1. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, 37831 Tennessee, United States
2. Birck Nanotechnology Center and School of Electrical and Computer Engineering, Purdue University, West Lafayette, 47907 Indiana, United States
3. Department of Physics and Astronomy, Vanderbilt University, Nashville, 37235 Tennessee, United States
4. University of Chinese Academy of Sciences & Institute of Physics, Chinese Academy of Sciences, 100190 Beijing, China
5. Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, 37235 Tennessee, United States
6. Department of Materials Science and Engineering, North Carolina State University, Raleigh, 27695-7907 North Carolina, United States