (MAC) for high angular resolution experiments and a fast position sensitive detector (PSD) for time-resolved studies. A recent addition to the beamline capabilities is the installation of a specifically designed gas control system. This allows the in-situ dosing of a powder sample with gases such as hydrogen and carbon dioxide, at low (~10 mbar) and high pressures (<100 bar). In addition a low pressure capillary sample cell is described which is now available to users of the beamline.

Probing hydrogen positions in hydrous compounds: information from parametric neutron powder diffraction studies

We demonstrate the extent to which modern detector technology, coupled with a high flux constant wavelength neutron source, can be used to obtain high quality diffraction data from short data collections, allowing the refinement of the full structures (including hydrogen positions) of hydrous compounds from in situ neutron powder diffraction measurements. The in situ thermodiffractometry and controlled humidity studies reported here reveal that important information on the reorientations of structural water molecules with changing conditions can be easily extracted, providing insight into the effects of hydrogen bonding on bulk physical properties. Using crystalline BaCl2·2H2O as an example system, we analyse the structural changes in the compound and its dehydration intermediates with changing temperature and humidity levels to demonstrate the quality of the dynamic structural information on the hydrogen atoms and associated hydrogen bonding that can be obtained without resorting to sample deuteration.

Effect of high pressure on the crystal structure and electronic properties of magnetite below 25 GPa

We report results from high-pressure single-crystal X-ray diffraction and Mössbauer absorption experiments on magnetite. Based on high-quality diffraction data, we have obtained accurate information on the crystal structure of magnetite below 25 GPa, which enables an unambiguous interpretation of the Mössbauer data using constrained area ratios and a full transmission integral fit that avoids area distortion due to thickness effects. Based on our analysis, all aspects of the electronic and magnetic properties of magnetite reported previously below 25 GPa at ambient temperature can be explained solely by the enhanced delocalization of 3d electrons of iron atoms. For instance, we present evidence that the compression-induced metallization changes the sign of the charge carrier spin polarization at 15 GPa.

Performance and early applications of a versatile double aberration-corrected JEOL-2200FS FEG TEM/STEM at Aalto University

Applications relevant to carbon based nano-materials have been explored using a newly installed JEOL-2200FS field emission gun (FEG) (scanning) transmission electron microscope (S)TEM which is integrated with two CEOS aberration correctors for both the TEM image-forming and the STEM probe-forming lenses. The performance and utility of this newly commission hardware has been reviewed with a particular focus on operation at an acceleration voltage of 80kV, thus bringing the primary electron beam voltage below the knock-on threshold for carbon materials and opening up a range of possibilities for the study of carbon-based nanostructures in the aberration-corrected electron microscope. The ability of the microscope to obtain both atomic TEM images and high-quality electron diffraction patterns from carbon nanotubes was demonstrated. The chiral structure of a double-walled carbon nanotube was determined from its diffraction pattern. The aberration corrected TEM imaging technique facilitates a unique approach to accurate determination of single-walled carbon nanotube diameters. On the other hand, the probe-corrected high angle annular dark field (HAADF) STEM imaging performance allows for the detection of single gold atoms at 80kV and was used to study the graphite interlayer spacing in a multi-walled carbon nanotube.

Variability in sepiolite: Diffraction studies

Twenty sepiolites of known composition from different origins were analyzed to quantify the variability in structural parameters and its possible relationships with composition and morphology. Morphology SEM analyses led to classify the sepiolites into several groups, beyond the two simple macroscopic or clay groups. X-ray powder diffraction with synchrotron light was used to discuss the variability of the a and b cell parameters with the nature of the cations and occupancy of the octahedral shell. Rietveld refinement using the ideal sepiolite model is performed on sepiolites at two temperatures: 225 °C (for zeolitically dehydrated sepiolite) and 25 °C (for hydrated ambient sepiolite). The latter permitted to locate ca. six molecules of the zeolitic H2O within the tunnels. A few samples were selected to evaluate the feasibility and potential of single-crystal diffraction methods: X-ray microdiffraction and electron diffraction. The macroscopic sepiolites gave well-structured and rich X-ray fiber diffraction patterns, in excellent agreement with ab initio simulations. High-quality single-crystal electron diffraction patterns for three axis zones are indexed and compared with simulations. The experimental and modeling results for X-ray microdiffraction and electron diffraction open a new path for quantitative crystallography on sepiolite and other fibrous clays from the sepiolite-palygorskite group.

