1. Dipartimento di Scienze, Università Roma Tre, via della Vasca Navale, 84, 00146 Roma, Italy
2. CNR-Istituto di Struttura delle Materia, c/o Dipartimento di Scienze, Università Roma Tre, via della Vasca Navale, 84, 00146 Roma, Italy
3. CNR-Institute of Nanotechnology, c/o Physics Department, “Sapienza” University, Piazzale Aldo Moro 5, 00185 Roma, Italy
4. Electrical Engineering Division, Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, CB3 0FA Cambridge, United Kingdom
5. Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan
6. CNR-ISOF via Gobetti 101, 40129 Bologna, Italy