1. IESL-FORTH, N. Plastira 100, 70013, Heraklion, Crete, Greece
2. Department of Materials Science and Technology, University of Crete, Heraklion, Crete, Greece
3. Department of Physics, University of Crete, Heraklion, Crete, Greece
4. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia