Diamond’s Test Beamline B16 has overseen the birth of a new technique that reveals the behaviour of molecular bonds in anisotropic solids using polarised X-rays. The new technique, called X-ray Birefringence Imaging (XBI), works in a similar way to optical polarising microscopy. However, instead of observing visible light as it passes through an optically anisotropic material, XBI interrogates the spatial distribution and orientation of molecules within a given material.
Thanks to the versatility of B16 for performing novel experiments, scientists have for the first time been able to demonstrate the spatially resolved mapping of an X-ray birefringent material, building on their previous studies using narrowly focused X-ray beams. The large-area linearly polarised X-ray beam used to probe the utility of XBI was applied to a thiourea ‘host’ crystal containing various brominated guest molecules within its atomic-scale tunnels, which produced a number of snap-shots of the ordering and alignment of the guest C-Br bonds.
After establishing the technique through a detailed series of measurements of the well-characterised thiourea/dibromoalkane, the team went on to create a movie of the spontaneous formation of polarised domains in thiourea/cyclobromohexane upon cooling (see published paper's supplementary material movies S1-7).
This new ability to analyse the dynamics of chemical bond orientations in both crystalline and non-crystalline matter could shed light on important technologies such as catalysis and liquid crystals.
The star performer in the experiment was the B16 test beamline. B16 is an adaptable beamline for trialling new developments in optics and detector technology, and novel experimental techniques. Steve Collins, Principal Beamline Scientist on the neighbouring I16 beamline, who led the experimental set-up said “we were very pleased to be able to use B16 as the space and equipment allowed us to build our experiment precisely as we needed it. The bespoke beam specifications also gave us the ability to perform the full-field imaging whilst limiting radiation damage to the sample”.
The results from the experiment, published in Science, represent an important breakthrough in the ongoing collaboration between Cardiff University and Diamond, who together have been looking into the X-ray birefringence phenomenon in recent years. Professor Kenneth Harris, the principal investigator from Cardiff University, said “This is a very significant moment for us. Now that we have been able to demonstrate the spatially resolved imaging capabilities of X-ray birefringence, we can really start to further our understanding of anisotropic materials and their domain structures. Furthermore, there are really exciting prospects for exploiting the time-resolved capabilities of X-ray Birefringence Imaging in the future, allowing dynamic aspects of molecular orientational distributions in materials to be explored”.
The full-field imaging technique also opens up new avenues for studying dynamics on ultra-short timescales. Whist XBI has been used to capture entire images very quickly in one second intervals, the potential is now there for imaging ultra-fast molecular dynamics by capturing measurements in under 100fs with a single flash of an X-ray free-electron laser.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
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