1. Department of Physics National University of Singapore 117542 Singapore Singapore
2. Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology School of Materials Science and Engineering Nanjing Institute of Technology 211100 Nanjing China
3. Department of Biomolecular Engineering Graduate School of Engineering Nagoya University 464-8603 Nagoya Japan
4. Integrated Science and Engineering Programme NUS Graduate School 119077 Singapore Singapore