1. Department of Materials Science and Engineering, University of California−Irvine, Irvine, California 92697, United States
2. State Key Laboratory of Surface Physics, Key Laboratory of Computational Physical Sciences and Department of Physics, Fudan University, Shanghai 200433, China
3. Irvine Materials Research Institute, University of California−Irvine, Irvine, California 92697, United States
4. Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14850, United States
5. Department of Physics and Astronomy, University of California−Irvine, Irvine, California 92697, United States