Energy-dispersive Laue Diffraction Research Articles

In situ observations of single grain behavior during plastic deformation in polycrystalline Ni using energy dispersive Laue diffraction

Energy dispersive X-ray Laue diffraction is applied to investigate the deformation behavior of individual grains in a polycrystalline nickel wire under tensile loading. 38 Laue spots are identified in the Laue pattern which originate from 9 separate grains. The simultaneous measurements of the Laue spot's position and energy obtained by using a 2D energy dispersive detector, allows to track the evolution of the 9 grains through multiple stages of deformation. Angular and spectral elongation (streaking) of the Laue spots increases as tensile loading is increased and is attributed to macroscopic texture changed and strain due to defect accumulation. On the single grain level, a correlation between crystallographic orientation and strain is investigated. Moreover, spatially resolved anisotropic deformation within a single grain is measured to increase at the grain boundaries. Comparison of the grain specific responses allow for development of a deformation scenario for the whole specimen. The presented experiment demonstrates an alternative protocol for the investigation of deformation mechanisms in polycrystalline materials.

Energy-dispersive Laue diffraction by means of a pnCCD detector coupled to a CsI(Tl) scintillator using ultra-hard X-ray synchrotron radiation.

The lattice parameters and unit-cell orientation of an SrLaAlO4 crystal have been determined by means of energy-dispersive X-ray Laue diffraction (EDLD) using a pnCCD detector coupled to a columnar structure CsI(Tl) scintillator in the energy range between 40 and 130 keV. By exploiting the high quantum efficiency (QE) achieved by this combined detection system for hard X-rays, a large number of Bragg reflections could be recorded by the relatively small detector area, allowing accurate and fast determination of the lattice parameters and the moduli of the structure factors. The experiment was performed on the energy-dispersive diffraction (EDDI) beamline at the BESSY II synchrotron using a pnCCD detector with 128 × 128 pixels. Since the energies and positions of the Laue peaks can be recorded simultaneously by the pnCCD system, the tetragonal structure of the investigated specimen was determined without any prior information. The unit-cell parameters and the angles between the lattice vectors were evaluated with an accuracy of better than 0.7%, while the structure-factor moduli of the reflections were determined with a mean deviation of 2.5% relative to the theoretical values.

Energy-dispersive Laue experiments with X-ray tube and PILATUS detector: precise determination of lattice constants

A PILATUS detector in combination with a conventional sealed X-ray tube was used for the development of the energy-dispersive Laue diffraction technique, which can be applied for precise measurements of single-crystal lattice constants in transmission and reflection modes without moving the sample. Exploiting the ability of PILATUS detectors to suppress counting of X-ray photons below a certain energy threshold allows one to recover the wavelength of diffracted Bragg reflections, reconstruct the three-dimensional reciprocal-space pattern, index X-ray diffraction peaks, and find the orientation and lattice parameters of the crystal without any a priori information about the sample. By making some geometrical assumptions and using a set of fast in situ calibration procedures, it is possible to simultaneously refine lattice constants and hardware correction factors, which simplifies the sample preparation and measurement strategies. Several samples [silicon, quartz, fluorite (CaF2), o′-Al13Co4 quasicrystal approximant, Laves (MgZn2) and Bergman (Mg32(Al,Zn)49) phases] were studied with the developed technique, and 0.01 Å and 0.1° precisions were routinely reached for lattice vector lengths and angles, respectively. The use of the developed methods is only limited by the energy resolution of the PILATUS detector, where lattice vectors with >27 Å length cannot be reliably resolved.

EDLD-Tool: A real-time GPU-based tool to stream and analyze energy-dispersive Laue diffraction of BIG Data sets collected by a pnCCD

Energy-dispersive Laue diffraction (EDLD) is a tool for the characterization of single-crystalline and polycrystalline materials. Using a two-dimensional energy-dispersive detector, both the angular positions and the diffracting energies of the Laue spots can be analysed without additional information, allowing for fast indexing, determination of the crystal structure and the respective lattice parameters. Running the detector at ≈ 400 Hz, a typical data set (≈ 10 min) taken by the single photon counting mode has a size of ten Gigabytes. Up to now, problems such as data transfer, data storage, data reduction and on time data analysis are drawbacks for wider application of this technique. A fast and effective algorithm for processing of these BIG Data is required to overcome the drawbacks and to allow for quality assessment of the running experiment in real time. This paper presents a GPU based tool for energy-dispersive Laue diffraction (EDLD) experiments, named “EDLD-Tool”, providing the optimization of geometric parameters of the experiment, auto-indexation, online steering, error detection and determination of all crystal parameters considering pnCCD data taken from a single crystal. This tool is exploiting parallel computing technology of the GPU and makes use of many scientific, high performance libraries (i.e. OpenCV, Root-Cern, Eigen and others). As a result, the developed tool allows for data processing in the time frame of few seconds compared to the previous analysis system which requires few hours to process the same amount of data.

Photon Energy Becomes the Third Dimension in Crystallographic Texture Analysis.

