1. Advanced Microscopy Laboratory, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin , Dublin D02 DA31 , Ireland
2. School of Physics, Trinity College Dublin , Dublin D02 E8C0 , Ireland
3. Centre for Doctoral Training in the Advanced Characterisation of Materials, AMBER Centre, Trinity College Dublin , Dublin D02 W9K7 , Ireland
4. Department of Physics, University of Warwick , Coventry CV4 7AL , UK
5. Advanced Materials Manufacturing Centre (AMMC), Warwick Manufacturing Group (WMG), University of Warwick , Coventry CV4 7AL , UK