1. CNR - Istituto Officina dei Materiali (IOM), S.S. 14 km 163.5, Trieste I-34149, Italy
2. Department of Physics, University of Milan, Via Festa del Perdono 7, Milan 20122, Italy
3. Department of Physics, University of Trieste, Via Alfonso Valerio 2, Trieste 34127, Italy
4. Department of Engineering and Architecture, University of Trieste, Via Alfonso Valerio 2, Trieste 34127, Italy
5. Istituto dei Sistemi Complessi (ISC)-CNR, Piazzale Aldo Moro 5, Rome 00185, Italy