ship (ECF-2015-494) and from the Royal Society through a University Research Fellowship (UF160152). RAB acknowledges support from the EPSRC CDT in Nanoscience and Nanotechnology (NanoDTC), grant number EP/L015978/1. We acknowledge Diamond Light Source for provision of synchrotron beamtime (SM17271 and SM19371) and we would like to thank A. Smith and T. Snow for assistance in operating beamline I22. We thank T. Knowles and B. Mognetti for insightful discussions on this project.