Transmission-electron diffraction by MeV electron pulses

We have developed a compact ultrafast electron diffractometer, consisting of a laser-driven rf photocathode that generates 3.0 MeV probe electron pulses, three-stage lens optics, and a custom-built detector for relativistic electrons. High-quality single-shot transmission electron diffraction has been detected from 180-nm-thick Si single crystals, with an excellent special resolution for diffracted beams; the spot width of 0.02 A−1 is obtained. The pulse width is estimated to be 100 fs in duration. Characteristics of the electron beam and other diffractometer features are discussed.

Moiré Interferometry Assessement of Residual Stress Variation in Depth on a Shot Peened Surface

Abstract: The main goal of this work was the development of experimental techniques to measure in depth non‐uniform residual stresses, as alternative to the more conventional hole‐drilling method with strain gauges. The proposed experimental methodology is based on moiré interferometry. This high resolution field technique allows in‐plane displacement assessment without contact. Grating replication techniques were also developed to record high quality diffraction gratings onto the specimen’s surface. A laser interferometry setup was implemented to generate the master grating (virtual). The stress relaxation was promoted by blind hole‐drilling and the obtained fringe patterns were video recorded. Image processing techniques were applied to assess the in‐plane strain full‐field. A finite elements code (FEM), ANSYS®, was used to simulate the stress relaxation process and to calculate the hole‐drilling calibration constants.

Macromolecular microcrystallography

Over a decade has passed since pioneering diffraction experiments on macromolecular microcrystals were performed at the European Synchrotron Radiation Facility. Since then the measurement of high-quality diffraction data for the purpose of structure determination has been transformed from a specialized experiment into routine practice at dedicated microfocus macromolecular crystallography beamlines at synchrotron facilities. In this article, we review the evolution of microfocus macromolecular crystallography over the past two decades, and explore the instrumentation and methodologies that have evolved to enable structure determination in the face of unfavourable odds. Several case studies are reviewed in depth illustrating the power of microcrystallography and microfocus instruments and their application in answering important biological questions. Challenges and limitations currently facing the community and areas of future development and problems that must be addressed in the future are also discussed.

Preparation of metallic samples for electron backscatter diffraction and its influence on measured misorientation

Preparation of specimens for electron backscatter diffraction has to be done with great care to ensure a high indexing fraction from high-quality patterns. Despite the amount of published and recommended preparation methods for different materials, detailed information about the preparation parameters are either missing, or different preparation methods are recommended for one material. The aim of this contribution is to compare the application of several preparation techniques on different metallic samples to determine a suitable preparation method for high-quality electron backscatter diffraction measurements for a variety of alloys. From the results obtained, polishing with an oxide polishing suspension is the most appropriate preparation method for the materials and preparation methods investigated. Furthermore, the influence of mechanical polishing as well as of oxide polishing suspension polishing on misorientation is found to be negligible for misorientation angles greater than 1°. In the course of this study the absolute indexing reproducibility of the EBSD-system employed was determined to be 1.18° with respect to the misorientation angle θ.

