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The x-ray dark-field contrast accessible via grating interferometry is sensitive to features at length scales well below what is resolvable by a detector system. It is commonly explained as arising from small-angle x-ray scattering (SAXS), and can be implemented both at synchrotron beamlines and with low-brilliance sources such as x-ray tubes. Here, we demonstrate that for tube based setups the underlying process of image formation can be fundamentally different. For focal spots or detector pixels that comprise multiple grating periods, we show that dark-field images contain a strong artificial and system-specific component not arising from SAXS. Based on experiments carried out with a nanofocus x-ray tube and the example of an excised rat lung, we demonstrate that the dark-field contrast observed for porous media transforms into a differential phase contrast for large geometric magnifications. Using a photon counting detector with an adjustable point spread function, we confirm that a dark-field image can indeed be formed by an intra-pixel differential phase contrast that cannot be resolved as such due to a dephasing between the periodicities of the absorption grating and the Talbot carpet. Our findings are further corroborated by a link between the strength of this pseudo-dark-field contrast and our x-ray tube's focal spot size in a three-grating setup. These results must not be ignored when measurements are intended to be reproducible across systems.

The enhancement of the Raman light scattering signal from the surface of the porous hybrid biocomposites based on polyhydroxybutyrate (PHB), calcium carbonate (CaCO3), and nanoplasmonic Ag particles is investigated. Based on PHB, fibrous scaffolds are obtained by the electrospinning technique. The fibrous scaffolds have been covered by CaCO3 and Ag nanoparticles by means of mineralization in salt solutions and Ag reduction reaction. Successful formation of the CaCO3 and Ag nanoparticles on the scaffold surface has been confirmed by the data of scanning electron microscopy, x-ray diffraction analysis, and infrared spectroscopy. Surface-enhanced Raman spectroscopy (SERS) of the obtained sample surface has demonstrated a significant enhancement of the Rhodamine 6G signal (Ef > 105) in comparison with the reference sample where the analyte concentration and the laser power were 100 times higher. Thus, the present research has confirmed prospects for the application of biocomposites based on polyhydroxybutyrate for detection and investigation of biomolecules by the SERS method. [ABSTRACT FROM AUTHOR]

A procedure for obtaining three-dimensionally resolved reciprocal-space maps in a skew X-ray diffraction geometry is described. The geometry allows tuning of the information depth in the range from tens of micrometres for symmetric skew diffraction down to tens of nanometres for strongly asymmetric skew geometries, where the angle of incidence is below the critical angle of total external reflection. The diffraction data are processed using a rotation matrix formalism. The whole three-dimensional reciprocal-space map can be measured by performing a single azimuthal rotation of the sample and using a two-dimensional detector, while keeping the angle of incidence and the X-ray information depth fixed (FIXD method). Having a high surface sensitivity under grazing-incidence conditions, the FIXD method can be applied to a large variety of Bragg reflections, particularly polar ones, which provide information on strain and chemical composition separately. In contrast with conventional grazing-incidence diffraction, the FIXD approach reveals, in addition to the lateral (in-plane) components, the vertical (out-of-plane) component of the strain field, and therefore allows the separation of the scattering contributions of strained epitaxial nanostructures by their vertical misfit. The potential of FIXD is demonstrated by resolving the diffraction signal from a single layer of InGaN quantum dots grown on a GaN buffer layer. The FIXD approach is suited to the study of free-standing and covered near-surface nano-objects, as well as vertically extended multilayer structures. [ABSTRACT FROM AUTHOR]

Quantitative characterization of local strain in silicon wafers is critical in view of issues such as wafer handling during manufacturing and strain engineering. In this work, full-field X-ray microdiffraction imaging using synchrotron radiation is employed to investigate the long-range distribution of strain fields in silicon wafers induced by indents under different conditions in order to simulate wafer fabrication damage. The technique provides a detailed quantitative mapping of strain and defect characterization at the micrometer spatial resolution and holds some advantages over conventional methods. [ABSTRACT FROM AUTHOR]

The apparatus for X-ray diffraction imaging (XRDI) of 450-mm wafers, is now placed at the ANKA synchrotron radiation source in Karlsruhe, is described in the context of the drive to inspect wafers for plastic deformation or mechanical damage. It is shown that full wafer maps at high resolution can be expected to take a few hours to record. However, we show from experiments on 200-, 300-, and 450-mm wafers that a perimeter-scan on a 450-mm wafer, to pick up edge damage and edge-originated slip sources, can be achieved in just over 10 min. Experiments at the Diamond Light Source, on wafers still in their cassettes, suggest that clean-room conditions may not be necessary for such characterization. We conclude that scaling up of the 300-mm format Jordan Valley tools, together with the existing facility at ANKA, provides satisfactory capability for future XRDI analysis of 450-mm wafers. [ABSTRACT FROM PUBLISHER]

