1. Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, California 92093, USA
2. Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
3. HRL Laboratories, 3011 Malibu Canyon Road, Malibu, California 90265, USA
4. Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095, USA
5. Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
6. Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
7. Materials Science and Engineering Program, University of California San Diego, La Jolla, California 92093, USA
8. Department of NanoEngineering, University of California San Diego, La Jolla, California 92093, USA