1. Center for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway, FYSIKUM, AlbaNova, Stockholm University, S-10691 Stockholm, Sweden, and Department of Hydrocarbon Process Chemistry, SINTEF Materials and Chemistry, P.O. Box 124 Blindern, N-0314 Oslo, Norway