Electron density distribution in vanadium and niobium fromγ-ray diffraction

The electron density distribution in paramagnetic vanadium and niobium is derived via multipole refinement of high-quality single-crystal diffraction data, complete up to sin\ensuremath{\theta}/\ensuremath{\lambda} $=$ 1.9 \AA{}${}^{\ensuremath{-}1}$, collected at room temperature with 316.5 keV $\ensuremath{\gamma}$ radiation. Four $\ensuremath{\gamma}$ lines in the energy range 200--600 keV have been used to extrapolate extinction-free low-order structure factors. Both metals display charge asphericity due to preferential occupancy of the ${t}_{2g}$ orbital. The asphericity in V is in quantitative agreement with ab initio calculations, but not with earlier experimental results, laying at rest a long-standing debate. In both metals, the $d$-electron density is strongly contracted relative to the free atoms. The high-precision thermal parameters are in good agreement with some of the older results. No support is found in the data for anharmonic contributions to the thermal parameters, contrary to claims in previous reports on V. Attention is paid to the 3$d$-4$s$ occupation problem in V, indicating no change in electronic configuration between atom and metal. Relativistic form factor issues are also discussed. It is pointed out that for the analysis of crystallographic data nonrelativistic form factors are to be preferred over their relativistic counterparts.

Single mimivirus particles intercepted and imaged with an X-ray laser

X-ray lasers offer new capabilities in understanding the structure of biological systems, complex materials and matter under extreme conditions. Very short and extremely bright, coherent X-ray pulses can be used to outrun key damage processes and obtain a single diffraction pattern from a large macromolecule, a virus or a cell before the sample explodes and turns into plasma. The continuous diffraction pattern of non-crystalline objects permits oversampling and direct phase retrieval. Here we show that high-quality diffraction data can be obtained with a single X-ray pulse from a non-crystalline biological sample, a single mimivirus particle, which was injected into the pulsed beam of a hard-X-ray free-electron laser, the Linac Coherent Light Source. Calculations indicate that the energy deposited into the virus by the pulse heated the particle to over 100,000 K after the pulse had left the sample. The reconstructed exit wavefront (image) yielded 32-nm full-period resolution in a single exposure and showed no measurable damage. The reconstruction indicates inhomogeneous arrangement of dense material inside the virion. We expect that significantly higher resolutions will be achieved in such experiments with shorter and brighter photon pulses focused to a smaller area. The resolution in such experiments can be further extended for samples available in multiple identical copies.

Coherent diffraction microscopy at SPring-8: instrumentation, data acquisition and data analysis.

Since the first demonstration of coherent diffraction microscopy in 1999, this lensless imaging technique has been experimentally refined by continued developments. Here, instrumentation and experimental procedures for measuring oversampled diffraction patterns from non-crystalline specimens using an undulator beamline (BL29XUL) at SPring-8 are presented. In addition, detailed post-experimental data analysis is provided that yields high-quality image reconstructions. As the acquisition of high-quality diffraction patterns is at least as important as the phase-retrieval procedure to guarantee successful image reconstructions, this work will be of interest for those who want to apply this imaging technique to materials science and biological samples.

Initial microstructural study of a Ce–La alloy using electron backscattered diffraction

To better understand and exploit the unique electronic and structural properties of f-block metals and their alloys it is perceived that an improved knowledge of the microstructural characteristics and phase changes as a function of temperature and pressure, is necessary. For other different types of metallic systems, the use of electron back-scattered diffraction (EBSD) is becoming a common practice in order to obtain detailed microstructural information, but this has, as yet, been very limited in case of f-block metals. Because of their extreme affinity to oxygen and rapid surface reaction, EBSD studies of this metal-category are very sparse with only one work published on cerium metal providing an example of technical hurdles for a prerequisite oxide-free metal surface. Specifically the need to remove the oxide by ion etching was considered essential to enable a successful EBSD analysis. The current work presents the results of a first attempt to characterise the microstructure of a Ce–La alloy using EBSD. It demonstrates that high quality diffraction patterns and crystal orientation maps can be successfully obtained following a carefully controlled preparation of the alloy surface in the open laboratory by applying a simple and reproducible electro-polishing procedure without a further need for ion etching in vaccuo.

