1. Section of Condensed Matter Physics, Department of Physics, National and Kapodistrian University of Athens, University Campus, Zografou, Athens 15784, Greece
2. Institute of Nanoscience and Nanotechnology, National Center for Scientific Research “Demokritos”, Agia Paraskevi, Athens 15341, Greece
3. Laboratory of Analytical Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, University Campus, Zografou, Athens 15771, Greece
4. Department of Physics, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Athens 15780, Greece