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 310027 China
3. State Key Laboratory of Modern Optical Instrumentation; Zhejiang University; Hangzhou 310027 China
4. City University of Hong Kong Shenzhen Research Institute; Shenzhen 518057 China