1. Department für Chemie, Universität zu Köln, Luxemburger Strasse 116, Köln 50939, Germany
2. Institut für Angewandte Physik der Universität Bonn, Wegeler Strasse 8, Bonn 53115, Germany
3. II. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
4. Department of Chemistry, University of California at Berkeley, Tan Hall, Berkeley, California 94720, United States
5. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
6. Kavli Energy NanoSciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States