1. National Council of Research Institute for Microelectronic and Microsystems (CNR-IMM) Z.I. VIII Strada 5 95121 Catania Italy
2. Department of Physics and Astronomy University of Catania Via Santa Sofia 64 95123 Catania Italy
3. LSI CEA/DRF/IRAMIS CNRS Ecole Polytechnique Institut Polytechnique de Paris 91120 Palaiseau France
4. Department of Physics and Chemistry Emilio Segrè University of Palermo Via Archirafi 36 90123 Palermo Italy
5. ATeN Center University of Palermo Viale delle Scienze Ed. 18 90128 Palermo Italy