[1] Fdn Res & Technol Hellas, Inst Elect Struct & Laser, Iraklion 71110, Crete, Greece
[2] Univ Crete, Dept Mat Sci & Technol, Iraklion 71003, Crete, Greece
[3] Inst Educ Technol, Dept Sci, Iraklion 71004, Crete, Greece
[4] Iowa State Univ, Ames Lab, Ames, IA 50011 USA
[5] Iowa State Univ, Dept Phys & Astron, Ames, IA 50011 USA
[6] Univ Crete, Dept Phys, Iraklion 71003, Crete, Greece