1. CAS Key Laboratory of Nanophotonic Materials and Devices CAS Key Laboratory of Standardization and Measurement for Nanotechnology CAS Center for Excellence in Nanoscience National Center for Nanoscience and Technology Beijing 100190 P. R. China
2. Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Department of Electronic and Electrical Engineering University of Bath Bath BA2 7AY UK
4. Department of Physics National University of Defense Technology Changsha 410073 P. R. China
5. GBA Research Innovation Institute for Nanotechnology Guangzhou 510700 P. R. China