1. Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
2. Institute of Physics and Astronomy, University of Potsdam, Potsdam-Golm, Germany
3. Department of Physics, University of Bologna, Bologna, Italy
4. Polyera Corporation, Skokie, Illinois 60077, United States
5. Stanford Synchrotron Radiation Lightsource, Menlo Park, California 94025, United States