1. Istituto di Chimica della Materia Condensata e delle Tecnologie per l’Energia, ICMATE, CNR, C.so Stati Uniti 4, 35127 Padova, Italy
2. Physics Department, University of Oviedo, 33007 Oviedo, Spain
3. Institute of Nanotechnology, CNR-NANOTEC, via Orabona 4, 70126 Bari, Italy