J.-F. Berar

Modeling of line-shape asymmetry in powder diffraction

Theoretical calculation shows that suitable approximations of the line-shape asymmetry in powder diffraction profiles should be represented by functions having limited codomains.

A pixel detector with large dynamic range for high photon counting rates

In this paper, results obtained from a prototype photon counting detector are presented. The pixel size is 330 µm × 330 µm for a total area of 16 µm × 40 mm. The detector works at room temperature and its dynamic response ranges from 0.01 up to 106 photons pixel−1 s−1. An energy resolution of about 1.5 keV has been measured. Very encouraging small-angle X-ray scattering (SAXS) and diffraction patterns were obtained, demonstrating the success of the prototype. Plans for future developments based on this study are presented.

A cell for in situ dynamic X-ray diffraction studies: application to the dehydration of zeolite SrX

A new compact cell for in situ synchrotron X-ray diffraction studies of adsorption or catalysis reactions has been designed to enable high performance whilst minimizing difficulties in use. It includes a system for simple insertion and alignment of capillary samples and an original miniaturized furnace providing excellent temperature homogeneity along the sample (temperature gradient less than 1 K over a 6 mm zone at 530 K). The efficiency of this setup is illustrated by in situ characterization of a zeolite (SrX) at four hydration levels.

Energy resolution of the CdTe-XPAD detector: calibration and potential for Laue diffraction measurements on protein crystals.

The XPAD3S-CdTe, a CdTe photon-counting pixel array detector, has been used to measure the energy and the intensity of the white-beam diffraction from a lysozyme crystal. A method was developed to calibrate the detector in terms of energy, allowing incident photon energy measurement to high resolution (approximately 140 eV), opening up new possibilities in energy-resolved X-ray diffraction. In order to demonstrate this, Laue diffraction experiments were performed on the bending-magnet beamline METROLOGIE at Synchrotron SOLEIL. The X-ray energy spectra of diffracted spots were deduced from the indexed Laue patterns collected with an imaging-plate detector and then measured with both the XPAD3S-CdTe and the XPAD3S-Si, a silicon photon-counting pixel array detector. The predicted and measured energy of selected diffraction spots are in good agreement, demonstrating the reliability of the calibration method. These results open up the way to direct unit-cell parameter determination and the measurement of high-quality Laue data even at low resolution. Based on the success of these measurements, potential applications in X-ray diffraction opened up by this type of technology are discussed.

Application of a hybrid pixel detector to powder diffraction

Results obtained using a hybrid pixel photon-counting detector in powder diffraction experiments are presented. The detector works at room temperature and its dynamic response ranges from 0.01 photons pixel(-1) s(-1) up to 10(6) photons pixel(-1) s(-1). The pixel sizes are 0.33 mm x 0.33 mm for a total area of 68 mm x 68 mm. On recording high-resolution diffraction patterns of powders, a reduction of the experimental time by more than a factor of 20 is obtained without loss of data quality. The example of an X-zeolite shows that such detectors can be used for very demanding anomalous experiments. In situ experiments of quenching liquid oxides show that frames of 0.01 s can be achieved for studying such processes.

XPAD: pixel detector for material sciences

Currently available 2D detectors do not make full use of the high flux and high brilliance of third generation synchrotron sources. The XPAD prototype, using active pixels, has been developed to fulfil the needs of materials science scattering experiments. At the time, its prototype is build of eight modules of eight chips. The threshold calibration of /spl ap/4 10/sup 4/ pixels is discussed. Applications to powder diffraction or SAXS experiments prove that it allows to record high quality data.

XPAD : pixel detector for material sciences

Currently available 2D detectors do not make full use of the high flux and high brilliance of third generation synchrotron sources. The XPAD prototype, using active pixels, has been developed to fulfil the needs of materials science scattering experiments. At the time, its prototype is build of eight modules of eight chips. The threshold calibration of /spl ap/4 10/sup 4/ pixels is discussed. Applications to powder diffraction or SAXS experiments prove that it allows to record high quality data.

Performance and Applications of the CdTe- and Si-XPAD3 photon counting 2D detector

The XPAD3 is the third generation of a single photon counting chip developed in collaboration by SOLEIL Synchrotron, the Institut Neel and the Centre de Physique de Particules de Marseille (CPPM). The chip contains 9600 pixels of 130 μm side and a counting electronic chain with an adjustable low level threshold in each pixel. Imaging and detection performance (detective quantum efficiency, modulation transfer function and energy resolution) of the XPAD3 detectors hybridized with Si and CdTe sensors have been evaluated and compared using monochromatic synchrotron X-rays beam. A second version of the chip, optimized for pump-probe experiments, has been realized and successfully tested. Three 7.3 cm x 12.5 cm Si-XPAD3 imagers, composed of 8 silicon modules (7 chips per module) and one 2.1 cm x 3.1 cm CdTe-XPAD3 imager (4 chips) have been constructed and successfully used for synchrotron diffraction experiments and biomedical imaging.

Epitaxial stabilization of SmNiO3 films on (0 0 1) SrTiO3 substrates

The epitaxial stabilization of SmNiO3 (SNO) films grown by an injection MO-CVD process on (0 0 1) SrTiO3 (STO) substrates is discussed. By means of high-resolution x-ray diffraction, we show for the first time that SNO can be stabilized on STO with a minor amount of secondary phases and with a layer thickness reaching several hundreds of nanometres. It is argued that this stabilization is achieved because the lattice mismatch between these two perovskites is not as high as expected (1.8% instead of 2.8%). Moreover, the well-known dissociation of the SNO phase into NiO and Sm2O3 has been clearly correlated with the relaxation of epitaxial strain which is driven by the formation of misfit dislocations.

Rigidity transitions and intermediate structures of Ge–Se glasses – An anomalous X-ray scattering study

Abstract Anomalous X-ray scattering experiments on glassy GexSe1−x have been carried out at energies close to the Ge and Se K edges in a wide concentration range from x=0.15 to 0.333 across the rigidity percolation threshold. The total structure factors S(Q) show considerable variations in both the position and intensity of the prepeak around 10 nm−1, while in the remaining Q range, it stays almost unchanged. The differential structure factors ΔiS(Q) comprise characteristic features. Comparing them suggests that the prepeak purely originates from the Ge–Ge correlation. The threshold is characterized by the percolation of two-Se-linked Ge(Se1/2)4 tetrahedra distributed all over the network as proposed by Feltz et al.