Synchrotron X-ray diffraction on a CaF₂ microcrystal with 2.2 cubic micrometres volume

The photon flux generated by the six-pole wiggler at CHESS combined with a focusing mirror and a focusing monochromator allowed diffraction experiments at 1.56 Å, wavelength with a 2.2 (5) μm³ CaF₂ single crystal. The crystal was oriented by means of a multiwire proportional area counter. Reflection profiles and Bragg intensities were collected with a scintillation counter. The Bragg intensities were used for a structure refinement. The results demonstrate that crystals composed of light elements with volumes down to only 0.5 μm³ can be mounted and used for single-crystal X-ray diffraction experiments. Until now such crystals have been considered as powder grains. Besides the possibility of applying single-crystal methods to materials of which larger crystals are not available the essentially extinction-free data from microcrystals allow a high- precision determination of electron densities and vibrational amplitudes.