1. Department of Electrical Engineering, Columbia University, New York, NY 10027, USA.
2. Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.
3. School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA.
4. Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611, USA.
5. Department of Chemistry, Columbia University, New York, NY 10027, USA.
6. National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
7. Department of Physics, Columbia University, New York, NY 10027, USA.
8. Department of Physics, The City College of New York, New York, NY 10031, USA.