1. Interdisciplinary Nanoscience Center (iNANO) and Danish National Research Foundation: Danish-Chinese Centre for Self-Assembly and Function of Molecular Nanostructures on Surfaces, 8000 Aarhus C, Denmark
2. Institute of Physics, The Chinese Academy of Sciences, Beijing 100190, China
3. Department of Chemistry, Aarhus University, 8000 Aarhus C, Denmark
4. Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark