Publications

Electrically-tunable positioning of topological defects in liquid crystals

Published in Nature Communications, 2020

Topological defects are a consequence of broken symmetry in ordered systems and are important for understanding a wide variety of phenomena in physics. In liquid crystals (LCs), defects exist as points of discontinuous order in the vector field that describes the average orientation of the molecules in space and are crucial for explaining the fundamental behaviour and properties of these mesophases. Recently, LC defects have also been explored from the perspective of technological applications including self-assembly of nanomaterials, optical-vortex generation and in tunable plasmonic metamaterials.

Here, we demonstrate the fabrication and stabilisation of electrically-tunable defects in an LC device using two-photon polymerisation and explore the dynamic behaviour of defects when confined by polymer structures laser-written in topologically discontinuous states. We anticipate that our defect fabrication technique will enable the realisation of tunable, 3D, reconfigurable LC templates towards nanoparticle self-assembly, tunable metamaterials and next-generation spatial light modulators for light-shaping.

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I have written a “Behind The Paper” post explaining topological defects in liquid crystals, which you can find here.

Sandford O’Neill, J. J., Salter, P. S., Booth, M. J., Elston, S. J., Morris, S. M., "Electrically-tunable positioning of topological defects in liquid crystals." Nature Communications, 11, 2203 (2020) https://doi.org/10.1038/s41467-020-16059-1

Robust measurement of flexoelectro-optic switching with different surface alignments

Published in Journal of Applied Physics, 2019

The alignment of chiral nematic liquid crystals in the so-called uniform lying helix geometry allows for the observation and exploitation of the flexoelectro-optic effect. However, high-quality uniform lying helix alignment is difficult to achieve reliably, and this can potentially impact the accuracy of the measurements made on the flexoelectro-optic switching behaviour. Here, we show that, using an appropriate method, it is possible to make measurements of the flexo-electric coefficients that are not substantially influenced by the alignment quality.

Sandford O’Neill, J. J., Fells, J. A. J., Welch, C., Mehl, G., Yip, W. C., Wilkinson, T. D., Booth, M. J., Elston, S. J., Morris, S. M., "Robust measurement of flexoelectro-optic switching with different surface alignments." Journal of Applied Physics, 125, 093104 (2019) http://dx.doi.org/10.1063/1.5086241

Read on Demand Images in Laser-Written Polymerizable Liquid Crystal Devices

Published in Advanced Optical Materials, 2018

Two‐photon laser writing is a powerful technique for creating intricate, high resolution features in polymerizable materials. Here, using a single‐step process to microfabricate polymer inclusions, the ability to generate read‐on‐demand images and identification codes in a liquid crystal (LC) device is demonstrated.

Tartan, C. C., Sandford O’Neill, J. J., Salter, P. S., Aplinc, J., Booth, M. J., Ravnik, M., Morris, S. M., Elston, S. J., "Read on Demand Images in Laser-Written Polymerizable Liquid Crystal Devices." Advanced Optical Materials, 6, 1800515 (2018) http://dx.doi.org/10.1002/adom.201800515