1. Section of Condensed Matter Physics, Department of Physics, National and Kapodistrian University of Athens, Panepistimiopolis Zografos, Athens 157 84, Greece
2. Faculty of Engineering, Environment and Computing, Coventry University, Priory Street, Coventry CV1 5FB, United Kingdom
3. Department of Materials, Imperial College, London SW7 2AZ, United Kingdom
4. Department of Electrical and Computer Engineering, University of Thessaly, 38221 Volos, Greece