1. Area Science Park, Basovizza S.S. 14 Km 163.5, 34149 Trieste, Italy
2. Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milano, Italy
3. Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, Via Rubattino 81, 20134 Milan, Italy
4. CNR-IOM, Consiglio Nazionale delle Ricerche Istituto Officina dei Materiali, Trieste, Italy
5. School of Physics, CRANN & AMBER Research Centres, Trinity College Dublin, Dublin D02, Ireland
6. Catalan Institute of Nanoscience and Nanotechnology ICN2 UAB Campus, Bellaterra (Barcelona) 08193, Spain
7. TU Eindhoven, Department of Applied Physics, Den Dolech 2, 5612 AZ, Eindhoven, The Netherlands