1. Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki 00014, Finland
2. Department of Physics, Institute for Energy Technology, P.O. Box 40, N-2027 Kjeller, Norway
3. Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway
4. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan