1. Materials Characterization and Preparation Center; Southern University of Science and Technology; Shenzhen 518055 China
2. School of Power and Mechanical Engineering; Wuhan University; Wuhan 430072 China
3. Institute of Materials Research and Engineering; A*STAR (Agency for Science, Technology and Research); 2 Fusionopolis Way, Innovis, #08-03 Singapore 138634
4. Department of Physics; National University of Singapore; 2 Science Drive 3 Singapore 117551