1. Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
2. Department of Applied Physics, Stanford University, Stanford, California 94305, United States
3. Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan
4. SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025,United States
5. Department of Chemistry, Stanford University, Stanford, California 94305, United States