June 2017 issue
The latest virtual special issue of Journal of Applied Crystallography features some highlights of the 13th Biennial Conference on High-Resolution X-ray Diffraction and Imaging (XTOP 2016), held in Brno, Czech Republic, in September 2016.
Coherent X-ray diffraction imaging was used to detect a threefold rotational symmetry in hexagonally shaped single semiconductor nanowires. The core–shell–shell structure was resolved by probing symmetric hhh Bragg reflections.
Interfacial roughness is considered as a transition layer. A method of calculation of diffraction scans from multilayered structures with interfacial roughness, which is both fast and free of numerical errors, is developed.
X-ray phase measurements have been applied to study hydrogen bonds and radiation damage in amino acid crystals.
Multi-waveguide interference can be verified experimentally by reconstructing the near-field from the measured far-field diffraction pattern. This enables a direct visualization of the near-field interference pattern and the diversity of fields that can be created by multi-waveguide design, in particular a secondary quasi-focal spot. Numerical propagation using the design parameters is compared with the phase retrieval results.
This article describes interface-sensitive imaging of heterogeneous thin films by an image reconstruction aided X-ray reflectivity technique with an 8 mm-wide parallel beam; the possibility of extracting micro-X-ray reflectivity profiles from the same data collection is discussed.
Opportunities of multi-beam X-ray diffraction are demonstrated for determination of lattice strains in heterostructures and multi-layered systems.
The practical application of the modified Berg–Barrett topographic method in a skew asymmetric scheme of X-ray diffraction is presented. The method is used for the study of the defect structure of CdTe crystals and Cd1−xHgxTe/CdTe epitaxial layers after the influence of different external factors (ion implantation and etching).
Combined ultra-small-, small- and wide-angle X-ray scattering (USAXS–SAXS–WAXS) provides in situ evaluation of the precipitate size distribution (PSD) and phase structure temporal evolution during heat treatment. A method for extraction of an arbitrary PSD in the presence of interparticle interactions is described and illustrated for study of PSD evolution.
The lognormal particle size distributions of supported nanoparticles were obtained from their pair distribution function and the results were validated with scanning transmission electron microscopy.
For the first time, high-temperature evolution of the crystal texture in porous synthetic cordierite was observed by neutron diffraction. The data quality allowed determination of the lattice structure evolution, which turns out to be more significant than the crystal texture change as a function of temperature.
A good quality bulk-size sulphamic acid single crystal was grown by adopting a newly designed seed rotation technique. The crystalline perfection of the grown crystal was assessed using high-resolution X-ray diffraction and it was found to produce a single-peak rocking curve with an FWHM of 8.0′′. The optical, thermal and shock damage threshold behaviours of the crystal have been measured to assess its optimization for device fabrication.
This paper describes the multiaxial texture of zirconia sinters used as metering nozzles and describes the correct method of phase composition determination using X-ray diffraction. Owing to phase composition changes during sample preparation, testing should be carried out on solid samples and the results corrected.
A Bayesian approach to formulation of a search–match strategy for powder phase identification is proposed. Even for a simple exponential model of prior probabilities the approach provides good agreement with known results for several testing examples.
Efficient luminescence energy transfer in doped orthovanadate nanocrystals is reported.
In the present work, the striations and diffraction characteristics of the β phase of Ti-5553 alloy are thoroughly investigated.
The theoretical limitations and experimental challenges of X-ray angular correlation analysis methods are investigated. Using a combination of simulated data and measurements on challenging meso-cluster samples, prepared using lithography and self-assembly, the primary experimental challenges are explored. Background scattering, data masking and inter-object interference are identified as primary challenges. Strategies to overcome correlation artifacts are presented.
A quantitative phase analysis technique, which can derive weight fractions of individual crystalline phases from their observed integrated intensities and chemical composition data, has been applied to the quantification of materials whose chemical compositions are unknown or indefinite because of substitutional replacements, nonstoichiometric composition etc.
An advanced three-dimensional reciprocal-space mapping by reflection high-energy electron diffraction (RHEED), grazing-incidence X-ray diffraction (GIXD) and grazing-incidence small-angle X-ray scattering (GISAXS)has been applied to study arrays of magnetically ordered Ni islands grown epitaxially on the surface of differently oriented CaF2/Si layers.
A versatile procedure to calculate two-dimensional scattering patterns from oriented systems is presented.
This study reports an angular diffraction peak shift that scales linearly with the neutron beam path length traveled through a diffracting sample. A hypothesis for the origin of this shift is presented, based upon non-ideal focusing of the neutron monochromator in combination with changes to the wavelength distribution reaching the detector due to factors such as attenuation.
The bulk and surface textures of recrystallized straight-rolled α-uranium foils are established by both neutron and X-ray diffraction and discussed relative to the existing literature on α-uranium processing textures.
A fundamental description of the instrument resolution file is elaborated for the angular- and wavelength-dispersive cases of Rietveld refinement, exemplified for the POWGEN instrument. It is shown how to refine the necessary profile function parameters from a dataset measured on a diamond reference sample. The analysis is performed in a two-dimensional refinement space based on the convenient variables d and d⊥.
An X-ray scattering study of intercalated water in multi-layered graphene oxide paper during hydration and thermal dehydration processes is presented. The evolution of X-ray scattering features depending on the presence and the type of intercalated water is discussed with the help of a simple structural model.
Rank aggregation is used as an alternative approach for merging serial electron crystallography data. The described algorithm avoids the problem of scaling entirely and is insensitive to errors in the reflection intensities.
The article considers supercell symmetry and Wyckoff position splittings for the description of defective crystals.
By simultaneously measuring changes in energy and reflection angle of Laue spots with respect to a reference position, it is possible to measure all lattice parameters of a unit cell and calculate the full strain/stress tensors in a single-shot experiment with high spatial resolution.
In situ protein crystallization on highly X-ray transparent nanomembranes is described and an application is outlined for the collection of diffraction data at X-ray free-electron lasers.
The scattering properties of surface fractals are studied by means of their decomposition into a sum of mass fractals.
The design and application of an enclosed micro-device for generating laser-induced semi-stationary states in light-sensitive microcrystals are described. The setup is suitable for time-resolved serial crystallography at synchrotrons and X-ray free-electron lasers.
The local mechanical behavior of a bulk stainless steel crystal is measured directly, at the micrometre scale, by combining total strain measurements with elastic strain measurements.
teaching and education
SLADS is a parallel code for direct simulations of single-shot X-ray scattering of large anisotropic dense nanoparticle systems of arbitrary species and atomic configurations. Particles can be of arbitrary shapes and dispersities, and interactions between particles are considered.
The Powder Calibration and Processing packages implemented in DAWN 2 provide an automated diffraction-geometry calibration and data processing environment for two-dimensional diffraction experiments. The customizable processing chains permit the execution of data processing steps to convert raw two-dimensional data into meaningful data and diffractograms. The provenance of the processed data is maintained, which guarantees reproducibility and transparency of the data treatment.
A simple, free and open-source program is presented that allows processing of large diffraction data files recorded with the Bruker D8 diffractometer. It can be downloaded from https://aboulle.github.io/DxTools/.
A new data acquisition system is proposed for in situ single-crystal diffraction with a pixel area detector under an alternating electric field.
addenda and errata
One imprecise and one incomplete statement in the article by Nespolo [J. Appl. Cryst. (2015), 48, 1290–1298] are corrected.