1. Department of Physics, Stockholm University, AlbaNova University Center, S-106 91 Stockholm, Sweden
2. Institute of Physics, Jagiellonian University, ul. Reymonta 4, PL-30-059 Krakow, Poland
3. Faculty of Mathematics and Computer Science, University of Warmia and Mazury in Olsztyn, Sloneczna 54, Olsztyn PL-10710, Poland
4. Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden