1. Department of Microtechnology and Nanoscience, Chalmers University of Technology, Kemivägen 9, S-41296 Göteborg, Sweden, Service de Chimie des Matériaux Nouveaux, Université de Mons, Place du Parc 20, B-7000 Mons, Belgium, and Nano-Science Center & Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark