1. Materials and Nano Physics, KTH Royal Institute of Technology, SE-164 40 Kista, Sweden
2. Department of Physics and Competence Centre for Catalysis, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
3. Department of Chemistry and Material Science (School of Chemical Engineering) and Department of Applied Physics (School of Science), Aalto University, 02150 Espoo, Finland