1. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan R.O.C
2. Department of Physics, School of Sciences and Humanities, SR University, Warangal 506371, India
3. Department of Materials Science and Engineering, National Tsing Hua University, No. 101 Section 2, Kuang Fu Road, Hsinchu City 300, Taiwan R.O.C
4. Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 106, Taiwan, R.O.C.
5. Department of Physics, National Tsing Hua University, Hsinchu City 300, Taiwan R.O.C
6. Research Centre for Applied Science, Academia Sinica, Taipei 115, Taiwan R.O.C