1. Department of Chemistry and Chemical Technologies, University of Calabria, 87036 Arcavacata di Rende (CS), Italy;
2. CNR-ISMN, National Council of Research, Institute for the Study of Nanostructured Materials, Via Salaria km 29.300, Monterotondo Stazione (RM), Italy;
3. Department of Physics and CNR-Nanotec, University of Calabria, via Bucci 31C, 87036 Rende (CS), Italy