Strain Mapping by Coherent X-Ray Diffraction
Ian Robinson
University College London and Diamond Light Source
Our latest direction in three dimensional imaging by inversion of Coherent X-ray Diffraction (CXD) patterns involves its extension to complex density functions of the interiors of nanocrystals. An ideal crystal, whatever its shape, when illuminated with an ideal plane wave must give rise to a diffraction pattern that is symmetric about the exact Bragg point at the centre of the intensity distribution. This is rarely observed in practice, since imperfect beams can easily contribute to the symmetry breaking. Our most careful measurements on lead nanocrystals grown in-situ in the 34-ID-C beamline at APS, were still found to be weakly non-centrosymmetric. This showed as missing density in the 3D images obtained by phase retrieval and inversion. However when the image function was allowed to become complex, the missing density was recovered, but only because a significant phase structure was introduced.
We interpret the imaginary part of the image as a projection of deformation fields that are attributed to the conditions of growth of the crystal. This talk will provide details of these results and consider some future applications of the CXD method which are highly attractive with the high brilliance of an ERL source.
