X-ray Laue Diffraction Research Articles

Sublimation growth of bulk 3C-SiC using 3C-SiC-on-Si (1 0 0) seeding layers

We have developed a transfer process of 3C-SiC-on-Si (100) seeding layers grown by chemical vapor deposition onto a poly- or single-crystalline SiC carrier. Applying subsequent sublimation growth of SiC in [100] direction resulting in large area crystals (up to ≈11cm2) with a thickness of up to approximately 850μm. Raman spectroscopy, Laue X-ray diffraction and electron-backscattering-diffraction revealed a high material quality in terms of single-crystallinity without secondary polytype inclusions, antiphase boundaries or double positioning grain boundaries. Defects in the bulk grown 3C-SiC, like protrusions with surrounding stressed areas, stem from the epitaxial seeding layer. The presented concept using 3C-SiC-on-Si seeding layers reveals a path for the growth of bulk 3C-SiC crystals.

Micro-beam Laue alignment of multi-reflection Bragg coherent diffraction imaging measurements.

Multi-reflection Bragg coherent diffraction imaging has the potential to allow three-dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here a different approach is demonstrated, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focused ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples.

Boundary migration in a 3D deformed microstructure inside an opaque sample

How boundaries surrounding recrystallization grains migrate through the 3D network of dislocation boundaries in deformed crystalline materials is unknown and critical for the resulting recrystallized crystalline materials. Using X-ray Laue diffraction microscopy, we show for the first time the migration pattern of a typical recrystallization boundary through a well-characterized deformation matrix. The data provide a unique possibility to investigate effects of both boundary misorientation and plane normal on the migration, information which cannot be accessed with any other techniques. The results show that neither of these two parameters can explain the observed migration behavior. Instead we suggest that the subdivision of the deformed microstructure ahead of the boundary plays the dominant role. The present experimental observations challenge the assumptions of existing recrystallization theories, and set the stage for determination of mobilities of recrystallization boundaries.

Single-shot full strain tensor determination with microbeam X-ray Laue diffraction and a two-dimensional energy-dispersive detector.

The full strain and stress tensor determination in a triaxially stressed single crystal using X-ray diffraction requires a series of lattice spacing measurements at different crystal orientations. This can be achieved using a tunable X-ray source. This article reports on a novel experimental procedure for single-shot full strain tensor determination using polychromatic synchrotron radiation with an energy range from 5 to 23 keV. Microbeam X-ray Laue diffraction patterns were collected from a copper micro-bending beam along the central axis (centroid of the cross section). Taking advantage of a two-dimensional energy-dispersive X-ray detector (pnCCD), the position and energy of the collected Laue spots were measured for multiple positions on the sample, allowing the measurement of variations in the local microstructure. At the same time, both the deviatoric and hydrostatic components of the elastic strain and stress tensors were calculated.

Anisotropy study on thermionic emission and magnetoresistivity of single crystal CeB6

Cerium hexaboride (CeB6) as a heavy fermion compound displays a number of interesting low-temperature physical properties such as dense Kondo behavior and a complex magnetic phase diagram due to the interaction between itinerant and local electrons. Recently, the electron emission property of CeB6 has received much attention because it has potential applications in replacing the commercial LaB6 cathode and serving as new-generation thermal cathodes. In addition, by comparison with other metal cathodes, it also possesses some advantages, such as a low work function, low volatility, high brightness, thermal stability and high mechanical strength. However, so far the thermionic emission properties of CeB6 single crystal surfaces except for the (100) surfaces have been rarely reported. Whether the different crystal surfaces of CeB6 contribute to the various interesting emission properties is main research purpose of the present work. In this paper, the (110), (111), (210) and (310) crystal surfaces of single crystal CeB6 are determined by the X-ray Laue diffraction method, and their thermionic emission current densities are measured at different temperatures and applied voltages. As a result, the maximum emission current densities of the (110), (111), (210) and (310) crystal surfaces at 1873 K are 38.4, 11.54, 50.4 and 20.8 A/cm2, respectively. When their cathode temperatures are all 1773 K, their maximum emission current densities are 15.2, 5.43, 28.0 and 11.44 A/cm2. In addition, when the cathode temperature decreases to 1673 K, their maximum emission current densities are 4.24, 0.9, 6.2 and 2.43 A/cm2. It means that the thermionic emissions are strongly anisotropic for the different crystal surfaces. In general, the maximum emission current density of (100) crystal surface of LaB6 single crystal is about 10 A/cm2 at 1700 K. By comparing the emission current density of CeB6 single crystal at 1773 K with that of LaB6 at 1700 K, it is found that the emission properties of (210) crystal surface are maybe close to those of LaB6. The work function values of the (110), (111), (210) crystal surfaces calculated by the Richardson-Dushman formula are 2.64, 2.71 and 2.40 eV, respectively. Among these, the (210) crystal surface possesses the smallest value of the work function, which is hopeful for being used as an electron source of scanning electron microscopy. Zero-field magnetoresistivity measurments confirm the transition temperatures of TQ=3.3 K and TN=2.4 K. Field-angle dependent magnetoresistivity measurments show that the electrical resistivity varies between 69 μupΩ·cm and 73 μupΩ·cm when the crystal rotates from the[001] to the[011] direction. This indicates that the electrical resistivity in a magnetic field is also anisotropic.

