1. Institute of Physics, University of Tartu, W.Ostwaldi 1, 50411 Tartu, Estonia
2. Department of Solid State Physics, Ångström Laboratory, Uppsala University, Box 35, SE-75103 Uppsala, Sweden
3. Department of Molecular Science, BioCenter, Swedish University of Agricultural Sciences, Box 7015, 75007 Uppsala, Sweden
4. Applied Physical Chemistry, KTH Royal Institute of Technology, Teknikringen 30, SE-100 44 Stockholm, Sweden
5. Institute of Molecular and Cell Biology, University of Tartu, Riia 23, 51010 Tartu, Estonia