1. Department of Physics “E.R. Caianiello”, University of Salerno, Via Giovanni Paolo II 132, 84084 Fisciano, SA, Italy
2. CNR-SPIN Salerno, Via Giovanni Paolo II 132, 84084 Fisciano, SA, Italy
3. NANO_MATES Research Centre, University of Salerno, Via Giovanni Paolo II 132, 84084 Fisciano, SA, Italy