1. Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
2. Ernst Ruska–Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich, Germany.
3. School of GeoSciences, University of Edinburgh, The King’s Buildings, West Mains Road, Edinburgh EH9 3JW, UK.
4. Department of Mechanical, Materials and Manufacturing Engineering, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK.