1. Department of Materials Science & Engineering University of Ioannina 45110 Ioannina Greece
2. Zernike Institute for Advanced Materials University of Groningen Nijenborgh 4 9747 AG Groningen The Netherlands
3. current address: Department of Materials Science and Engineering Cornell University Ithaca NY 14853 USA
4. current address: Department of Materials National Graphene Institute Henry Royce Institute University of Manchester Oxford Road Manchester M13 9PL United Kingdom
5. current address: Department of Materials Science University of Patras GR-26504 Patras Greece
6. Institute of Nanoscience and Nanotechnology NCSR “DEMOKRITOS” 15310 Ag. Paraskevi-Attikis Athens Greece
7. Department of Physics University of Ioannina 45110 Ioannina Greece
8. Nano-Bio Electron Microscopy Research Group Korea Basic Science Institute Yuseong-gu Daejeon Republic of Korea
9. Department of Chemical Engineering Khalifa University of Science and Technology The Petroleum Institute PO Box 2533 Abu Dhabi United Arab Emirates