1. Department
of Physics and Materials Science, City University of Hong Kong, 83 Tat
Chee Avenue, Hong Kong SAR, China
2. State
Key Laboratory of Silicon Materials, School of Materials Science and
Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
3. Department
of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong
SAR, China
4. City Universities of Hong Kong Shenzhen Research Institute, Shenzhen, Guangdong 518057, China