1. Division of Optical Spectroscopy, Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okolna Str. 2, 50-422 Wroclaw, Poland
2. Graphene Energy Ltd, Curie-Sklodowskiej Str. 55/61, 50-369 Wroclaw, Poland
3. Department of Functional Surfaces, Helmholtz-Zentrum Hereon, Max-Planck-Straße 1, 21502 Geesthacht, Germany
4. Department of Materials and Ceramic Engineering, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
5. Faculty of Physics, University of Belgrade, Studentski trg 12, 11001 Belgrade, Serbia