1. Department of Physics, Stanford University, Stanford, California 94305, United States
2. Stanford Institute of Materials and Energy Sciences, SLAC National Laboratory, Menlo Park, California 94025, United States
3. Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California 94720, United States
4. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, 08193 Barcelona, Spain
5. Department of Applied Physics, Stanford University, Stanford, California 94305, United States
6. Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27606, United States
7. Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, California 94720, United States
8. Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, California 94720, United States
9. Departments of Materials Science and NanoEngineering, Chemistry, and Physics and Astronomy and the Rice Advanced Materials Institute, Rice University, Houston, Texas 77005, United States