1. Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, United States
2. Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, United States
3. Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan
4. Department of Chemistry, University of Texas at Dallas, Richardson, Texas 75080, United States
5. Institute of Atomic and Molecular Science, Academic Sinica, Taipei 10617, Taiwan