1. Department of Physics, Cornell University, Ithaca, New York 14853, USA
2. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
3. Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
4. School of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853, USA
5. Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright Patterson AFB, Ohio 45433, USA
6. Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA