1. Department of Physics, NIS Interdepartmental Centre, University of Torino and Italian Institute of Nuclear Physics, via Giuria 1, 10125 Torino, Italy
2. Department of Drug and Science Technology, NIS Interdepartmental Centre, University of Torino, Corso Raffaello 30, 10125 Torino, Italy
3. Department of Chemistry, NIS Interdepartmental Centre, University of Torino, via Giuria 7, 10125 Torino, Italy
4. Institute of Electron Devices and Circuits, University of Ulm, 89069 Ulm, Germany