1. Laboratory of Nanomaterials and Devices (SSPT-PROMAS-NANO), ENEA—C.R. Portici, Piazzale Enrico Fermi 1, I-80055 Portici, Napoli, Italy
2. National Research Council, Institute for Applied Sciences and Intelligent Systems “E. Caianiello” (CNR-ISASI), Via Campi Flegrei 34, I-80078 Pozzuoli, Napoli, Italy