1. Department of Electrical Engineering and Computer Sciences, UC Berkeley, Berkeley, California 94720, United States
2. The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Department of Physics, UC Berkeley, Berkeley, California 94720, United States
4. Department of Chemistry, UC Berkeley, Berkeley, California 94720, United States
5. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
6. Kavli Energy NanoSciences Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States