1. Institute of Experimental Physics, University of Wrocław, pl. M. Borna 9, 50-204 Wrocław, Poland
2. Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
3. Institute of Low Temperature and Structure Research of the Polish Academy of Sciences Okólna 2, 50-422 Wrocław, Poland
4. Department of Physics, Opole University of Technology, Ozimska 75, 45-271 Opole, Poland