1. Institute of Physics, Ecole Polytechnique Fédérale de Lausanne, Station 3, 1015 Lausanne, Switzerland
2. Nanoscale Materials Science, Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
3. Center for Quantum Nanoscience, Institute for Basic Science (IBS), Seoul 03760, Republic of Korea
4. Department of Physics, Ewha Womans University, Seoul 03760, Republic of Korea
5. Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
6. Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland