ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Two data sets containing altogether 131 Bragg intensities have been collected from a CaF2 crystal of 200 μm3 volume, which corresponds to a cube of about 6 μm edge length. The scattering power S of this crystal amounts to 1.3 × 1014. It is the smallest crystal ever used for an X-ray diffraction experiment. Crystal orientation and data collection were carried out at the storage ring DORIS II, HASYLAB, DESY, Hamburg, with the wavelength λ = 0.91 Å. For the first data set all reflections up to sin θ/λ = 0.58 Å-1 were collected, for the second only those reflections considered as observed by a prescan were measured up to sin θ/λ = 0.78 Å-1. The refinements, carried out as a function of the degree of polarization K, converged to Rw(F) = 0.005 for K = 0.93 and Rw(F) = 0.031 for K = 0.94 for the first and second data set, respectively. For comparison, a 90 μm sphere was investigated with synchrotron radiation [sin θ/λ ≤ 0.91 Å-1, Rw(F) = 0.020, K = 0.50] and with a normal X-ray tube [Mo Kα Rw(F) = 0.013]. The intensities are strongly affected by secondary extinction, in contrast to the 6 μm crystal. The following isotropic temperature factors were obtained for the 6 μm, 90 μm (synchrotron) and 90 μm (X-ray tube) data: B(Ca) = 0.38 (5), 0.64 (3), 0.610 (6); B(F) = 0.83 (4), 0.92 (3), 0.812 (8) Å2. The TDS correction increased only the temperature factors from the data set measured with the X-ray tube owing to the difference in FWHM (0.03° for synchrotron radiation, 0.210° for the X-ray tube).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S010876738500006X
