1. Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California 94720, United States
2. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Department of Physics, Nanoscience Center, University of Jyväskylä, FI 40014 Jyväskylä, Finland
4. Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI 40014 Jyväskylä, Finland
5. Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States