1. School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
2. Nanofabrication facility, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, Jiangsu 215123, China
3. School of Physics, Southeast University, Nanjing 211189, China
4. Division of Nano-Devices and Technologies & Nanchang Key Laboratory of Advanced Packaging, Jiangxi Institute of Nanotechnology, SINANONC, Nanchang 330200, China
5. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China