1. LENS/MIND, Department of Electronics and Biomedical Engineering, Universitat de Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain
2. Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain
3. Centres Científics i Tecnològics de la Universitat de Barcelona. Solé i Sabaris, 1-3, 08028 Barcelona, Spain
4. NanoMEGAS SPRL, Blvd Edmond Machtens 79, B-1080 Brussels, Belgium
5. Microelectronics Research Group (MRG), IESL, FORTH, P.O. Box 1385, 71110 Heraklion, Greece
6. Department of Physics, University of Crete, 71203 Heraklion, Greece