1. Szczecin University of Technology, Institute of Chemical and Environment Engineering, Pułaskiego 10, 70-322 Szczecin, Poland
2. Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warszawa, Poland
3. Center for Solid State Physics and New Materials, Institute of Physics, Pregrevica 118, 11080 Belgrade, Serbia