1. Department of Electrical and Computer Engineering University of California Los Angeles CA 90095 USA
2. National Nano Device Laboratories (NDL) Hsinchu 30078 Taiwan
3. Department of Materials Science and Engineering National Tsing Hua University Hsinchu 30043 Taiwan
4. Department of Electrophysics National Chiao Tung University Hsinchu 30010 Taiwan
5. Department of Physics National Taiwan University Taipei 10617 Taiwan
6. Department of Applied Physics National Pingtung University Pingtung 90044 Taiwan
7. Research Center for Applied Sciences Academia Sinica Taipei 11529 Taiwan
8. Department of Mechanical Engineering National Chiao Tung University Hsinchu 30010 Taiwan