1. Department
of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
2. Department
of Materials Science and Engineering and California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
3. Stanford
Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo
Park, California 94025, United States