1. Department of Physics, Stanford University; Stanford CA 94305 USA
2. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory; Menlo Park CA 94025 USA
3. School of Electrical and Computer Engineering, Cornell University; Ithaca NY 14853 USA
4. Department of Applied Physics Stanford University; Stanford CA 94305 USA
5. Department of Advanced Materials Science, The University of Tokyo; Kashiwa Chiba 277-8561 Japan
6. Department of Materials Engineering, The University of Tokyo; Bunkyo Tokyo 113-8656 Japan
7. H. H. Wills Physics Laboratory, University of Bristol; Tyndall Avenue Bristol BS8 1TL UK
8. Stanford Nano Shared Facilities, Stanford University; Stanford CA 94305 USA
9. School of Applied and Engineering Physics, Cornell University; Ithaca NY 14853 USA
10. Kavli Institute at Cornell for Nanoscale Science, Cornell University; Ithaca NY 14853 USA