1. Department of Chemistry and Biochemistry and The California NanoSystems Institute, University of California, Los Angeles, California 90095-1569, United States
2. The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Department of Materials Science & Engineering, Cornell University, Ithaca, New York 14853, United States
4. Department of Materials Science & Engineering, University of California, Los Angeles, California 90095, United States