Two-dimensional Area Detector Research Articles

Exploring the impact of incoherent Compton scattering on X-ray pair distribution function analysis of disordered materials

X-ray atomic pair distribution function (XPDF) measurements using a two-dimensional area detector have been of great value in studying atomic structures of materials with varying degrees of disorder. However, an area detector does not have energy resolution. Thus, incoherent inelastic Compton scattering and fluorescence are not discriminated, contaminating coherent elastic scattering. This paper investigates the effects of random noise from incoherent scattering on XPDF analysis. To conduct the study, the elastic scattering, Compton scattering and fluorescence of In0.33Ga0.67As alloy were separately measured using an intrinsic Ge solid-state detector with energy resolution. It is found that the addition of Compton scattering with a noise-to-signal ratio of about 0.8% results in the smearing of diffuse scattering in the high-Q region. Moreover, adding extra noise from fluorescence increases the smearing, overwhelming the diffuse scattering. Additionally, simulated data of elastic and Compton scattering on ferroelectric Ba(Ti0.8Zr0.2)O3 were used to investigate the evolution of noise fluctuation and its effects on the XPDF as a function of total intensity.

Initial Growth Behavior in Catalyst-Free-Grown Vertical ZnO Nanorods on c-Al2O3, as Observed Using Synchrotron Radiation X-ray Scattering

In this study, synchrotron radiation X-ray diffraction analysis is used to investigate the initial growth dynamics of metal–organic vapor-phase epitaxy-grown ZnO nanorods on c-Al2O3 substrates. A two-dimensional area detector with a grazing-incidence geometry enables projected reciprocal space mapping (RSM) using coordinate transformation of diffraction images. The projected RSM reveals multiple heteroepitaxial relationships between ZnO and Al2O3, including the dominant relationship of ZnO(101̅0)∥Al2O3(21̅1̅0). Evolution of internal strain is revealed by an additional study on diffraction images and θ–2θ scans. Surface topology from atomic force microscopy estimates the growth rate, supported by the Scherrer equation analysis of the θ–2θ diffraction.

HRTex: a high-resolution texture data processing tool for monochromatic neutron diffraction based on the pixel projection method

HRTex is a new texture data processing tool for two-dimensional position-sensitive area detectors on monochromatic neutron diffractometers. With the aim of improving the resolution and accuracy of pole figure calculations, HRTex treats the raw data of the area detector for each pixel and projects the intensity of each pixel directly onto a high-resolution pole figure. With the resultant refinement of the resolution, HRTex can distinguish close texture peaks with a flexible resolution setting and reduced information loss. Test results of HRTex on the data sets of two samples measured by two different neutron facilities are analysed, and the improvements in accuracy, resolution and efficiency of the pole figure calculation are discussed.

Orientation-dependent, field-induced phase transitions in soft lead zirconate titanate piezoceramics

In situ high-energy X-ray diffraction (XRD) was performed on lead-zirconate-titanate-based ferroelectric materials with composition near the morphotropic phase boundary (MPB). The utilization of the two-dimensional area detector in in situ field-dependent experiments enables the complete analysis of the material response with respect to all azimuthal angles at each field amplitude. The studies reveal that the field-induced phase transition from tetragonal to rhombohedral is dependent on crystal orientation in Nb-doped PbZr0.53Ti0.47O3 that is in close compositional proximity to the MPB. However, only domain wall motion is activated in Nb-doped PbZr0.50Ti0.50O3, which is further in composition from the MPB. This synchrotron-based XRD characterization approach illustrates the importance in evaluating the orientation-dependence of phase transitions in piezoelectric and ferroelectric polycrystalline materials.

Visualizing mineralization processes and fossil anatomy using synchronous synchrotron X-ray fluorescence and X-ray diffraction mapping

Fossils, including those that occasionally preserve decay-prone soft tissues, are mostly made of minerals. Accessing their chemical composition provides unique insight into their past biology and/or the mechanisms by which they preserve, leading to a series of developments in chemical and elemental imaging. However, the mineral composition of fossils, particularly where soft tissues are preserved, is often only inferred indirectly from elemental data, while X-ray diffraction that specifically provides phase identification received little attention. Here, we show the use of synchrotron radiation to generate not only X-ray fluorescence elemental maps of a fossil, but also mineralogical maps in transmission geometry using a two-dimensional area detector placed behind the fossil. This innovative approach was applied to millimetre-thick cross-sections prepared through three-dimensionally preserved fossils, as well as to compressed fossils. It identifies and maps mineral phases and their distribution at the microscale over centimetre-sized areas, benefitting from the elemental information collected synchronously, and further informs on texture (preferential orientation), crystallite size and local strain. Probing such crystallographic information is instrumental in defining mineralization sequences, reconstructing the fossilization environment and constraining preservation biases. Similarly, this approach could potentially provide new knowledge on other (bio)mineralization processes in environmental sciences. We also illustrate that mineralogical contrasts between fossil tissues and/or the encasing sedimentary matrix can be used to visualize hidden anatomies in fossils.

