1. State Key Laboratory for Mechanical Behavior of Materials; School of Materials Science and Engineering; Xi'an Jiaotong University; Xi'an Shaanxi 710049 P. R. China
2. Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems; School of Materials Science and Engineering; Beijing Institute of Technology; 5 Zhongguancun South Street, Haidian District Beijing 100081 P. R. China