1. Contribution from the Laboratory of Physical Chemistry and Electrochemistry, Helsinki University of Technology, P.O. Box 6100, FIN-02015 HUT, Finland, Condensed Matter and Interfaces, Debye Institute, University of Utrecht, P.O. Box 80000, 3508 TA Utrecht, The Netherlands, VTT Processes, Aerosol Technology Group, P.O. Box 1602, FIN-02044 VTT, Espoo, Finland, and Center for New Materials, Helsinki University of Technology, P.O. Box 1602 FIN-02044 VTT, Espoo, Finland