Spatial Signal Detection Using Continuous Shrinkage Priors

Motivated by the problem of detecting changes in two-dimensional X-ray diffraction data, we propose a Bayesian spatial model for sparse signal detection in image data. Our model places considerable mass near zero and has heavy tails to reflect the prior belief that the image signal is zero for most pixels and large for an important subset. We show that the spatial prior places mass on nearby locations simultaneously being zero, and also allows for nearby locations to simultaneously be large signals. The form of the prior also facilitates efficient computing for large images. We conduct a simulation study to evaluate the properties of the proposed prior and show that it outperforms other spatial models. We apply our method in the analysis of X-ray diffraction data from a two-dimensional area detector to detect changes in the pattern when the material is exposed to an electric field.

Experimental study of a boron coated straw detector module at CPHS

Large-area position-sensitive thermal neutron detector plays an important role in the small angle neutron scattering (SANS) technique. Considering the shortage of 3He supply, a detector module composed of 64 boron coated straw (BCS) tubes was developed in the present work for the time-of-flight (TOF) SANS instrument that will be deployed on the Compact Pulsed Hadron Source (CPHS) at Tsinghua University. In this paper, 64 straw tubes were tightly packed into 8 rows by 8 columns. A multiplex readout system was utilized to locate the straw tube that has registered a neutron deposition event in the detector module, and to reconstruct the longitudinal position according to the charge division method. Several key aspects, including the pulse height spectrum, the spatial resolution and the position linearity, have been studied using the CPHS neutron beams generated by 3 MeV protons. The results indicated that the detector module can achieve an average axial spatial resolution of 5.8± 0.2 mm with a good position linearity. The neutron detection efficiency of the detector module was simulated with Geant4 code and was found to be larger than 39% for the neutrons at CPHS operated with 13 MeV proton beams in the future. It was concluded that the BCS tubes can be used to build the two-dimensional position-sensitive area detector for the TOF-SANS instrument at CPHS.

The effect of air exposure on the crystal structure of oligo-thiophene thin films investigated using in situ X-ray diffraction

The effect of air exposure on the crystal structure of alkyl substituted organic thin film was studied using in situ grazing incidence X-ray diffraction (GIXD) measurements. The GIXD measurements were carried out by scanning the specific qxy region using a two-dimensional area detector and the Soller slit. The a and b axes of the monoclinic unit cell were found to shrink by air exposure. As for the c axis, there was no detectable change caused by air exposure. The shrinking of the a and b axes immediately occurred after exposure to air, and then saturated in six days. The shrinking of the a and b axes by air exposure might affect the transport properties, because shortening between intermolecular distances should promote the hopping of hole carriers.

A simple approach to determine the polarization coefficient at synchrotron radiation stations

A simple procedure for the measurement of the degree of linear polarization at a synchrotron radiation station is described. The diffraction pattern from a glass plate set perpendicular to the incident beam is registered using a two-dimensional area detector. The intensity variation along the azimuth angle ρ at a constant diffraction angle is fitted to the theoretical cos2ρ dependence. The results of measurements performed at a synchrotron radiation station with a CCD detector on the beam from a bending magnet are presented.

Three-dimensional x-ray diffraction detection and visualization

A new method of sensing and analyzing three-dimensional (3D) x-ray diffraction (XRD) cones was introduced. Using a two-dimensional area detector, a sequence of frames was collected while moving the detector away from the sample with small equally spaced steps and keeping all other parameters constant. A 3D dataset was created from the subsequent frames. The 3D x-ray diffraction (XRD3) pattern contains far more information than a one-dimensional profile collected with the conventional diffractometer and 2D x-ray diffraction (XRD2). The present work discusses some fundamentals about XRD3, such as the data collection method, 3D visualization, diffraction data interpretation and potential applications of XRD3.

