1. Department of Materials Engineering and Industrial Technologies; University of Trento; Via Mesiano 77 38050 Povo Trento Italy
2. Leitat Technological Center; C/ de la Innovació 2 08225 Terrassa (Barcelona) Spain
3. Laboratori Nazionali di Legnaro; Istituto Nazionale di Fisica Nucleare; Viale dell'Universita' 2 35020 Legnaro Padua Italy
4. Department of Physics and Astronomy G. Galilei; University of Padua; Via Marzolo 8 35131 Padua Italy