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Diffraction instruments using filtering by one or several analyser crystals exist since the 1980s and 1990s at synchrotron radiation sources, but, due to its low efficiency, this filtering is little used on laboratory sources. In order to overcome this limitation, the efficiency of a small diffraction filtering multi-analyzer block (MAD block) realized with a 'single-crystal-comb' curved on a rigid support is demonstrated here. The geometry of this curved surface is logarithmic spiral and is optimized to allow multi-filtering over a relatively important diffraction angular range and to be also applicable over an X-ray spectral range. The efficiency of such a small rigid-compact MAD block consisting of this singlecrystal-comb generating 20-50 Si(111) single-crystal blades, associated with a block of Soller collimators, is demonstrated. The angle between each crystal is 0.1, so the measurement range of the comb is 2-5°. The geometry of this system has been optimized for operation with a synchrotron X-ray source over an energy range of 22 keV to 46 keV and could be used with laboratory X-ray sources (Ag Kα1, 22.1 keV). This MAD block complements and exploits the qualities of the 'photon-counting' detectors which have very low intrinsic noise. Their joint efficacy is supported by powder pattern measurements of a LaB6 reference sample and of several heterogeneous samples of cultural heritage materials, carried out at 22 keV on the D2AM beamline at the ESRF. Their signal-to-noise ratio is excellent (1000/1) and allows the detection thresholds of the measurements (from 3-1% to 0.1%) to detect minor phases in the studies of 'real' heterogeneous materials to be drastically improved. [ABSTRACT FROM AUTHOR]

The authors have studied the structural evolution of the fragile glass-forming liquid CaAl2O4 during supercooling from the stable liquid phase to the cold glass below Tg. The evolution is characterized by a sharpening of the first diffraction peak and a shortening of the average nearest-neighbor bond length around 1.25Tg, indicating an increase in the degree of both intermediate-range and short-range orders occurring close to the dynamical crossover temperature. The cooling curve developed a kink at this temperature, indicating a simultaneous change in thermodynamic properties. [ABSTRACT FROM AUTHOR]

A one dimensional periodic vicinal surface of sapphire was obtained through a self-ordering process after high-temperature thermal treatment. The morphology of the surface is described as an assembly of prisms exhibiting a rectangular base and a triangular profile orthogonal to the mean surface. Careful measurements of the whole 3D reciprocal map around the origin of the reciprocal space were performed through grazing incidence small-angle X-ray scattering experiments combined with a strict orientation procedure with respect to specific crystallographic directions of the sapphire crystal. We were thus able to determine accurately the actual shape of the prisms, which exhibit an isosceles triangular profile. Such a profile symmetric with respect to a plane normal to the mean sapphire vicinal surface has never been reported. [ABSTRACT FROM AUTHOR]

The crystallization behavior of Ge2Sb2Te5 nanometric clusters was studied using X-ray diffraction with in situ annealing. Clusters were made using a sputtering gas-phase condensation source, which allowed for the growth of well-defined, contaminant-free, and isolated clusters. The average size for the clusters is 5.7 ± 1 nm. As-deposited amorphous clusters crystallize in the fcc cubic phase at 180 °C, while for thin films, the phase change temperature is 155 °C. This observation illustrates the scalability of the Ge2Sb2Te5 phase change from the amorphous to the cubic state in three-dimensionally confined systems in this size range. [ABSTRACT FROM AUTHOR]

Good knowledge of the far-infrared and millimeter emission from dust in the interstellar medium is important to get reliable estimates of the dust mass, to trace and understand the evolution of prestellar structures, and to accurately subtract the foreground emission in the cosmological background anisotropy measurements. Up to now the modeled dust emission profile in FIR and millimeter wavelength range is deduced from the wings of some mid-infrared fundamental latticeresonances inside the silicate material, which is known to be the dominant constituent of this dust component. However recent astronomical observations have shown that the dust emission profile could be significantly more complicated than expected. In addition, spectroscopic studies in the laboratory on analogues of amorphous interstellar grains have revealed that additional processes can occur in that spectral range, which are strongly temperature-dependent. We propose a new model for far-infrared and millimeter dust emission which takes into account results from the solid state physics, used to interpret these laboratory data. This model explicitly incorporates the effect of the disorder in the internal structure of the dust grain. We show that this model can give a satisfactory interpretation for the astronomical observations. It opens new perspectives to derive some new dust characteristics from the shape of the dust emission spectrum. [ABSTRACT FROM AUTHOR]

Controlling the Mechanically Activated Self-propagating High-temperature Synthesis (MASHS) process is exceedingly important for production of MoSi2-based materials with a desired microstructure. Consequently, it seemed essential to carry out Time-Resolved X-ray Diffraction (TRXRD) experiments using an X-ray synchrotron beam (DM2, ESRF Grenoble) coupled with IR thermographic measurements to monitor in situ the structural and thermal evolutions taking place during SHS. The versatility of this technique and new possibilities offered by the design of new sample holders have already been proved. In addition, this work clearly shows that this equipment is perfectly adapted to investigating phase transitions occurring during the MASHS process in the Mo-Si system. [ABSTRACT FROM AUTHOR]

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 106 photons pixel−1 s−1. The pixel sizes are 0.33 mm × 0.33 mm for a total area of 68 mm × 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. [ABSTRACT FROM AUTHOR]

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 fulfill the needs of materials science scattering experiments. At the time, its prototype is build of eight modules of eight chips. The threshold calibration of ≈ 4 10´ pixels is discussed. Applications to powder diffraction or SAXS experiments prove that it allows to record high quality data. [ABSTRACT FROM AUTHOR]

Presents results obtained from a prototype photon counting detector with large dynamic range. Pixel size; Dynamic response range; Energy resolution; Small-angle X-ray scattering (SAXS) and diffraction patterns.

Monolayers of short chiral alcohols at the water surface provide a simple model for chiral interactions between molecules. This paper is focused on alcohols with two particular chain lengths, 2-tridecanol (2C13) and 2-tetradecanol (2C14). Thermodynamic and structural parameters were measured, varying the ratio of left and right enantiomers within monolayers. The evolution of melting temperatures and entropies is not consistent with the formation of a racemate. Grazing X-ray diffraction, revealing the molecular stacking, shows clearly that there is no chiral separation. In these two compounds molecules spontaneously self-assemble at the water surface as a solid solution. The chiral polar head-group is partially screened by the chain thermal disorder of the rotator phase. 2-tridecanol exhibits a hexagonal rotator phase stable in time and independent of temperature. Experiments performed close to the melting point show pre-transitional effects for mixtures different from 50/50. This broadening of the peak can be related to defects in 2D crystals, phenomena already observed for the melting of some 3D systems. [ABSTRACT FROM AUTHOR]

Presents a study which constructed a large surface semiconductor photon counting pixel detector. Creation of the first prototypes of the X-ray pixel detector; Electronic chip results; Prototype test results.