1. Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems; School of Materials Science and Engineering; Beijing Institute of Technology; Beijing 100081 P. R. China
2. Institute of Microstructure and Properties of Advanced Materials; Beijing University of Technology; Beijing 100124 P. R. China
3. School of Optical and Electronic Information; Huazhong University of Science and Technology; Wuhan 430074 P. R. China
4. Department of Materials Science and Engineering; College of Engineering; Peking University; Beijing 100871 P. R. China