1. Department
of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
2. Institut
für Mikro- und Nanostrukturforschung, Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstrasse 6, 91058 Erlangen, Germany
3. Stanford
Nano Shared Facilities, Stanford University, Stanford, California 94305, United States
4. Stanford
Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo
Park, California 94025, United States