1. MIND, Department of Electronic and Biomedical Engineering, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Spain
2. Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Av. Diagonal 645, E-08028 Barcelona, Spain
3. Catalonia Institute for Energy Research (IREC), Jardins de les Dones de Negre 1, 2 pl., E-08930 Sant Adrià del Besòs (Barcelona), Spain
4. Laboratory for Nanotechnology, IMTEK, Faculty of Engineering, University of Freiburg, Georges-Köhler-Allee 103, D-79110 Freiburg, Germany
5. Centro de Investigación en Materiales Avanzados S.C. (CIMAV), Unidad Monterrey–PIIT, Apodaca, NL M-66628, Mexico