1. Laboratory
of Physical Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), FIN-00014 University of Helsinki, Finland
2. Department
of Physics, University of Helsinki, P.O. Box 64 (Gustaff Hällströmin
katu 2a), FIN-00014 University of Helsinki, Finland
3. Tianjin
International Center of Nanoparticles and Nanosystems, Tianjin University, 92 Weijin Road, Nankai district, Tianjin 300072, P. R. China
4. Department
of Physics, University of Gothenburg, 41296 Gothenburg, Sweden