1. Faculty of Physics, University of Bialystok, 15-245 Bialystok, Poland
2. Faculty of Physics and Applied Computer Science, AGH University of Krakow, 30-059 Kraków, Poland
3. Academic Centre for Materials and Nanotechnology, AGH University of Krakow, 30-059 Kraków, Poland
4. Helmholtz Centre Potsdam, Telegrafenberg, D-14473 Potsdam, Germany