1. Institute
of Physics, Academia Sinica, Taipei 11529, Taiwan
2. Danang
College of Technology, The University of Danang, Danang 59000, Vietnam
3. Institute
of Atomic and Molecular Science, Academia Sinica, Taipei 11529, Taiwan
4. Department
of Physics and Center for Nanotechnology, Chung Yuan Cristian University, Chungli 32023, Taiwan
5. Department
of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan