1. Department of Earth Sciences, University of Cambridge, CB2 3EQ Cambridge, United Kingdom, Faculty of Physics, Vilnius University, Sauletekio Str. 9, LT-10222 Vilnius, Lithuania, Semiconductor Physics Institute, A. Gostauto str. 11, LT-01108 Vilnius, Lithuania, J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia, Institute of Physics, AS CR, Cukrovarnicka 10, 16253 Prague, Czech Republic, Department of Ceramics and Glass Engineering & CICECO, University of Aveiro, 3810-193 Aveiro, Portugal