1. Institute
of Nanoscience and Nanotechnology, National Center for Scientific Research Demokritos, Agia Paraskevi, Attiki, 15310 Athens, Greece
2. School
of Applied Mathematical and Physical Sciences, National Technical University of Athens, Zografou Campus, Athens 15780, Greece
3. Advanced
Technology Research and Application Center, Selcuk University, 42250 Selcuklu, Konya, Turkey
4. Department
of Natural Sciences, University of Chester, Thornton Science Park, CH2 4NU Chester, U.K.
5. Cavendish
Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom
6. Solid
State Physics Section, Physics Department, National and Kapodistrian University of Athens, Panepistimioupolis, 15784 Zografos, Athens, Greece