Orientational ordering in the chiral smectic-C*FI2 liquid crystal phase determined by resonant polarized x-ray diffraction.

High-resolution resonant polarized x-ray diffraction experiments near the sulfur K edge have been performed on free-standing liquid crystal films exhibiting the chiral smectic-C*FI2 phase. It is widely accepted that this phase has a four-layer repeat unit, but the internal structure of the repeat unit remains controversial. We report different resolved features of the resonant x-ray diffraction peaks associated with the smectic-C*FI2 phase that unambiguously demonstrate that the four-layer repeat unit is locally biaxial about the layer normal and that the measured angle, describing the biaxiality, is in good agreement with optical measurements.

Reconstruction of the shapes of gold nanocrystals using coherent x-ray diffraction.

Inverse problems arise frequently in physics: The magnitude of the Fourier transform of some function is measurable, but not its phase. The "phase problem" in crystallography arises because the number of discrete measurements (Bragg peak intensities) is only half the number of unknowns (electron density points in space). Sayre first proposed that oversampling of diffraction data should allow a solution, and this has recently been demonstrated. Here we report the successful phasing of an oversampled hard x-ray diffraction pattern measured from a single nanocrystal of gold.

Asymmetric Fraunhofer diffraction from roller-blade slits.

X-ray diffraction experiments under coherent conditions have been made possible by the development of new sources of synchrotron radiation, but make tough demands on the experimental apparatus. Here we describe the design and initial testing of a precision aperture that uses polished molybdenum rods as the slit blades. The device has an inherent asymmetry which is accurately accounted for by a simple modification to the Fraunhofer diffraction function.