[1] Univ Torino, Interdept Ctr NIS, Dept Phys, Via P Giuria 1, I-10125 Turin, Italy
[2] Univ Torino, Dept Chem, Interdept Ctr NIS, Via P Giuria 7, I-10125 Turin, Italy
[3] Univ Torino, INSTM Ctr Riferimento, Via P Giuria 7, I-10125 Turin, Italy
[4] Univ Rennes, CNRS, UMR 6226, ISCR, F-35000 Rennes, France
[5] Nanofacil Piemonte INRiM Ist Nazl Ric Metrol, Str Cacce 91, I-10135 Turin, Italy