Novel technique for spatially resolved imaging of molecular bond orientations using X-ray birefringence: applications and developments
Birefringence has been observed in anisotropic materials transmitting linearly polarized X-ray beams tuned close to an absorption edge of a specific element in the material. Synchrotron bending magnets provide X-ray beams of sufficiently high brightness and cross section for spatially resolved measurements of birefringence. The recently developed X-ray Birefringence Imaging technique has been successfully applied for the first time  at the Diamond Light Source versatile Test Beamline B16. The orientational order of C–Br bonds of brominated “guest” molecules within crystalline “host” tunnel structures (thiourea or urea inclusion compounds) has been studied using linearly polarized incident X-rays close to the Br K-edge. Imaging of domain structures , changes in C–Br bond orientations associated with order-disorder phase transitions , and the effects of dynamic averaging of C–Br bond orientations  have been demonstrated. The setup uses a vertically deflecting high-resolution double-crystal monochromator upstream from the sample and a horizontally deflecting single-crystal polarization analyser downstream with a Bragg angle as close as possible to 45°. In this way, the rotation angle of the polarization of the beam transmitted through the sample is measured as in polarizing optical microscopy. The theoretical instrumental background is calculated and compared with experimental observations. The summary of recent results and some perspective developments are presented and discussed.
 Palmer, B. A., Edwards-Gau, G. R., Kariuki, B. M., Harris, K. D. M., Dolbnya, I. P. and Collins, S. P. (2014) Science 344, 1013-1016.
 Palmer, B. A., Edwards-Gau, G. R., Kariuki, B. M., Harris, K. D. M., Dolbnya, I. P., Collins, S. P. and Sutter, J. P. (2015) J. Phys. Chem. Lett 6, 561-567.