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Two-dimensional X-ray diffraction
Written by one of the pioneers of 2D X-Ray Diffraction, this useful guide covers the fundamentals, experimental methods and applications of two-dimensional x-ray diffraction, including geometry convention, x-ray source and optics, two-dimensional detectors, diffraction data interpretation, and configurations for various applications, such as phase identification, texture, stress, microstructure analysis, crystallinity, thin film analysis and combinatorial screening. Experimental examples in materials research, pharmaceuticals, and forensics are also given. This presents a key resource to researchers in materials science, chemistry, physics, and pharmaceuticals, as well as graduate-level students in these areas.
eBook
Powder diffraction
This PrimeView highlights the use of powder diffraction to characterise crystalline structures.
Journal Article
Bevel-edge epitaxy of ferroelectric rhombohedral boron nitride single crystal
Within the family of two-dimensional dielectrics, rhombohedral boron nitride (rBN) is considerably promising owing to having not only the superior properties of hexagonal boron nitride
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—including low permittivity and dissipation, strong electrical insulation, good chemical stability, high thermal conductivity and atomic flatness without dangling bonds—but also useful optical nonlinearity and interfacial ferroelectricity originating from the broken in-plane and out-of-plane centrosymmetry
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–
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. However, the preparation of large-sized single-crystal rBN layers remains a challenge
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, owing to the requisite unprecedented growth controls to coordinate the lattice orientation of each layer and the sliding vector of every interface. Here we report a facile methodology using bevel-edge epitaxy to prepare centimetre-sized single-crystal rBN layers with exact interlayer ABC stacking on a vicinal nickel surface. We realized successful accurate fabrication over a single-crystal nickel substrate with bunched step edges of the terrace facet (100) at the bevel facet (110), which simultaneously guided the consistent boron–nitrogen bond orientation in each BN layer and the rhombohedral stacking of BN layers via nucleation near each bevel facet. The pure rhombohedral phase of the as-grown BN layers was verified, and consequently showed robust, homogeneous and switchable ferroelectricity with a high Curie temperature. Our work provides an effective route for accurate stacking-controlled growth of single-crystal two-dimensional layers and presents a foundation for applicable multifunctional devices based on stacked two-dimensional materials.
Centimetre-sized single-crystal rhombohedral boron nitride layers are achieved through bevel-edge epitaxy, and the resulting material exhibits robust, homogeneous and switchable ferroelectricity with a high Curie temperature.
Journal Article
Goniometer-based femtosecond crystallography with X-ray free electron lasers
Significance The extremely short and bright X-ray pulses produced by X-ray free-electron lasers unlock new opportunities in crystallography-based structural biology research. Efficient methods to deliver crystalline material are necessary due to damage or destruction of the crystal by the X-ray pulse. Crystals for the first experiments were 5 µm or smaller in size, delivered by a liquid injector. We describe a highly automated goniometer-based approach, compatible with crystals of larger and varied sizes, and accessible at cryogenic or ambient temperatures. These methods, coupled with improvements in data-processing algorithms, have resulted in high-resolution structures, unadulterated by the effects of radiation exposure, from only 100 to 1,000 diffraction images.
The emerging method of femtosecond crystallography (FX) may extend the diffraction resolution accessible from small radiation-sensitive crystals and provides a means to determine catalytically accurate structures of acutely radiation-sensitive metalloenzymes. Automated goniometer-based instrumentation developed for use at the Linac Coherent Light Source enabled efficient and flexible FX experiments to be performed on a variety of sample types. In the case of rod-shaped Cpl hydrogenase crystals, only five crystals and about 30 min of beam time were used to obtain the 125 still diffraction patterns used to produce a 1.6-áÅ resolution electron density map. For smaller crystals, high-density grids were used to increase sample throughput; 930 myoglobin crystals mounted at random orientation inside 32 grids were exposed, demonstrating the utility of this approach. Screening results from cryocooled crystals of β ₂- adrenoreceptor and an RNA polymerase II complex indicate the potential to extend the diffraction resolution obtainable from very radiation-sensitive samples beyond that possible with undulator-based synchrotron sources.
Journal Article
Parallax in angular sensitive powder diffraction tomography
While a few methods for the determination of depth-resolved strain distributions each with inherent limitations are available, tomographic reconstruction has been applied to this problem in only a limited sense. One of the challenges was the potential impact of geometric parallax, which constitutes a non-negligible lateral offset of diffraction information arising from different sample depths at the detector. Here, the effect of parallax was investigated and two main results have emerged. First, the impact of parallax was found to be additive to other offset contributions, which implies a straightforward correction. Second, for tomographic scans utilizing a full 360° rotation parallax has been found to have no impact on reconstructions of angular information.
Journal Article
On the origin of diffuse intensities in fcc electron diffraction patterns
Interpreting diffuse intensities in electron diffraction patterns can be challenging in samples with high atomic-level complexity, as often is the case with multi-principal element alloys. For example, diffuse intensities in electron diffraction patterns from simple face-centred cubic (fcc) and related alloys have been attributed to short-range order
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, medium-range order
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or a variety of different {111} planar defects, including thin twins
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, thin hexagonal close-packed layers
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, relrod spiking
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and incomplete ABC stacking
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. Here we demonstrate that many of these diffuse intensities, including
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{422} and
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{311} in ⟨111⟩ and ⟨112⟩ selected area diffraction patterns, respectively, are due to reflections from higher-order Laue zones. We show similar features along many different zone axes in a wide range of simple fcc materials, including CdTe, pure Ni and pure Al. Using electron diffraction theory, we explain these intensities and show that our calculated intensities of projected higher-order Laue zone reflections as a function of deviation from their Bragg conditions match well with the observed intensities, proving that these intensities are universal in these fcc materials. Finally, we provide a framework for determining the nature and location of diffuse intensities that could indicate the presence of short-range order or medium-range order.
Some of the diffuse intensities observed in electron diffraction patterns of face-centred cubic multi-principal element alloys are due to reflections from higher-order Laue zones.
Journal Article
Enhancing high‐energy powder X‐ray diffraction applications using a PILATUS4 CdTe detector
Hybrid photon counting detectors have significantly advanced synchrotron research. In particular, the introduction of large cadmium telluride‐based detectors in 2015 enabled a whole new range of high‐energy X‐ray measurements. This article describes the specifications of the new PILATUS4 cadmium telluride detector and presents results from prototype testing for high‐energy powder X‐ray diffraction studies conducted at two synchrotrons. The experiments concern time‐resolved in situ solid‐state reactions at MAX IV (Sweden) and fast‐scanning X‐ray diffraction computed tomography of a battery cell at the ESRF (France). The detector's high quantum efficiency up to 100 keV, combined with a maximum frame rate of 4000 Hz, enables fast data collection. This study demonstrates how these capabilities contribute to improved time and spatial resolution in high‐energy powder X‐ray diffraction studies, facilitating advancements in materials, chemical and energy research. Demonstrations are presented of a PILATUS4 CdTe hybrid photon counting detector prototype for high‐energy powder X‐ray diffraction in materials, chemical and energy research at up to 4 kHz frame rate.
Journal Article