1. Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
2. Department of Chemical Engineering, SUNCAT Center for Surface Science and Catalysis, Stanford University, 443 Via Ortega, Stanford, California 94035, United States
3. SUNCAT Center for Surface Science and Catalysis, SLAC National Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States