Synchrotron radiation laminography with X-ray diffraction contrast enables three-dimensional imaging of dislocations in monocrystalline wafers. We outline the principle of the technique, the required experimental conditions, and the reconstruction procedure. The feasibility and the potential of the method are demonstrated by three-dimensional imaging of dislocation loops in an indent-damaged and annealed silicon wafer. [ABSTRACT FROM AUTHOR]

Babcock Noell GmbH (BNG) is completing the fabrication of a 1.5 m long superconducting insertion device for the Karlsruhe Institute of Technology (KIT). The unit is planned to be installed in the ANKA storage ring at the end of 2010 to become the light source of the new beamline NANO for high resolution X-ray diffraction. The period length of the device is 15 mm for a total of 100.5 full periods plus an additional matching period at each end. The key specifications of the system are: a K value higher than 2 for a magnetic gap of 5 mm, the capability of withstanding a 4 W beam heat load and a phase error smaller than 3.5 degrees. The superconducting coils have been qualified by means of a vertical test in liquid helium at CERN and are ready to be installed in the cryostat. This paper describes the main features of the system. [ABSTRACT FROM AUTHOR]

We used high-resolution x-ray reciprocal space mapping in noncoplanar grazing-incidence geometry for the determination of the density of edge threading dislocations in c-oriented GaN epitaxial layers and we compared the measured intensity distributions with results of numerical Monte Carlo simulations of diffuse scattering. We demonstrated that a combination of diffraction data taken in coplanar symmetric and noncoplanar grazing-incidence geometries makes it possible to obtain the densities of screw and edge threading dislocations. [ABSTRACT FROM AUTHOR]

Space-resolved x-ray diffraction measurements of gradient-etched CuIn1-xGaxSe2 (CIGS) solar cells provide information about stress and texture depth profiles in the absorber layer. An important parameter of CIGS layer growth dynamics, the absorber thickness-dependent stress in the molybdenum back contact, is analyzed. Texturing of grains and quality of the polycrystalline absorber layer are correlated with the intentional composition gradients (band gap grading). The band gap gradient is determined by space-resolved photoluminescence measurements and correlated with composition and strain profiles. [ABSTRACT FROM AUTHOR]

The depth dependent strain relaxation in photolithographically defined and reactive ion etched Si/SiGe quantum wire and dot arrays is determined by high resolution grazing incidence x-ray diffraction. The laterally periodic structures were aligned along two orthogonal [110] and [1¯10] directions on the (001) surface. By recording reciprocal space maps around the (220) and (2¯20) reciprocal lattice points, the shape and in-plane strain could be determined independently of each other. Using triple axis diffractometry and changing the effective penetration depth of the x-ray radiation between 5 and 300 nm the strain relaxation in the wires and dots could be determined depth resolved. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the x-ray diffraction reciprocal space mapping of GaAs surface grating. Cross pattern of satellite rods and grating transmission substrate reflection resonance peaks; Diffraction features of monocrystalline semiconductor grating with periodicity of 574 nanometer.

Europium silicide nanoislands and films with Eu coverage in the range 0.3 ML–303 ML were grown on the vicinal Si(001) surface with 4° miscut towards [110] by molecular beam epitaxy. The nanostructures were characterized by atomic force microscopy, reflection high energy electron diffraction, in situ synchrotron radiation X-ray absorption near edge structure spectroscopy and ex situ X-ray diffraction. The analysis revealed the formation of EuSi 2 with a tetragonal structure. By increasing the Eu coverage the surface morphology gradually changes from isolated islands through films with very rough surface to thick films with smoother surface. [ABSTRACT FROM AUTHOR]

Abstract: High resolution X-ray coplanar (symmetric X-ray diffraction (SXRD) and asymmetric X-ray diffraction (ASXRD)) and non-coplanar diffraction (grazing incidence diffraction (GID)) have been used to investigate the quality of AlGaN epilayers with 20% Al content, grown on sapphire using SiN x interlayers. The measurement of reciprocal space maps (RSM) with higher orders of reflections of SXRD and ASXRD which is readily performed at the synchrotron with high resolution and intensity reveals the presence of several diffraction peaks originating from the occurrence of local differences in the lattice constants. Two distinguishable AlGaN phases having different crystalline parameters were clearly recognized from X-ray data and the corresponding densities of screw dislocations have been determined measured as function of the overgrowth thickness varying from 0.5μm to 3.5μm. The variation of the screw and edge type dislocation densities with the overgrowth thickness has been found to follow the scaling law h −n where h is the thickness of the buffer layer. [Copyright &y& Elsevier]

