1. Université Montpellier 2, Laboratoire Charles Coulomb UMR 5221, F-34095 Montpellier, France
2. CNRS, Laboratoire Charles Coulomb UMR 5221, F-34095 Montpellier, France
3. Faculty of Physics, Southern Federal University, Rostov-on-Don, Russia
4. Laboratory of Carbon Nanomaterials, Institute of Materials Science, Vietnamese Academy of Science and Technology, Hanoi, Vietnam
5. Laboratorio de Microscopias Avanzadas (LMA), Instituto de Nanociencia de Aragon (INA), Universidad de Zaragoza, 50018 Zaragoza, Spain
6. Laboratoire d’Etude des Microstructures, ONERA-CNRS, 92322 Chatillon, France
7. Faculty of Physics, University of Sofia, BG-1164 Sofia, Bulgaria