1. Material
Sciences and Engineering, National Tsing-Hua University, Hsinchu, 30013, Taiwan
2. Department
of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, United States
3. Center
for Nanochemistry, Beijing National Laboratory for Molecular Sciences,
Key Laboratory for the Physics and Chemistry of Nanodevices, State
Key Laboratory for Structural Chemistry of Unstable and Stable Species,
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China