Scanning-free grazing emission x-ray fluorescence by means of an angular dispersive arrangement with a two-dimensional position-sensitive area detector

We report on the application of a two-dimensional position-sensitive area detector towards grazing emission x-ray fluorescence (GEXRF) spectroscopy. GEXRF allows for surface-sensitive studies with nanometer-scale accuracy in the depth direction by measuring the intensity variation of an x-ray fluorescence line with the grazing emission angle. The presented experimental setup is based on a fixed sample-detector arrangement and does not require any moving components. We show that the dispersion of the grazing emission angle along a position-sensitive detector allows to acquire with an excellent angular resolution a full GEXRF profile in a single measurement. Moreover, the use of a two-dimensional detector allows to perform experiments with an increased solid angle of detection per emission angle. This results in combination with the nonsequential and simultaneous acquisition of the GEXRF profiles of different emission lines in considerably reduced acquisition times. The realization, the demands, and the main characteristics of the scanning-free GEXRF setup will be presented. A few experimental examples will serve to illustrate the analytical possibilities offered by the presented setup.

Advances inin situpowder diffraction of battery materials: a case study of the new beamline P02.1 at DESY, Hamburg

A brief review ofin situpowder diffraction methods for battery materials is given. Furthermore, it is demonstrated that the new beamline P02.1 at the synchrotron source PETRA III (DESY, Hamburg), equipped with a new electrochemical test cell design and a fast two-dimensional area detector, enables outstanding conditions forin situdiffraction studies on battery materials with complex crystal structures. For instance, the time necessary to measure a pattern can be reduced to the region of milliseconds accompanied by an excellent pattern quality. It is shown that even at medium detector distances the instrumental resolution is suitable for crystallite size refinements. Additional crucial issues like contributions to the background and availableqrange are determined.

A framework for generating synthetic diffraction images from deforming polycrystals using crystal-based finite element formulations

A framework for generating synthetic diffraction images on X-ray detectors from individual grains within polycrystals under in situ loading is described. Crystal plasticity-based finite element simulations of three-dimensional (3D) polycrystalline aggregates undergoing deformation were utilized to mimic a far-field High Energy Diffraction Microscopy (HEDM) experiment. The smearing of the diffraction spots on a two-dimensional (2D) area detector was consistent between the experiment and simulation for a target grain within a polycrystalline sample of a Cu–Cr–Zr alloy. The influence of crystallographic neighborhood and grain shape on the diffracted intensity distributions of the diffraction spots, the stress distribution and the misorientation distribution within a grain is also investigated. Key features of the diffraction spots are examined, differentiating between changes with applied stress and changes due to lattice misorientation associated with plastic straining.

Spatial distribution of the absorption factor for an infinite cylindrical sample used with a two-dimensional area detector

Specialized software has been developed to calculate the absorption factor for the infinite-cylinder transmission Debye–Scherrer geometry (including inclined beams) to be used with two-dimensional area powder pattern registration. The diffracted beams are defined by the direction cosines in the laboratory Cartesian coordinate system. Modern two-dimensional area detectors have a large number of pixels, so an interpolation is made by the triangulation procedure to save computer time. The absorption correction is allowed for so that the intensity in each pixel is reduced on the same scale and the final diffraction-angle-dependent intensity,I(2θ), does not require any further absorption correction.

Sequential femtosecond X-ray imaging

Researchers demonstrate an X-ray holography method that records two independent images spaced by a femtosecond variable time delay. The concept overcomes the time limitations of two-dimensional area detectors by superimposing the separable X-ray holograms in a single detector exposure.

Atomic resolution holography using advanced reconstruction techniques for two-dimensional detectors

Atomic resolution holography is based on two concepts. Either the emitter of the radiation used is embedded in the sample (internal source concept) or, on account of the optical reciprocity law, the detector forms part of the sample (internal detector concept). In many cases, holographic objects (atoms and nuclei) simultaneously adopt the roles of both source and detector. Thus, the recorded image contains a mixture of both inside source and inside detector holograms. When reconstructing one type of hologram, the presence of the other hologram causes serious distortions. In the present work, we propose a new method, the so-called double reconstruction (DR), which not only suppresses the mutual distortions but also exploits the information content of the measured hologram more effectively. This novel approach also decreases the level of distortion arising from diffraction and statistical noise. The efficiency of the DR technique is significantly enhanced by employing two-dimensional (2D) area detectors. The power of the method is illustrated here by applying it to a real measurement on a palladium-hydrogen sample.

A crystallographic investigation of GaN nanostructures by reciprocal space mapping in agrazing incidence geometry

Reciprocal space mapping with a two-dimensional (2D) area detector in a grazing incidencegeometry was applied to determine crystallographic orientations of GaN nanostructures epitaxially grown on a sapphire substrate. By using both unprojected and projectedreciprocal space mapping with a proper coordinate transformation, the crystallographicorientations of GaN nanostructures with respect to that of a substrate were unambiguouslydetermined. In particular, the legs of multipods in the wurtzite phase were found topreferentially nucleate on the sides of tetrahedral cores in the zinc blende phase.

