1. CNR‐SPIN Salerno via Giovanni Paolo II n. 132 Fisciano 84084 Italy
2. Physics Department “E. R. Caianiello” University of Salerno and CNR‐SPIN Salerno via Giovanni Paolo II n. 132 Fisciano 84084 Italy
3. Department of Physical and Chemical Science University of L'Aquila and CNR‐SPIN L'Aquila via Vetoio, Coppito L'Aquila 67100 Italy
4. Department of Materials Science and Engineering Inha University 100 Inha‐ro Incheon 22212 Republic of Korea