1. Department of Physics and Chemistry Emilio Segrè, University of Palermo 1 , Via Archirafi 36, 90123 Palermo, Italy
2. LSI, CEA/DRF/IRAMIS, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris 2 , 91120 Palaiseau, France
3. Laboratoire Hubert Curien 3 , 18 rue du Professeur Lauras, 42000 Saint-Etienne, France
4. STMicroelectronics 4 , Stradale Primosole, 95121 Catania, Italy
5. ATeN Center, University of Palermo 5 , Viale delle Scienze Ed. 18, 90128 Palermo, Italy