August 2020 issue
The crystallography and mechanism of the early stages of the formation of cubic primitive γ′-Fe4N in single-crystal α-Fe whiskers during gaseous nitriding were investigated by electron microscopy and electron backscatter diffraction. The α–γ′ phase transformation could be observed under simplified conditions owing to the lack of geometric constraints for the transformation.
White beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.
A detailed theoretical and experimental comparison of dark-field electron holography and high-resolution X-ray diffraction is performed. Both techniques are applied to measure elastic strain in an array of metal–oxide–semiconductor field-effect transistors (MOSFETs) and the role of the geometric phase is emphasized.
A growth model of hematite crystals derived from magnetite–hematite phase transformation is determined from a new orientation condition.
This paper reports the application of the moment series expansion of the characteristic function of the distribution associated with the geometric part of the structure factor to model phason disorder in the structure refinement of the decagonal quasicrystal AlCuRh. The main result is that combining a new approach to phasons with the standard Gaussian Debye–Waller formula gives better refinement results and a finer atomistic model of quasicrystals, based on the decagonal AlCuRh system.
A laboratory Laue transmission setup has been developed to evaluate single-crystal quality in extended specimens. The method combines a compact high-energy setup, a general indexing algorithm and a forward model. Orientation mapping and parasite grain detection can be achieved by scanning a part in the plane perpendicular to the beam.
Simultaneous wavefront metrology and sample projection imaging with multi-layer Laue lenses using the ptychographic X-ray speckle tracking technique is described. Results from three experiments are presented.
Understanding the wavefront of ultra-bright and ultra-short pulses of X-ray free-electron lasers is both important and challenging. A method based on ptychography that can retrieve full high-resolution complex-valued wave functions of individual pulses is presented.
The effect of 2,4-dinitrophenol dye doping on tristhioureazinc(II) sulfate bulk single crystals has been studied with regard to their structural, mechanical, thermal, electrical and optical properties for nonlinear optical device applications.
A new synchrotron-compatible furnace for simulating the environment inside an optical floating zone furnace is described. It is shown that temperature profiles within heated rods can be determined from in situ synchrotron diffraction data, and that these measured profiles can be reproduced with a four-component heat-transfer model.
Seven small-angle scattering structure factors are presented, including one novel structure factor. It is demonstrated how the structure factors are best applied to describe aggregation processes or to take scattering from undesired aggregates into account.
Synchrotron X-ray diffraction measurements performed on Mg samples allowed the retrieval of preferred configurations of grain boundary interfaces through the observation of weak diffraction peaks located between fundamental reflections. Kinematical simulations verifying possible interface structures established the correspondence of the non-bulk peaks to grain boundary interfaces that may be less energetic than the usually investigated twin-plane symmetric conditions.
The effect of applied stress state and β crystal orientation on available work from β-to-α′′ martensite formation in metastable β Ti alloys is analysed. Predictions based on an available work criterion show a strong effect of stress and crystal orientation, and consequences for forming processes and typical β textures are discussed.
Real-time X-ray scattering reveals the growth of 3D correlated quantum dots in situ during ion beam deposition.
A new single-crystal X-ray diffraction method and data analysis framework have been developed and implemented for the separation of intrinsic and domain-wall-motion contributions to the piezoelectric effect in functional ferroelectric materials. The technique is applied for the elucidation of the mechanism of piezoelectricity in a single crystal of the ferroelectric PbZr0.65Ti0.35O3.
A viscous-medium-based crystal support in a sample holder has been developed for fixed-target serial crystallography.
A modified dictionary indexing method is proposed to resolve pseudosymmetry in electron backscatter diffraction. The method is applied to simulated and experimental data sets of tetragonal ZrO2 and demonstrated to correctly resolve pseudosymmetry.
A novel approach to parafocusing X-ray diffraction with an annular incident beam is demonstrated. Proof of principle is achieved via a theoretical approach, simulations and experiments, demonstrating significantly higher intensity scattering when compared with conventional Bragg–Brentano geometries, but without the need for flat-specimen approximations.
AlN single crystals grown by physical vapor transport have been analyzed by X-ray methods to evaluate dislocation types, densities and spatial distribution within the crystal. Potential changes of the AlN crystal quality during growth, both within the axial growth direction and within lateral expansion areas, have been investigated.
Complex modeling is used for local and average atomic structure, nanostructure and microstructure quantification of an Au0.25Cu0.75 alloy. This approach is generalizable and should be extensible to other disordered systems, allowing for quantification of localized structure deviations.
teaching and education
Algebraic, vector and matrix methods (including metric matrices) for the calculation of molecular bond lengths, bond angles and bond torsion angles in crystal or direct space, using fractional or Cartesian coordinates, are described. Two live Excel implementations of the methods are provided, in which the reader may introduce their own coordinate data for automatic calculation.
A software package is described for grazing-incidence wide-angle X-ray scattering geared towards weakly ordered materials, with functionality including scattering intensity normalization/uncertainty estimation, scattering pattern indexing and refractive shift correction.
EDDIDAT is a program that provides a graphical user interface for the evaluation of energy-dispersive X-ray diffraction data with the focus on depth-resolved residual stress analysis.
Chirok is a new tool for a post-refinement analysis of absolute structures. It is based on the fit of a statistical distribution of Parsons quotients with various peak functions.
X-Seed is still in use after two decades, during which time a number of enhancements have been implemented. It mainly serves as a graphical user interface for SHELX and POV-Ray, and facilitates exploration of crystal packing.
SAS-cam is an automated data analysis pipeline, developed to meet the high-throughput operation requirements of synchrotron-facility-based small-angle scattering.
A program is described that enables the energetics of crystal packing to be analysed quickly and easily through a user interface, using Pixel, Python scripts and the widely known visualizer Mercury.
A feasibility study is carried out of an autoclave chamber for in situ X-ray diffraction experiments under hydrothermal conditions. Quartz dissolution and tobermorite formation are monitored on conventional laboratory X-ray diffractometers.