1. Physics and Chemistry of Nanostructures, Ghent University, Krijgslaan 281-S12, B-9000 Ghent, Belgium
2. Institute for Nuclear and Radiation Physics and INPAC, Celestijnenlaan 200D, K.U. Leuven, B-3001 Leuven, Belgium
3. Laboratory of Analytical Chemistry, Ghent University, Krijgslaan 281-S12, B-9000 Ghent, Belgium
4. NMR and Structure Analysis Unit, Ghent University, Krijgslaan 281-S4bis, B-9000 Ghent, Belgium
5. Institut d’Electronique, de Microélectronique et de Nanotechnologie, F-59652 Villeneuve d’Ascq Cedex, France