1. Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA
2. Department of Physics, University of California Berkeley, Berkeley, California 94720, USA
3. Department of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, California 94720, USA
4. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5. Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
6. Kavli Nanosciences Institute at Berkeley, Berkeley, California, 94720, USA