1. Energy Frontier Research Center, Columbia University, New York, New York 10027, United
States
2. Stanford Synchrotron Radiation Lightsource, Stanford Linear Accelerator Center,
Menlo Park, California 94025, United States
3. Department of Chemistry, Columbia University, New York, New York 10027, United
States
4. S3 Center, CNR-Nanoscience Institute, I-41125 Modena, Italy
5. Department of Physics, Columbia University, New York, New York 10027, United
States
6. Department of Physics
and Graphene
Research Institute, Sejong University,
Seoul 143-747, Korea
7. Department of Physics, Stockholm University, S-106 91 Stockholm, Sweden
8. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973-5000,
United States