1. Istituto per lo Studio dei Materiali Nanostrutturati, CNR-ISMN, Via Gobetti 101, 40129 Bologna, Italy
2. Instituto de Ciencia Molecular, Universidad de Valencia, Catedrático José Beltrán Martínez n° 2, 46980 Paterna, Spain
3. Department of Electrical and Computer Engineering 9560, University of California Santa Barbara, Santa Barbara, California 93106, USA