Abstract--The crystal structure of single crystals of kaolinite from Keokuk, Iowa, was refined using data measured at the microfocus X-ray beamline at the ESRE Grenoble, France (X = 0.6883, T -room temperatu[e). The volume of the crystals was 8 and 0.8 txm 3, respectively. Unit-cell parameters are: a = 5.154(9) A, b = 8.942(4) A, c = 7.401(10) A, c~ ~ 91.69(9) ~ , 13 = 104.61(5) ~ "/ -89.82(4) ~ . Space group C1 is consistent with the observed data. All non-hydrogen atoms were independently refined with anisotropic displacement parameters. The positions and isotropic displacement parameters for the three interlayer H atoms were refined a/so. The position of the intralayer H was found by difference-Fourier methods, although refinement was not possible. Difference-Fourier maps suggested large anisotropic displacement vectors of this intralayer H, however, no evidence for a second maximum was found. The diffraction patterns show diffuse scattering in streaks parallel to [001]* through hkl reflections with hk 0, which is caused by stacking faults. No twinning was observed for either of the two crystals.
Wide-angle X-ray diffraction patterns of single spider-silk fibres of < 5 ~tm diameter can be obtained at a third-generation synchrotron-radiation source in a few seconds per pattern. This is sufficient to observe the strongest equatorial and first layer line reflections. For higher-resolution structural work, data have to be recorded with cryocooling techniques in order to maintain the crystallinity of the sample for several minutes.
This report discusses the properties of a 13-keV submicrometer x-ray beam exiting from a waveguide. Waveguides for this spectral regime can be constructed by enclosing a low-absorbing material between highly absorbant metals. Best performance is found for about 0.1 μm guiding layer thickness. Measurements of the photon beam size close to the exit and of the intensity distribution far from the exit will be presented. From these data one derives a beam size at the exit which is identical to the guiding layer thickness. This number being in the submicrometer range offers interesting perspectives for microscopy experiments in the hard x-ray range.
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