1. Department of Physics; Columbia University; New York NY 10027 USA
2. Department of Chemistry; Columbia University; New York NY 10027 USA
3. Energy Frontier Research Center (EFRC); Columbia University; New York NY 10027 USA
4. School of Engineering and Applied Sciences and Department of Physics; Harvard University; Cambridge MA 02138
5. Center for Functional Nanomaterials; Brookhaven National Laboratory; Upton NY 11973 USA
6. Department of Electrical Engineering; Columbia University; New York NY 10027 USA
7. Advanced Materials Laboratory; National Institute for Materials Science; 1-1 Namiki Tsukuba 305-0044 Japan
8. Department of Mechanical Engineering; Columbia University; New York NY 10027 USA