1. Department
of Materials Science and Engineering, University of Ioannina, GR-45110 Ioannina, Greece
2. Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, N. Plastira 100, GR-70013 Heraklion, Crete Greece
3. Materials
Science Department, University of Patras, Patras GR-26504, Greece