1. Department of Physics, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä, Finland, Catalysis Research Center, Hokkaido University, Nishi 10, Kita 21, Sapporo 001-0021, Japan, Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä, Finland, and Department of Chemistry, Kansas State University, Manhattan, Kansas 66506