[1] NCSR Demokritos, Inst Mat Sci, Athens 15310, Greece
[2] Palacky Univ, Dept Phys Chem & Expt Phys, Olomouc 77146, Czech Republic
[3] Univ Ioannina, Dept Mat Sci & Engn, GR-45110 Ioannina, Greece
[4] Fdn Res & Technol Hellas, Inst Elect Struct & Laser, GR-71110 Iraklion, Crete, Greece
[5] Cornell Univ, Dept Mat Sci & Engn, Ithaca, NY 14853 USA