1. Department of Physics "E. Pancini", University of Naples Federico II, Via Cintia 26, 80126, Naples, Italy
2. Institute for Polymers, Composites and Biomaterials, National Research Council (CNR-IPCB), P. le Fermi, 1, 80055 Portici, Naples, Italy
3. CNR-SPIN c/o Department of Physics “E. Pancini”, Piazzale V. Tecchio 80, 80125, Naples, Italy
4. Faculty of Physics and Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, Duisburg 47057, Germany