1. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain
2. Karlsruhe Institute of Technology (KIT), Institute of Microstructure Technology, D-76344 Eggenstein Leopoldshafen, Germany
3. INL—International Iberian Nanotechnology Laboratory, Avenida Mestre José Veiga, 4715-330 Braga, Portugal
4. ICREA (Institució Catalana de Recerca i Estudis Avançats), 08010 Barcelona, Spain