Abstract: Experimental data are presented on the structure and properties of hardening nanocrystalline copper-added titanium nitride coatings produced by plasma-assisted vacuum arc evaporation of sintered cathodes. A model of the nanostructurization of this type of coating is proposed. According to the model, the nanocrystallization in these materials is due to the added atoms, which form an amorphous sheath around a grain that restricts the grain growth. [Copyright &y& Elsevier]

Abstract: Titanium beryllide Be12Ti and vanadium beryllide Be12V are considered to be promising materials for advanced neutron multipliers in the helium-cooled breeding blanket of DEMO reactor. A study of the surface layers of oxidized beryllide specimens by means of powder X-ray diffraction technique is presented in this work. The phase composition of the near-to-surface layers of Be12Ti and Be12V specimens was investigated at the Single Crystal Diffraction (SCD) beamline at ANKA synchrotron facility after air-annealing at 800°C. A high surface sensitivity of measurements was achieved at grazing incidence conditions by varying the incidence angle. Since beryllium has low values of X-ray absorption, the near-surface regions having depths from 2 up to 20μm were investigated. The main objective of the work is the evaluation of composition of the reactant products which can influence the parameters of retention and release of radiogenic gases. [Copyright &y& Elsevier]

Abstract: Self-organized, buried InAs quantum dots covered by an AlAs diffusion barrier were investigated under UHV conditions using grazing incidence X-ray diffraction. The experimental data is compared to the simulated results obtained by Finite Element Method and Distorted Wave Born Approximation. We have found that the simulated data could be compared to the experimental one only after convolution by the resolution element which can be estimated from the experiment. By adjusting the simulation parameters we were able to find good agreement between the simulated and the measured data. [Copyright &y& Elsevier]

Coherent x-ray diffractive imaging is extended to high resolution strain analysis in crystalline nanostructured devices. The method now enables reconstruction of elastic strain distribution in layered nanowires or dots. The application potential is demonstrated by determining the strain distribution in (Ga,Mn)As/GaAs nanowires. By separating diffraction signals in reciprocal spaces, individual parts of the device could be reconstructed independently by our inversion procedure. We demonstrate the method to be effective for material specific reconstruction of strain distribution in highly integrated devices. [ABSTRACT FROM AUTHOR]

Abstract: White beam X-ray diffraction imaging (topography) with an optimised CCD-detector system is used to monitor in-situ and in real time the nucleation, growth and movement of dislocations in silicon at high temperatures. It can be shown, that damage like microcracks and the surrounding strain fields in a wafer act as sources for dislocation loops, which end in slip bands far away from the source. The dislocations are arranged in channels of parallel {111} glide planes, which become visible as bands of parallel surface steps when the dislocations slip out on the back or front sides of the wafer. The width of such a channel or band depend on the dimensions of the damaged volume where the dislocations nucleate. This can be explained with a simple geometrical model. [Copyright &y& Elsevier]

Abstract: Rocking curve imaging is based on measuring a series of Bragg-reflection digital topographs by monochromatic parallel-beam synchrotron radiation in order to quantify local crystal lattice rotations within a large surface area with high angular and high spatial resolution. In this paper we apply the method to map local lattice tilts in two distinct semiconductor sample types with lattice misorientations up to and with spatial resolution from 30  down to 1 . We analyse the measured surface-tilt data volumes for samples with almost smoothly varying specific misoriented defect formation in GaAs wafers and for an inherent subsurface grain structure of epitaxial lateral overgrowth wings in GaN. Back-projected tilt maps and histograms provide both local and global characteristics of the microcrystallinity. [Copyright &y& Elsevier]

Abstract: Hybrid pixel detectors, with the X-ray conversion layer and the readout electronics realised in two separate semiconducting crystals, offer the unique possibility to observe effects of dynamical diffraction directly in a crystal sensor. The sensor can be used to Bragg diffract X-rays in transmission geometry and simultaneously to observe the wave fields generated inside the sensor through absorption thus producing signals in the pixel readout. A monochromatic beam of sufficiently high energy is used to obtain a large absorption length inside the sample. This allows to use a setup geometry with the narrow incident beam hitting from the side of the platelet-shaped sensor, parallel to the readout electronics, so that the whole Borrmann triangle can be observed inside the sample. We used a Medipix2 detector with a silicon sensor layer to observe diffraction in both transmission and reflection geometry. [Copyright &y& Elsevier]

Correlated x-ray diffraction imaging and light microscopy provide a conclusive picture of three-dimensional dislocation arrangements on the micrometer scale. The characterization includes bulk crystallographic properties like Burgers vectors and determines links to structural features at the surface. Based on this approach, we study here the thermally induced slip-band formation at prior mechanical damage in Si wafers. Mobilization and multiplication of preexisting dislocations are identified as dominating mechanisms, and undisturbed long-range emission from regenerative sources is discovered. [ABSTRACT FROM AUTHOR]