On the fracture of multi-crystalline silicon wafer

This work focuses on the fracture behavior of multi-crystalline silicon in 4-point bending tests. The objective is to investigate the crack path as well as the effect of the grain boundary on the crack propagation. Thin specimens that contain the same grains have been tested under identical loading in order to assess the consistency of the fracture process. Fractography analysis has been carried out with a confocal microscope to describe the crack propagation within grains and at grain boundaries. The fracture paths have been also compared to X-FEM numerical simulations, and a very good agreement was found. Fractographies have been used to identify the cleavage planes in locations where surface instabilities are observed, and to reveal how grain boundaries are crossed. Laue x-ray diffraction analysis has been carried out to measure the grain orientations and further identify the cleavage planes in the areas far from instabilities and grain boundaries. It is observed that the fracture of multi-crystalline silicon is completely determinist, i.e. the same crack path for twin silicon plates, with the crack propagating mainly on the crystallographic plane and eventually on . The misorientation across the grain boundary can drive the crack away from the lowest surface energy plane. Another interesting observation is that the grain boundary slows down or stops shortly the crack propagation.

MultiLaue: A Technique to Extract d-spacings from Laue XRD

doi:10.1017/S1431927616009764 Microsc. Microanal. 22 (Suppl 3), 2016 © Microscopy Society of America 2016 MultiLaue: A Technique to Extract d-spacings from Laue XRD Zack Gainsforth 1 , Matthew A. Marcus 2 , Nobumichi Tamura 2 and Andrew J. Westphal 1 University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, 91020, USA Lawrence Berkeley Laboratory, Advanced Light Source, Berkeley, CA, 91020, USA Broad spectrum X-ray Diffraction (XRD) is named Laue after Max von Laue, and is the original XRD technique [1]. Today, monochromatic XRD is more common because Bragg's equation allows determination of d-spacings where Laue does not. Laue still remains in use for single crystal systems because it can be used to make very accurate unit cell determinations as well as for strain and orientation mapping. A Laue technique which could provide unambiguous determination of lattice spacings, a la Bragg's equation would be a huge leap forward, especially for multiphase samples such as meteorites, interplanetary dust particles and some geological specimens. We introduce a new technique we call multiLaue which allows such determination. First an unfiltered Laue pattern is acquired. Then a filter is inserted between the radiation source and the sample – in this case a 100 um thick fused silica wafer – and a new Laue pattern is acquired. A shield protects the detector from radiation scattered off the filter. Low energy X-rays are more strongly absorbed by the filter than high energy X-rays so reflections excited by low energies are more attenuated relative to those excited by high energies. We developed a computer model simulating the process, and use it to quantitatively determine the X-ray energy exciting a reflection based on the reduction of intensity across a set of three filters (100, 200 and 300 micron fused silica). We tested multiLaue on a Si chip on beamline 12.3.2 at the Advanced Light Source synchrotron. The unfiltered pattern is shown in Figure 1. We analyzed 32 reflections (Table 1) and computed best fit energies. These are compared with energies based on indexation via the XMAS software [2]. The best fit energies matched well between 11 and 23 keV, with a mean relative error of 1.9% and a standard deviation of the error of 1.4%. This means we can compute d-spacings with an accuracy of 21 keV have large errors. Reflections < 11 keV have a harmonic contribution from the spectrum above 21 keV and also show large errors. Therefore, accurate characterization of the radiation source, and optics is crucially important to achieving high accuracy quantification.

