1. Department of Chemistry, University of California Berkeley, Berkeley, California94720, United States
2. Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
3. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
4. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
5. Department of Physics, University of California Berkeley, Berkeley, California94720, United States
6. Kavli Energy NanoSciences Institute, Berkeley, California94720, United States