1. Department of Physics, National Taiwan University, Sec. 4, Roosevelt Road, Taipei 106, Taiwan, ROC
2. Research Center for Applied Science, Academia Sinica, Taipei 115, Taiwan, ROC
3. Nano Science and Technology, Taiwan International Graduate Program, Academia Sinica and National Taiwan University, Taipei 106, Taiwan, ROC
4. Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC
5. Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC
6. College of Engineering, Chang Gung University, Taoyuan 320-338, Taiwan, ROC