Dynamic deformation and fracture of single crystal silicon: Fracture modes, damage laws, and anisotropy

Impact fracture of single-crystal Si is critical to long-term reliability of electronic devices and solar cells for its wide use as components or substrates in semiconductor industry. Single-crystal Si is loaded along two different crystallographic directions with a split Hopkinson pressure bar integrated with an in situ x-ray imaging and diffraction system. Bulk stress histories are measured, simultaneously with x-ray phase contrast imaging (XPCI) and Laue diffraction. Damage evolution is quantified with grayscale maps from XPCI. Single-crystal Si exhibits pronounced anisotropy in fracture modes, and thus fracture strengths and damage evolution. For loading along [11¯ 0] and viewing along [001], (1¯1¯0)[11¯ 0] cleavage is activated and induces horizontal primary cracks followed by perpendicular wing cracks. However, for loading along [011¯] and viewing along [111], random nucleation and growth of shear and tensile-splitting crack networks lead to catastrophic failure of materials with no cleavage. The primary-wing crack mode leads to a lower characteristic fracture strength due to predamage, but a more concentrated strength distribution, i.e., a higher Weibull modulus, compared to the second loading case. Moreover, the sequential primary cracking, wing cracking and wing-crack coalescence processes result in a gradual increase of damage with time, deviating from theoretical predictions. Particle size and aspect ratios of fragments are discussed with postmortem fragment analysis, which verifies fracture modes observed in XPCI.

Following dislocation patterning during fatigue

Precursors of failure are dislocation mechanisms at the nanoscale and dislocation organization at the mesoscale responsible for long-range internal stresses and lattice rotation. Detailed information on the link between both scales is missing, computationally and experimentally. Here we present a method based on x-ray Laue diffraction scanning providing time and sub-micron spatially resolved evolution of geometrical necessary dislocations in volumes that are similar to what advanced computational models can achieve. The approach is used to follow dislocation patterning during accumulation of fatigue cycles using a newly developed miniaturized shear device. Performed on Cu during cyclic shear, it reveals early dislocation patterning influenced by pre-existing dislocation structures. The quantitative information on non-homogeneous structure formation and its evolution corresponds to the need for synergies with continuum dislocation plasticity simulations of fatigue or any other type of plastic deformation.

Dynamic crystal rotation resolved by high-speed synchrotron X-ray Laue diffraction.

Dynamic compression experiments are performed on single-crystal Si under split Hopkinson pressure bar loading, together with simultaneous high-speed (250-350 ns resolution) synchrotron X-ray Laue diffraction and phase-contrast imaging. A methodology is presented which determines crystal rotation parameters, i.e. instantaneous rotation axes and angles, from two unindexed Laue diffraction spots. Two-dimensional translation is obtained from dynamic imaging by a single camera. High-speed motion of crystals, including translation and rotation, can be tracked in real time via simultaneous imaging and diffraction.

Fast GPU-based absolute intensity determination for energy-dispersive X-ray Laue diffraction

This paper presents a novel method for fast determination of absolute intensities in the sites of Laue spots generated by a tetragonal hen egg-white lysozyme crystal after exposure to white synchrotron radiation during an energy-dispersive X-ray Laue diffraction experiment. The Laue spots are taken by means of an energy-dispersive X-ray 2D pnCCD detector. Current pnCCD detectors have a spatial resolution of 384 × 384 pixels of size 75 × 75 μm2 each and operate at a maximum of 400 Hz. Future devices are going to have higher spatial resolution and frame rates.The proposed method runs on a computer equipped with multiple Graphics Processing Units (GPUs) which provide fast and parallel processing capabilities. Accordingly, our GPU-based algorithm exploits these capabilities to further analyse the Laue spots of the sample. The main contribution of the paper is therefore an alternative algorithm for determining absolute intensities of Laue spots which are themselves computed from a sequence of pnCCD frames. Moreover, a new method for integrating spectral peak intensities and improved background correction, a different way of calculating mean count rate of the background signal and also a new method for n-dimensional Poisson fitting are presented.We present a comparison of the quality of results from the GPU-based algorithm with the quality of results from a prior (base) algorithm running on CPU. This comparison shows that our algorithm is able to produce results with at least the same quality as the base algorithm. Furthermore, the GPU-based algorithm is able to speed up one of the most time-consuming parts of the base algorithm, which is n-dimensional Poisson fitting, by a factor of more than 3. Also, the entire procedure of extracting Laue spots' positions, energies and absolute intensities from a raw dataset of pnCCD frames is accelerated by a factor of more than 3.

Macroscopically Aligned Graphite Films Prepared from Iodine-Doped Stretchable Polyacetylene Films Using Morphology-Retaining Carbonization.

