1. Institute of NanoEngineering and MicroSystems, National Tsing-Hua University, Hsinchu 30013, Taiwan
2. Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu 30013, Taiwan
3. Research Center for Applied Sciences, Academia Sinica, Nankang, Taipei 11529, Taiwan
4. Department of Physics, National Tsing-Hua University, Hsinchu 30013, Taiwan