1. Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan
3. Department of Physics, National Taiwan University, Taipei 106, Taiwan
4. Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
5. Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
6. Institute of Physics, Academia Sinica, Taipei 106, Taiwan
7. Center for Emergent Functional Matter Science, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
8. International College of Semiconductor Technology, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan