1. Department of Physics, National Taiwan University 1 , Taipei 10617, Taiwan
2. Nanoscience and Technology Program, Taiwan International Graduate Program 2 , Academia Sinica, Taipei 115201, Taiwan
3. Department of Optoelectronics and Materials Technology, National Taiwan Ocean University 3 , Keelung City 202301, Taiwan
4. 4 Center for Emerging Material and Advanced Devices, National Taiwan University, Taipei 10617, Taiwan