High-throughput powder diffraction on beamline I11 at Diamond

A new capability designed for high-throughput (HT) structural analysis using the synchrotron powder diffraction beamline (I11) at Diamond Light Source is reported. With a high-brightness X-ray beam, multi-analyser detectors and fast data-acquisition procedures, high-quality diffraction data can be collected at a speed of ∼15–30 min per powder pattern for good crystalline materials. Fast sample changing at a rate of a few seconds per specimen is achieved with a robotic arm and pre-loaded capillary specimens on a multi-tray carousel (200-sample capacity). Additional equipment, such as an automatic powder-loading machine and a pre-alignment jig for the sample capillaries, is available to reduce preparation time. For demonstration purposes, the first results presented here are those from standard reference powders of Si, TiO2and TiO2/Si mixtures, obtained by analysing the data using Le Bail (instrumental calibration) and Rietveld refinements (quantitative agreement within 1%). The HT hardware was then used to study the structural phase evolution of a library of 31 La4Ni3−xFexO10heterometallic ceramic powders in less than 1 d. The powders were generated from a single heat treatment (at 1348 K in air for 12 h) of nanoceramic oxide co-precipitate precursors, made using a newly developed HT synthesis robot. Crystallographic details (symmetry and lattice parameters) were obtained as a function of Fe concentration. The results revealed that this approach was able to produce a pure Ruddlesden–Popper-type phase with an iron content of up tox= 0.5, significantly higher than has been achieved previously using more conventional synthesis routes and thus demonstrating the power of using the HT approach.

Magneto structural transition in the DySi CrB- and micro-structural changes in the FeB-type compounds by XRPD and neutron diffraction

We present the magnetic temperature phase diagrams of the CrB- and FeB-type orthorhombic phases of the DySi compound, determined from high-quality powder XRPD and neutron diffraction, as well as the sample microstructure as determined by HRTEM. Both phase diagrams comprise a HT (Tc1, Tc2−TN) and a LT range (5K–Tc1, Tc2) separated by a monoclinic phase transition at Tc1=Tc2=23.5K well below the second-order Néel transition (TN=40K). The transition paths are for CrB-type Cmcm (HT) Tc1→C2/m11 (LT), and for FeB Pnma (HT) Tc2→P21/n11 (LT). The transitions are related to non-monotonous changes of the lattice and structural parameters displaying anomalies at Tc1, Tc2 and slight volume changes. For the CrB-type the monoclinic angle decreases smoothly from Tc1 down to 5K and the maximum strain experienced by the crystal lattice in the (021) direction was found at Tc1.In the FeB-type, in addition to the magneto-elastic transition at Tc2=23.5K, minor anomalies are found at 13.5K in the temperature dependence of the monoclinic angle and the maximum strain along (011). Both temperatures mark the sequence of changes in the magnetic domain microstructure observed in FeB: below T2=23.5K the incommensurate HT magnetic phase with q3≈(01217) disproportionates into two LT phases q3≈(012111)T2 and q2≈(01216) coexisting in the form of domains with portions varying with T going from T2 down to 13.5K (q2 increasing at the cost of q3). This behaviour could be related to structural inhomogeneities below the first-order magneto-elastic transition Tc2, if one assumes a broad two phase range, where the HT (Pnma) phase coexists with (P21/n) as a metastable phase at LT in the form of domains with different magnetic behaviour.

Single-crystal Raman spectroscopy and X-ray crystallography at beamline X26-C of the NSLS

Three-dimensional structures derived from X-ray diffraction of protein crystals provide a wealth of information. Features and interactions important for the function of macromolecules can be deduced and catalytic mechanisms postulated. Still, many questions can remain, for example regarding metal oxidation states and the interpretation of `mystery density', i.e. ambiguous or unknown features within the electron density maps, especially at ∼2 Å resolutions typical of most macromolecular structures. Beamline X26-C at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL), provides researchers with the opportunity to not only determine the atomic structure of their samples but also to explore the electronic and vibrational characteristics of the sample before, during and after X-ray diffraction data collection. When samples are maintained under cryo-conditions, an opportunity to promote and follow photochemical reactions in situ as a function of X-ray exposure is also provided. Plans are in place to further expand the capabilities at beamline X26-C and to develop beamlines at NSLS-II, currently under construction at BNL, which will provide users access to a wide array of complementary spectroscopic methods in addition to high-quality X-ray diffraction data.

