1. Nanoscience and Materials Department, Istituto Nazionale di Ricerca Metrologica INRIM, 10135 Torino, Italy
2. Institute of Physics, P.J. Šafárik University, 04022 Košice, Slovakia
3. Laboratory of Inorganic Materials, CERTH, 57001 Thermi-Thessaloniki, Greece
4. Energy Department, Politecnico di Torino, 10129 Torino, Italy
5. Department of Chemical Engineering, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece