1. School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054, P. R. China
2. Joint Laboratory of Police Equipment of UESTC, Chengdu, Sichuan 610054, P. R. China
3. Department
of Applied Physics, Hunan University, Changsha, Hunan 410082, P. R. China
4. Thin Film Centre, Scottish Universities Physics Alliance (SUPA), University of the West of Scotland, Paisley PA1 2BE, United Kingdom