1. Department of Materials and Mineral Resources Engineering, Institute of Mineral Resources Engineering, National Taipei University of Technology, Taipei 10608, Taiwan, R.O.C.
2. Division of Physics and Semiconductor Science, Dongguk University, Seoul 04620, Republic of Korea
3. Oak Ridge Institute for Science and Education, Durham, North Carolina 27708, United States
4. Department of Chemistry, Duke University, Durham, North Carolina 27708, United States