1. College of Materials Science and Engineering; Chongqing University; Chongqing 400044 P.R. China
2. Division of Physics and Applied Physics; School of Physical and Mathematical Sciences; Nanyang Technological University; 637371 Singapore
3. The State Key Laboratory of Mechanical Transmissions, and College of Aerospace Engineering; Chongqing University; Chongqing 400044 P.R. China
4. Key Laboratory of Low-grade Energy Utilization Technologies and Systems of the Ministry of Education of China; Chongqing 400044 China
5. College of Materials Science and Engineering; Hunan University; Changsha 410082 China