We prepared graphite films using typical Shirakawa-type and stretchable polyacetylene (PA) films as precursors through a morphology-retaining carbonization. A macroscopically aligned PA film was prepared from the drawable PA film using a mechanical-stretching procedure. The degree of orientation of the aligned PA film was evaluated by measuring polarized infrared absorption spectra and an azimuthal-angle profile of a Laue X-ray diffraction (XRD) pattern. The carbonization was performed from the iodine-doped PA films as precursors at 800 °C. The carbon films were subsequently graphitized at 1400-3000 °C, yielding graphite films with almost the same surface morphology as that of the original PA films and that of the carbon films as precursors. The typical PA film graphitized at 2600 °C exhibited tensile strengths of up to 224 MPa, moduli of up to 10 GPa, and an average electrical conductivity of 2.5 × 10(2) S/cm. In contrast, the graphite film prepared from the stretched PA film presented a Laue XRD pattern in which graphitic crystal structures are aligned parallel to the direction of stretching of the PA film. The anisotropic graphite film showed an enhanced conductivity of up to 1.5 × 10(3) S/cm along the stretching direction. We demonstrated that an iodine-doped PA film is a highly efficient carbon source for producing graphite films with good mechanical and electrical properties. The total yield of a graphite film is as high as 61-74% at up to 3000 °C, which is considerably higher than that of polyacrylonitrile-based carbon fiber and polyimide-based graphite film.

High pressure Laue diffraction and its application to study microstructural changes during the α → β phase transition in Si.

An approach using polychromatic x-ray Laue diffraction is described for studying pressure induced microstructural changes of materials under pressure. The advantages of this approach with respect to application of monochromatic x-ray diffraction and other techniques are discussed. Experiments to demonstrate the applications of the method have been performed on the α → β phase transition in Si at high pressures using a diamond anvil cell. We present the characterization of microstructures across the α-β phase transition, such as morphology of both the parent and product phases, relative orientation of single-crystals, and deviatoric strains. Subtle inhomogeneous strain of the single-crystal sample caused by lattice rotations becomes detectable with the approach.

A laboratory-based Laue X-ray diffraction system for enhanced imaging range and surface grain mapping.

Although CCD X-ray detectors can be faster to use, their large-area versions can be much more expensive than similarly sized photographic plate detectors. When indexing X-ray diffraction patterns, large-area detectors can prove very advantageous as they provide more spots, which makes fitting an orientation easier. On the other hand, when looking for single crystals in a polycrystalline sample, the speed of CCD detectors is more useful. A new setup is described here which overcomes some of the limitations of limited-range CCD detectors to make them more useful for indexing, whilst at the same time making it much quicker to find single crystals within a larger polycrystalline structure. This was done by combining a CCD detector with a six-axis goniometer, allowing the compilation of images from different angles into a wide-angled image. Automated scans along the sample were coupled with image processing techniques to produce grain maps, which can then be used to provide a strategy to extract single crystals from a polycrystal.

Fast GPU-based spot extraction for energy-dispersive X-ray Laue diffraction

This paper describes a novel method for fast online analysis of X-ray Laue spots taken by means of an energy-dispersive X-ray 2D detector. Current pnCCD detectors typically operate at some 100 Hz (up to a maximum of 400 Hz) and have a resolution of 384 × 384 pixels, future devices head for even higher pixel counts and frame rates.The proposed online data analysis is based on a computer utilizing multiple Graphics Processing Units (GPUs), which allow for fast and parallel data processing. Our multi-GPU based algorithm is compliant with the rules of stream-based data processing, for which GPUs are optimized. The paper's main contribution is therefore an alternative algorithm for the determination of spot positions and energies over the full sequence of pnCCD data frames. Furthermore, an improved background suppression algorithm is presented.The resulting system is able to process data at the maximum acquisition rate of 400 Hz. We present a detailed analysis of the spot positions and energies deduced from a prior (single-core) CPU-based and the novel GPU-based data processing, showing that the parallel computed results using the GPU implementation are at least of the same quality as prior CPU-based results. Furthermore, the GPU-based algorithm is able to speed up the data processing by a factor of 7 (in comparison to single-core CPU-based algorithm) which effectively makes the detector system more suitable for online data processing.

