1. Centre for Energy Research, Institute for Technical Physics and Material Science, Hungarian Academy of Sciences, MTA EK MFA, Konkoly-Thege M. u. 29-33, 1121 Budapest, Hungary
2. Institute for Electron Microscopy and Nanoanalysis and Graz Centre for Electron Microscopy, TU Graz, Steyrergasse 17, 8010 Graz, Austria
3. Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece