[1] Univ Milano Bicocca, Dipartimento Sci Mat, Via R Cozzi 55, I-20125 Milan, Italy
[2] Ist Italiano Tecnol, Electron Microscopy Facil, Via Morego 30, IT-16163 Genoa, Italy
[3] Basque Ctr Mat Applicat & Nanostruct, BCMat, UPV EHU Sci Pk, Leioa 48940, Spain
[4] IMEM CNR Inst, Parco Area Sci 37-A, I-43124 Parma, Italy