Synchrotron Bragg diffraction imaging characterization of synthetic diamond crystals for optical and electronic power device applications.

Bragg diffraction imaging enables the quality of synthetic single-crystal diamond substrates and their overgrown, mostly doped, diamond layers to be characterized. This is very important for improving diamond-based devices produced for X-ray optics and power electronics applications. The usual first step for this characterization is white-beam X-ray diffraction topography, which is a simple and fast method to identify the extended defects (dislocations, growth sectors, boundaries, stacking faults, overall curvature etc.) within the crystal. This allows easy and quick comparison of the crystal quality of diamond plates available from various commercial suppliers. When needed, rocking curve imaging (RCI) is also employed, which is the quantitative counterpart of monochromatic Bragg diffraction imaging. RCI enables the local determination of both the effective misorientation, which results from lattice parameter variation and the local lattice tilt, and the local Bragg position. Maps derived from these parameters are used to measure the magnitude of the distortions associated with polishing damage and the depth of this damage within the volume of the crystal. For overgrown layers, these maps also reveal the distortion induced by the incorporation of impurities such as boron, or the lattice parameter variations associated with the presence of growth-incorporated nitrogen. These techniques are described, and their capabilities for studying the quality of diamond substrates and overgrown layers, and the surface damage caused by mechanical polishing, are illustrated by examples.

Characterization of defects in mono-like silicon for photovoltaic applications using X-ray Bragg diffraction imaging.

Rocking curve imaging (projection and section X-ray topography) has been used to study the generation and propagation of defects at the junctions between and above the seed crystals in mono-like silicon ingots. The images of different kinds of defects such as precipitates, dislocations and twins in the integrated intensity, full width at half-maximum and peak position maps resulting from the experiment have been studied. The qualitative and quantitative information that can be extracted from these maps, in particular the contrast of the images of the various defects, is discussed. These defects have a detrimental effect on solar cell efficiency and their detailed investigation allows clues to be obtained in order to improve the growth process. This work shows that synchrotron X-ray diffraction imaging techniques, because of their high angular resolution (<10-4°) and large field of view (several mm2), constitute a powerful tool for investigating the initial stages of growth of directionally solidified mono-like silicon.

Inception and movement of a 'subgrain boundary precursor' in ice under an applied stress, observed by X-ray synchrotron radiation Bragg imaging.

Basal slip of dislocations, the easiest deformation mechanism of ice crystals, does not allow a response to any strain state. The first steps of another mechanism, with a moving subgrain boundary precursor region, which permits accommodating the effect of an applied load, is investigated on an ice single crystal, mainly using synchrotron radiation Bragg diffraction imaging. During this process, the evolution of the local integrated intensity shows that there is both a general multiplication of dislocations within the crystal and a movement of basal dislocations towards the surface. The 'subgrain boundary precursor' region evolves towards a classical grain boundary when further deformed.

On the implementation of computed laminography using synchrotron radiation.

Hard x rays from a synchrotron source are used in this implementation of computed laminography for three-dimensional (3D) imaging of flat, laterally extended objects. Due to outstanding properties of synchrotron light, high spatial resolution down to the micrometer scale can be attained, even for specimens having lateral dimensions of several decimeters. Operating either with a monochromatic or with a white synchrotron beam, the method can be optimized to attain high sensitivity or considerable inspection throughput in synchrotron user and small-batch industrial experiments. The article describes the details of experimental setups, alignment procedures, and the underlying reconstruction principles. Imaging of interconnections in flip-chip and wire-bonded devices illustrates the peculiarities of the method compared to its alternatives and demonstrates the wide application potential for the 3D inspection and quality assessment in microsystem technology.

The radiotherapy clinical trials projects at the ESRF: technical aspects.

The radiotherapy clinical trials projects, both aiming at treating aggressive brain tumors, require several major modifications and new constructions at the ESRF ID17 Biomedical beamline. The application of the Stereotactic Synchrotron Radiation Therapy (SSRT) technique mainly necessitates an upgrade of the existing patient positioning system, which was formerly used for the angiography program. It will allow for accurate positioning, translation and rotation of the patient during the treatment. For the Microbeam Radiation Therapy (MRT) clinical trials project, a new white beam hutch will be constructed to accommodate a dedicated patient positioning system. Consequently, the existing control hutches and the related installations will also be completely refurbished. Furthermore, the foreseen installation of a second X-ray source, which will allow doubling the currently available photon flux at high energies, requires a redesign of most optical components to handle the increased power and power densities. Starting from the current ID17 Biomedical beamline layout, the paper will present an update of the different modification/construction projects, including the general organization and planning.

In situ and real-time probing of quasicrystal solidification dynamics by synchrotron imaging.

Quasicrystal growth remains an unsolved problem in condensed matter. The dynamics of the process is studied by means of synchrotron live imaging all along the solidification of icosahedral AlPdMn quasicrystals. The lateral motion of ledges driving faceted growth at the solid-melt interface is conclusively shown. When the solidification rate is increased, nucleation and free growth of new faceted grains occur in the melt due to the significant interface recoil induced by slow attachment kinetics. The detailed analysis of the evolution of these grains reveals the crucial role of aluminum rejection, both in the poisoning of their growth and driving fluid flow.

Present state and perspectives of synchrotron radiation diffraction imaging.

The modern third-generation synchrotron radiation sources offer enhanced possibilities for all variants of imaging techniques. The quantitative and qualitative improvements with respect to previous synchrotron diffraction imaging work, which include the investigation in transmission of bulky samples, the use, as an additional parameter, of the sample-to-detector distance, and the use of the coherence of the beam, are illustrated by several examples. Emphasis is given to the possibilities associated with modern electronic detectors for this type of imaging. The new techniques implemented at the ESRF that take full advantage of new capabilities, and more particularly that of 'topo-tomography', are presented.

