1. Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
2. Department of Physics and Institute for Accelerator Science, Kangwon National University, 1 Gangwondaehak-gil, Chuncheon-si, Gangwon-do 24341, Korea
3. Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
4. Department of Electrical Engineering, Columbia University, New York, New York 10027, United States
5. Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
6. Department of Materials Science and Engineering, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States