1. Department
of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan, Republic of China
2. National Nano Device Laboratories, No. 26, Prosperity Road 1, Hsinchu 30078, Taiwan, Republic of China
3. Department
of Electrical Engineering, University of California, Los Angeles, California 90095, United States
4. Electrical
Engineering and Computer Sciences, University of California, Berkeley, California 94720, United States
5. School
of Material Science and Engineering, State Key Laboratory of Advanced
Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou City 730050, Gansu, P.R. China