1. Department of Chemistry, Stanford University, Stanford, California 94305, United States
2. Department of Physics, University of California Berkeley, Berkeley, California 94720, United States
3. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
4. Kavli Energy NanoScience Institute at Berkeley, Berkeley, California 94720, United States
5. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States