Conventional analysis of the preferred orientation of crystallites (crystallographic texture) involves X-ray diffraction with area detectors and 2D data output. True 3D, spatially resolved information requires sample rotation in the beam, thus changing the probed volume, which introduces signal smearing and precludes the scanning of complex structures. This obstacle has been overcome by energy-dispersive Laue diffraction. A method has been devised to reach a large portion of reciprocal space and translate the X-ray photon energy into the missing third dimension of space. Carbon fibers and lobster exoskeleton as examples of biomineralized tissue have been analyzed. The major potential of this method lies in its "one-shot" nature and the direct 3D information requiring no previous knowledge of the sample. It allows the texture of large samples with complex substructures to be scanned and opens up the conceptual possibility of following texture changes in situ, for example, during crystallization.

High Speed, High Resolution Imaging Spectrometers Based on pnCCDs for XRF and XRD Applications

For many years pnCCDs have been well known as X-ray detectors for spectroscopic imaging in many fields of science: X-Ray Fluorescence analysis (XRF), X-ray Diffraction (XRD) with light sources in large accelerator facilities as well as with laboratory light sources or with X-rays from celestial sources in X-ray astronomy. A brief introduction in GEXRF (Grazing Emission XRF) measurements with a laboratory laser produced plasma source will be given, PIXE (Particle Induced X-ray Emission) measurements and D2XRF (Double Dispersive X-Ray Fluorescence) and Slicing experiments with pnCCDs coupled to polycapillary optics performed at the BESSY synchrotron will be shown. Energy-dispersive Laue diffraction with ultra-hard X-rays for the analysis of defects in metals will conclude the overview of spectroscopic X-ray imaging measurements in the field of structure and dynamics of matter.

Application of a pnCCD for energy-dispersive Laue diffraction with ultra-hard X-rays

In this work the spectroscopic performance of a pnCCD detector in the ultra-hard energy range between 40 and 140 keV is tested by means of an energy-dispersive Laue diffraction experiment on a GaAs crystal. About 100 Bragg peaks were collected in a single-shot exposure of the arbitrarily oriented sample to white synchrotron radiation provided by a wiggler at BESSY II and resolved in a large reciprocal-space volume. The positions and energies of individual Laue spots could be determined with a spatial accuracy of less than one pixel and a relative energy resolution better than 1%. In this way the unit-cell parameters of GaAs were extracted with an accuracy of 0.5%, allowing for a complete indexing of the recorded Laue pattern. Despite the low quantum efficiency of the pnCCD (below 7%), experimental structure factors could be obtained from the three-dimensional data sets, taking into account photoelectric absorption as well as Compton scattering processes inside the detector. The agreement between measured and theoretical kinematical structure factors calculated from the known crystal structure is of the order of 10%. The results of this experiment demonstrate the potential of pnCCD detectors for applications in X-ray structure analysis using the complete energy spectrum of synchrotron radiation.

Application of a pnCCD for energy-dispersive Laue diffraction with ultra-hard X-rays

Application of a pnCCD for energy-dispersive Laue diffraction with ultra-hard X-rays

In-house energy resolved Laue XRD measurements with a Pilatus detector

The use of 2D position and energy sensitive hybrid pixel Pilatus detectors allows performing energy-dispersive analysis of Bragg reflections [1]. This significantly improves the classical Laue experiments enabling the unique determination of the crystal lattice and resolving the higher order harmonics. It allows quantitative crystal structure determination using the Laue method without having any priory information about the crystal [2]. Such energy-dispersive Laue diffraction (EDLD) experiments can be performed with a white X-ray beam either from a synchrotron source or from conventional X-ray tubes. The second approach looks less profitable due to its lower irradiation intensity, but this can be compensated considering the better control of white beam spectra by applying different voltage/current settings during the tube operation. Thus, one can efficiently combine the primary beam and XRD measurements using the same Pilatus detector. This allows the implementation of the energy resolved (color Laue) method for any conventional XRD diffractometer equipped with a Pilatus detection system. In the present work EDLD experiments with a conventional X-ray tube were combined with corresponding primary beam measurements using a 300K Pilatus detector tuned for operation within an energy range of 4-25 keV at energy resolution <0.12 keV. Such a combination simplifies several data correction procedures (the spectral intensity distribution, the sample absorption etc.) significantly. Following our developed intensity correction protocols the structure refinement of a reference quartz sample could be achieved with R-factor <0.10. Possible applications of this method (e.g. quantitative XRD studies with stationary crystals) and the details for its further development will be discussed.

Energy-dispersive Laue diffraction by means of a frame-store pnCCD

A frame-store pn-junction CCD detector was applied to the energy-dispersive X-ray Laue diffraction study of a γ-LiAlO2crystal with white synchrotron radiation. Exploiting the simultaneous spatial and energy resolution of the detector the crystallographic unit cell of γ-LiAlO2could be determined without anya prioriinformation about the sample. The potential for application in X-ray structure analysis is tested by comparing experimental structure factors taken under a single exposure with those calculated from the known crystal structure. After correcting the measured spot intensities by angular and energy-dependent parameters, the agreement between experimental and theoretical kinematical structure factors is better than 10%.