1. Department of Physics, Informatics and Mathematics, University of Modena and Reggio Emilia, Via Campi 213/a, 42125 Modena, Italy
2. Istituto di Istruzione Superiore Paradisi, V.le Resistenza 700, 41058 Vignola, Modena
3. CNR-NANO S3, Istitute of Nanoscience, Via Campi 213/a, 41125 Modena, Italy