1. School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, United States
2. Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, United States
3. Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
4. Department of Materials Science and Engineering, National Chung Hsing University, Taichung 40227, Taiwan
5. School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, United States