Synchrotron Laue micro-diffraction: a new beam line project at SOLEIL for phase identification and mechanics of materials

Micro-focused x-ray beams from 1 down to less than 0.1 micron in size have been one of the real success stories of 3rd generation synchrotron x-ray machines (SR), thanks to a large panel of focusing devices for hard and soft x-rays [1-5]. There is clearly a rapidly growing need for very small x-ray beams – 10 nm is theoretically possible which allow for non-destructive local scale measurements of structure and chemistry. This need encompasses many different scientific fields: Microelectronics and microsystems, Metallurgy and mechanics, Environmental and earth sciences, Art and archaeology, Life sciences and soft condensed matter. In all these different research fields one would ideally like to get information on a local scale of the structure, the chemical composition and the local atomic environment. This implies performing at the submicron scale: XRD, XRF, EXAFS, XANES. However, the case of XRD technique is specific in the sense that the recorded signal does not only depend on the beam size but also on the ratio of the beam size to the grain size. If this ratio is large enough one is left with powder diffraction when using monochromatic x-ray beam (MB) and the diffraction information is an average over the size of the beam. On the other hand if the beam size over grain size ratio is small one gets single crystals diffraction. It is thus possible to obtain intra grain structural information. Transmission configuration with hard x-rays is done using either MB or white beam (WB) XRD with generally energy dispersive mode. For the proposed beam line, the working geometry is reflection. It is important to realize, however, that recording a significant number of diffraction spots from a single crystal requires either a movement of the sample under the beam (goniometry) or the use of a polychromatic incoming beam (Laue diffraction) combined with a two-dimensional area detector such as CCD type. Since there are no available goniometers with a sphere of confusion (SOC) radius smaller than the micrometer x-ray probe size it is thus necessary to use WB. Details concerning the different applications of the technique may be found for instance at the Advanced Light Source (ALS) web site address (http://xraysweb.lbl.gov/microdif/index.htm), this synchrotron source being close enough to the French facility SOLEIL. This beam line project is unique in Europe since there is almost nothing in European countries in terms of fully dedicated WB μXRD beam line except the BM32 project at ESRF (10 % of the full beam line time dedicated to microfocus WB during 3 years). The Scientific Advisory Committee (SAC) of SOLEIL approved the APS (preliminary beam line project*) in November 2005 and the SOLEIL Council decided in July 2006 to build this additional beam line and to provide 1⁄4 of the total beam line budget which will be completed by external funds (not yet found).

Texture and phase analysis of a Ca3Co4O9∕Si (100) thermoelectric film

This paper reports the texture analysis as well as the identification of two crystalline phases between a thin film of monoclinic Ca3Co4O9 and a cubic (100) Si substrate, using a diffractometer equipped with a two-dimensional area detector. No reflections other than 00ℓ were observed in the symmetric configuration using an x-ray powder diffraction scan (Bragg-Brentano geometry). Pole figures collected for six reflections using asymmetric configurations did not show ab-plane epitaxial relationships between the film and the substrate. These results establish the Ca3Co4O9 fiber texture of the film with the (001) pole parallel to the surface normal. Single-crystal-like second phases, CaCoSi2O6 and CoO, presumably the interface reaction products of Ca3Co4O9 with the substrate Si, were identified. The near four-fold symmetry and the similar intensity displayed by the 220 reflection from the CaCoSi2O6 structure indicated an epitaxial relation between CaCoSi2O6 and Si, with four symmetry-induced variants being generated with approximately equal volume fractions.

Investigation of Phase Transition in Stacked Ge-Chalcogenide/SnTe Phase-change Memory Films

ABSTRACTPhase transitions in stacked GeTe/SnTe and Ge2Se3/SnTe thin layers for potential phase-change memory applications have been investigated by X-ray diffraction using a two-dimensional area detector system. The as-deposited underlying GeTe or Ge2Se3 layer is amorphous, whereas the top SnTe layer is crystalline. In the GeTe/SnTe stack, the crystallization of GeTe phase occurs near 170°C, and upon further heating, the GeTe phase disappears, followed by the formation of rocksalt-structured GexSn1−xTe solid solution. In the Ge2Se3/SnTe stack, the phase transition starts with the separation of a SnSe phase due to the migration of Sn ions into the Ge2Se3 layer. SnSe is believed to facilitate the crystallization of Ge2Se3-SnTe solid solution at ∼360°C, which is much lower than the crystallization temperature of Ge2Se3, therefore consuming less power during the phase transition.