X-ray Laue diffraction with allowance for two-dimensional curvature of the wavefront: The concept a locally plane wave

Symmetrical Laue diffraction in a perfect crystal with a plane entance surface is considered. The two dimensional curvature of the wave front of the incident beam is taken into account. Using the corresponding Green function, a general expression for the amplitude of diffracted wave in the crystal is presented. Based on this expression, the concept of a locally plane wave is analyzed taking into account two-dimensional curvature of the wave front. This concept is used for obtaining the rocking curves depending on the angles of deviation from the chosen exact Bragg direction in both the diffraction plane and in perpendicular direction. The obtained result is compared with the result of the standard dynamical diffraction theory.

Focusing of hard X-ray beams in quartz crystal under the temperature gradient

The research of the focusing and defocusing of the diffracted X-rays with different wave fronts in crystals under the influences of the temperature gradient and the ultrasonic vibrations is given in the works [1,2]. This work is dedicated experimentally investigation of Laue diffraction of the hard X-rays in quartz single crystals under the influence of the temperature gradient. It is shown that the reflected beams under the influence of the temperature gradient are focused. When the vector of the temperature gradient is anti parallel to the diffraction vector, in accordance to the increasing value of the temperature gradient the focus point continuously approaches the crystal. When the vector of the temperature gradient is parallel to the diffraction vector, in accordance with the increasing value of the temperature gradient the focus point continuously distances itself from the crystal, and at a certain value of the temperature gradient it becomes a plane wave. Parallel to the further increasing of the temperature gradient we see an imaginary focus, which continuously approaches the entry surface of the crystal. It is shown that by using a thicker single crystal it is possible to focus and pump a larger angular and spectral width of X-rays in the direction of diffraction.

LEED and TEM analysis of Bismuth Telluride

Bismuth Telluride has recently been identified as a 3D-topological insulator [1] as well as Graphene [2]. Topological insulators are a quite recent discovered quantum mechanics characteristic of materials where essentially the surface band structure is completely different from the bulk. Bismuth Telluride, for example has its semi-metallic behavior changed into a conducting one. However it has been well known, as an excellent thermoelectric material [3]; with relatively high thermoelectric coefficients at room temperature. Bismuth Telluride is a relatively easy material to obtain and different compositions are being studied both as bulk material and as thin films. Crystals of Bi2Te3 were Bridgman grown in a sealed quartz ampoule in a directional resistance oven at a temperature of 600oC. Conventional X-ray Laue diffraction showed patterns compatible with a single crystal along the sample except for the starting point, which was discarded. Transmission and Scanning Electron Microscopy and Low Energy Electron Diffraction (LEED) were performed. The grown crystals were cleaved and small parts were crushed on a mortar with ethanol and deposited onto a holey carbon grid. Also thin slices were cut in an ultramicrotome (Leica UC6) with a diamond knife and deposited onto a holey carbon coated grid. TEM measurements showed the presence of grains on both samples with a very small deviation from the observed crystallographic axis (0001). However LEED measurements showed only a single crystalline pattern. Electron backscatter diffraction (EBSD) studies showed large granular areas with a extremely small angular variation between the grains. It is still unclear if those differences are real or due to sample preparation artifacts and effort is being put into analyzing exactly the same piece with all the different techniques.

Crystal growth and mechanical characterization of ZrMo2O8

We report a fluxing technique for ZrMo2O8 single crystal growth. The volatility of MoO3 coupled with the limited temperature range of its stability with the liquid phase makes the single crystal growth of ZrMo2O8 a formidable challenge. Single crystal growth of ZrMo2O8 was carried out in a horizontal tubular furnace using a platinum boat and utilizing Li2MoO4 as a fluxing agent. The synthesized faceted crystals were up to 3mm along the maximum dimension. Laue and single crystal X-ray diffraction confirmed the monoclinic crystal structure having a space group C 1 2/c 1 (S.G#15), and a single crystallographic domain within the crystals. Reduced elastic modulus and hardness were determined to be 108±4GPa and 6.4±0.2GPa respectively using nanoindentation. Appearance of additional peaks in Raman spectra of the indented region when compared with the fresh crystal indicated a possible pressure induced phase transformation during indentation.

Growth of single crystalline delafossite LaCuO2 by the travelling-solvent floating zone method

Single crystals of LaCuO2 have been grown for the first time using the travelling-solvent floating zone method. The crystal was grown in an Ar-atmosphere by reduction of La2Cu2O5, which was used as the feed rod composition for the growth. The grown crystal has been characterized with regard to phase purity and single crystallinity using powder X-ray diffraction, energy dispersive X-ray analysis, Laue diffraction and scanning electron microscopy.