1. Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
2. Department of Physics, Stanford University, Stanford, CA 94305, USA.
3. Stanford Institute for Materials and Energy Sciences, Stanford Linear Accelerator Center National Accelerator Laboratory, Menlo Park, CA 94025, USA.
4. Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA.
5. Department of Applied Physics, Stanford University, Stanford, CA 94305, USA.
6. Precourt Institute for Energy, Stanford University, Stanford, CA 94305, USA.