1. Department of Physics, Institute for Energy Technology, NO-2027 Kjeller, Norway
2. Department of Physics, University of Durham, Durham DH1 3LN, England
3. Department of Physics, University of Warwick, Coventry CV4 7AL, England
4. Departamento de Química, Universidade de Coimbra, PO-3004-535 Coimbra, Portugal
5. Departamento de Física, CICECO, Universidade de Aveiro, PO-3810-193 Aveiro, Portugal
6. Materials Science Centre, DSM Research, NL-6160 MD Geleen, The Netherlands
7. Department of Physics, FI-00014 University of Helsinki, Finland
8. Fachbereich Chemie, Bergische Universität Wuppertal, DE-42097 Wuppertal, Germany