**Author details**

Yuancheng Fan1\*, Fuli Zhang1 , Quanhong Fu1 and Hongqiang Li2

\*Address all correspondence to: phyfan@nwpu.edu.cn

1 Department of Applied Physics, School of Science, Northwestern Polytechnical University, Xi'an, China

2 The Institute of Dongguan–Tongji University, Dongguan, Guangdong, China
