1. Department of Applied Physics, Stanford University, Stanford, CA 94305, USA.
2. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA.
3. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
4. Department of Physics, Stanford University, Stanford, CA 94305, USA.
5. Stanford Nano Shared Facilities, Stanford, CA 94305, USA.
6. Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA.