1. IFIMUP and IN – Institute of Nanotechnology, and Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre, 678, 4169-007 Porto, Portugal
2. INESC-MN and IN - Institute of Nanoscience and Nanotechnology, Rua Alves Redol, 9, 1000-029 Lisboa, Portugal