1. Department of Chemistry, Columbia University, New York, New York 10027, United States
2. Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
3. Columbia
Nano Initiative, Columbia University, New York, New York 10027, United States
4. Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
5. Department of Electrical and Systems Engineering,
Department of Materials Science and Engineering, and Department of
Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States