1. Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, R.O.C.
2. Nano Science and Technology Program, Taiwan International Graduate Program, Academia Sinica, Taipei 11529, Taiwan, R.O.C.
3. Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan, R.O.C.
4. Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan, R.O.C.