1. Dipartimento di Fisica e Astronomia “Ettore Majorana,” Università di Catania 1 , Via S. Sofia 64, 95123 Catania, Italy
2. CNR-IMM 2 , Via S. Sofia 64, 95123 Catania, Italy
3. CNR-IMM 3 , Strada VIII n.5, 95121 Catania, Italy
4. Department of Chemical Sciences, University of Catania 4 , Viale Andrea Doria 6, 95123 Catania, Italy
5. Research Unit of the University of Catania, National Interuniversity Consortium of Materials Science and Technology (INSTM-UdR of Catania) 5 , Viale Andrea Doria 8 and Via S. Sofia 64, 95125 Catania, Italy