Effect of Water Vapor Sorption on Local Structure of Poly(vinylpyrrolidone)

The effect of water vapor sorption on the local structure of poly(vinylpyrrolidone) (PVP), was investigated using high-quality X-ray powder diffraction (XRPD). To examine the effects on molecular scale structure due to polymer chain length and water sorption, different molecular weights of PVP were studied at ambient temperature and different controlled relative humidities. Sorption of water determined gravimetrically on drying and changes to the glass-transition temperature (T(g)) measured by modulated differential scanning calorimetry (mDSC) were found to be consistent with previous reports. The XRPD results show that the position of the high- and low-angle halos for PVP change with the sorption of water. The corresponding characteristic scattering distances display a strong correlation with the measured water content and to T(g). Chemometric analysis was also performed to extract water content information from XRPD data and obtained results are correlated with the values measured gravimetrically, which lends support for the apparent clustering of water in PVP drawn by other techniques.

In situ viscometry of high-pressure melts in the Paris–Edinburgh cell: application to liquid FeS

Knowledge of the viscosity of high-pressure melts is important in various domains of research, such as geosciences or materials science. Experimentally, the viscosity of liquids can be determined using the falling sphere technique. This method has been developed at high pressures and high temperatures at Beamline ID27 of the European Synchrotron Radiation Facility (ESRF), combining a Paris–Edinburgh cell with in situ X-ray radiography. The press is interfaced to Soller slits and imaging systems to measure high-quality diffraction patterns and high-resolution X-ray images of the sample. The viscosity of the liquid is derived from the velocity of a dense sphere falling through the pressurized melt and the Stokes law. An optimized two-circle diffractometer allows for moving the press upside down in order to perform a series of measurements on a single sample. The simultaneous collection of X-ray diffraction data on liquids offers the unique opportunity of investigating the relations between viscosity and the structure of melts. The potential of this new equipment is illustrated on the example of FeS melt viscosity and its implications for the Earth's core.

Preliminary crystallographic analysis of the N-terminal domain of FILIA, a protein essential for embryogenesis.

FILIA is a component of the subcortical maternal complex that is essential for early stage embryogenesis. Its 6xHis-tagged N-terminal domain was expressed in Escherichia coli and purified to homogeneity. Two types of crystals formed under different crystallization conditions during screening. Orthorhombic crystals appeared in a solution containing 1.4 M ammonium sulfate, 0.1 M Tris pH 8.2 and 12% glycerol, while tetragonal crystals were obtained using 15% PEG 4000 mixed with 0.1 M HEPES pH 7.5 and 15% 2-propanol. High-quality diffraction data were collected from the two crystal forms to resolutions of 1.8 and 2.2 A, respectively, using synchrotron radiation. The Matthews coefficients indicated that the P2(1)2(1)2(1) and P4(1)2(1)2 crystals contained two molecules and one molecule per asymmetric unit, respectively. A selenomethionine-substituted sample failed to crystallize under the native conditions, but another orthorhombic crystal form was obtained under different conditions and anomalous diffraction data were collected.

Nanovolume optimization of protein crystal growth using the microcapillary protein crystallization system.

The Microcapillary Protein Crystallization System (MPCS) is a microfluidic, plug-based crystallization technology that generates X-ray diffraction-ready protein crystals in nanolitre volumes. In this study, 28 out of 29 (93%) proteins crystallized by traditional vapor diffusion experiments were successfully crystallized by chemical gradient optimization experiments using the MPCS technology. In total, 90 out of 120 (75%) protein/precipitant combinations leading to initial crystal hits from vapor diffusion experiments were successfully crystallized using MPCS technology. Many of the resulting crystals produced high-quality X-ray diffraction data, and six novel protein structures that were derived from crystals harvested from MPCS CrystalCards are reported.