1. Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, California 91125, United States
2. Department of Medical Engineering, California Institute of Technology, Pasadena, California 91125, United States
3. Department of Electron Microscopy Development and Application, Division of Platform Technology for Advanced Materials, Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu 31057, Taiwan
4. Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu 31057, Taiwan
5. Department of Electrical Engineering, California Institute of Technology, Pasadena, California 91125, United States
6. Department of Physics, California Institute of Technology, Pasadena, California 91125, United States
7. Department of Physics, National Taiwan Normal University, Taipei City 106, Taiwan