1. Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
2. Kubos Semiconductors Ltd, Future Business Centre, Kings Hedges Road, Cambridge CB4 2HY, United Kingdom
3. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, Jülich 52425, Germany
4. Centre for High Frequency Engineering, University of Cardiff, Queen's Building, Cardiff CF24 3AA, United Kingdom