1. Institute of Nanostructured Materials (ISMN) National Research Council (CNR) Via P. Gobetti 101 Bologna 40121 Italy
2. CSEM Center Muttenz Tramstrasse 99 Muttenz CH‐4132 Switzerland
3. Plasmore s.r.l Viale Vittorio Emanuele II 4 Pavia 27100 Italy
4. Fraunhofer FEP Winterbergstraße 28 01277 Dresden Germany
5. Physics Department University of Pavia Via A. Bassi 6 Pavia 27100 Italy