Phase-contrast imaging of thin biomaterials.

The necessity of information about the inner microscopical features of low absorbing materials is one of the most important goals in the structural research field. So far, non destructive analysis have been performed using contact radiography giving the scope for great advances in the production and application of new materials. However, the nature of interaction, namely X-ray absorption, limited the observations only to materials having sufficient heavy elements content. The adoption of a different X-ray interaction with matter which involves refractive properties of materials is at the basis of phase-contrast imaging. The novel method allows the use of high X-ray energies, for a deeper penetration and a lower released dose, without losing any information on the nature of the sample. A demonstration study, performed at the third generation European Synchrotron Radiation Facility (ESRF)-Grenoble, to show the potential of the new technique applied to biomaterials characterization is presented here. The test samples are a commercial matrix barrier (GUIDOR) intended to aid the healing process after periodontal surgery and a hydroxyapatite thin slab originally deposited by plasma spray technique on a TA6V alloy substrate. Phase-contrast images showed significant advantages revealing features that have negligible absorption contrast. The technique can be successfully used for the characterization of biomaterials.

Perspectives in three-dimensional analysis of bone samples using synchrotron radiation microtomography.

In this paper we present a methodology based on 3D synchrotron radiation microtomography to analyze non-destructively 3D bone samples. After a technical presentation of the imaging system and the image analysis techniques, we report results on three-dimensional analysis of vertebral samples from women of different ages. The new capabilities of this technique for the investigation of bone are discussed. They include a high spatial resolution down to the micron level, a high density resolution allowing a local quantification of bone mineralization, phase contrast imaging and advances in 3D image analysis.

Phase imaging using highly coherent X-rays: radiography, tomography, diffraction topography.

Several hard X-rays imaging techniques greatly benefit from the coherence of the beams delivered by the modern synchrotron radiation sources. This is illustrated with examples recorded on the 'long' (145 m) ID19 'imaging' beamline of the ESRF. Phase imaging is directly related to the small angular size of the source as seen from one point of the sample ('effective divergence' approximately microradians). When using the ;propagation' technique, phase radiography and tomography are instrumentally very simple. They are often used in the 'edge detection' regime, where the jumps of density are clearly observed. The in situ damage assessment of micro-heterogeneous materials is one example of the many applications. Recently a more quantitative approach has been developed, which provides a three-dimensional density mapping of the sample ('holotomography'). The combination of diffraction topography and phase-contrast imaging constitutes a powerful tool. The observation of holes of discrete sizes in quasicrystals, and the investigation of poled ferroelectric materials, result from this combination.

A synchrotron radiation microtomography system for the analysis of trabecular bone samples.

X-ray computed microtomography is particularly well suited for studying trabecular bone architecture, which requires three-dimensional (3-D) images with high spatial resolution. For this purpose, we describe a three-dimensional computed microtomography (microCT) system using synchrotron radiation, developed at ESRF. Since synchrotron radiation provides a monochromatic and high photon flux x-ray beam, it allows high resolution and a high signal-to-noise ratio imaging. The principle of the system is based on truly three-dimensional parallel tomographic acquisition. It uses a two-dimensional (2-D) CCD-based detector to record 2-D radiographs of the transmitted beam through the sample under different angles of view. The 3-D tomographic reconstruction, performed by an exact 3-D filtered backprojection algorithm, yields 3-D images with cubic voxels. The spatial resolution of the detector was experimentally measured. For the application to bone investigation, the voxel size was set to 6.65 microm, and the experimental spatial resolution was found to be 11 microm. The reconstructed linear attenuation coefficient was calibrated from hydroxyapatite phantoms. Image processing tools are being developed to extract structural parameters quantifying trabecular bone architecture from the 3-D microCT images. First results on human trabecular bone samples are presented.

Conserving the coherence and uniformity of third-generation synchrotron radiation beams: the case of ID19, a 'long' beamline at the ESRF.

The lateral coherence length is of the order of 100 micron at the 'long' (145 m) ID19 beamline of the ESRF, which is mainly devoted to imaging. Most of the optical elements located along the X-ray path can thus act as ;phase objects', and lead to spurious contrast and/or to coherence degradation, which shows up as an enhanced effective angular size of the source. Both the spurious contrast and the coherence degradation are detrimental for the images (diffraction topographs, tomographs, phase-contrast images) produced at this beamline. The problems identified and the way they were solved during the commissioning of ID19 are reported. More particularly, the role of the protection foils located in the front end, the beryllium windows, the filters and the monochromator defects (scratches, dust, small vibrations) is discussed.

Fractional Talbot imaging of phase gratings with hard x rays.

Fractional Talbot images of optical gratings acting as periodic phase objects have been obtained by use of x rays of 0.069-nm wavelength from a third-generation synchrotron radiation source. Quantitative evaluation of the data obtained as a function of defocusing distance provides information on the lateral coherence of the beam as well as on the phase modulation in the object.

New features of dislocation images in third-generation synchrotron radiation topographs.

Some aspects of the dislocation contrast observed at third-generation synchrotron radiation set-ups are presented. They can be explained by taking into account angular deviation effects on the beam propagation, which are visible because of the ;almost plane-wave' character of these sources. In particular, we show how the evolution of the direct image width of a dislocation as a function of the sample-to-film distance can allow a complete determination of the Burgers vector, i.e. in sign and modulus. In addition, experimental results obtained in monochromatic beam topography are compared with simulated images calculated assuming plane-wave illumination and are demonstrated to show a satisfactory agreement. The utility of the weak-beam technique in enhancing the spatial resolution is demonstrated and a criterion for the selection of experimental conditions depending upon the required spatial resolution, signal-to-noise ratio and exposure time is presented.